482 lines
17 KiB
C++
482 lines
17 KiB
C++
//===-- ConstantFolding.cpp - Analyze constant folding possibilities ------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This family of functions determines the possibility of performing constant
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// folding.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/ConstantFolding.h"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/Intrinsics.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Support/GetElementPtrTypeIterator.h"
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#include "llvm/Support/MathExtras.h"
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#include <cerrno>
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#include <cmath>
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using namespace llvm;
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//===----------------------------------------------------------------------===//
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// Constant Folding internal helper functions
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//===----------------------------------------------------------------------===//
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/// IsConstantOffsetFromGlobal - If this constant is actually a constant offset
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/// from a global, return the global and the constant. Because of
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/// constantexprs, this function is recursive.
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static bool IsConstantOffsetFromGlobal(Constant *C, GlobalValue *&GV,
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int64_t &Offset, const TargetData &TD) {
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// Trivial case, constant is the global.
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if ((GV = dyn_cast<GlobalValue>(C))) {
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Offset = 0;
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return true;
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}
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// Otherwise, if this isn't a constant expr, bail out.
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ConstantExpr *CE = dyn_cast<ConstantExpr>(C);
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if (!CE) return false;
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// Look through ptr->int and ptr->ptr casts.
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if (CE->getOpcode() == Instruction::PtrToInt ||
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CE->getOpcode() == Instruction::BitCast)
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return IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD);
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// i32* getelementptr ([5 x i32]* @a, i32 0, i32 5)
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if (CE->getOpcode() == Instruction::GetElementPtr) {
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// Cannot compute this if the element type of the pointer is missing size
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// info.
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if (!cast<PointerType>(CE->getOperand(0)->getType())->getElementType()->isSized())
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return false;
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// If the base isn't a global+constant, we aren't either.
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if (!IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD))
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return false;
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// Otherwise, add any offset that our operands provide.
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gep_type_iterator GTI = gep_type_begin(CE);
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for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i, ++GTI) {
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ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(i));
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if (!CI) return false; // Index isn't a simple constant?
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if (CI->getZExtValue() == 0) continue; // Not adding anything.
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if (const StructType *ST = dyn_cast<StructType>(*GTI)) {
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// N = N + Offset
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Offset += TD.getStructLayout(ST)->getElementOffset(CI->getZExtValue());
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} else {
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const SequentialType *SQT = cast<SequentialType>(*GTI);
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Offset += TD.getTypeSize(SQT->getElementType())*CI->getSExtValue();
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}
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}
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return true;
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}
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return false;
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}
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/// SymbolicallyEvaluateBinop - One of Op0/Op1 is a constant expression.
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/// Attempt to symbolically evaluate the result of a binary operator merging
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/// these together. If target data info is available, it is provided as TD,
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/// otherwise TD is null.
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static Constant *SymbolicallyEvaluateBinop(unsigned Opc, Constant *Op0,
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Constant *Op1, const TargetData *TD){
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// SROA
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// Fold (and 0xffffffff00000000, (shl x, 32)) -> shl.
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// Fold (lshr (or X, Y), 32) -> (lshr [X/Y], 32) if one doesn't contribute
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// bits.
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// If the constant expr is something like &A[123] - &A[4].f, fold this into a
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// constant. This happens frequently when iterating over a global array.
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if (Opc == Instruction::Sub && TD) {
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GlobalValue *GV1, *GV2;
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int64_t Offs1, Offs2;
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if (IsConstantOffsetFromGlobal(Op0, GV1, Offs1, *TD))
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if (IsConstantOffsetFromGlobal(Op1, GV2, Offs2, *TD) &&
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GV1 == GV2) {
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// (&GV+C1) - (&GV+C2) -> C1-C2, pointer arithmetic cannot overflow.
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return ConstantInt::get(Op0->getType(), Offs1-Offs2);
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}
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}
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// TODO: Fold icmp setne/seteq as well.
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return 0;
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}
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/// SymbolicallyEvaluateGEP - If we can symbolically evaluate the specified GEP
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/// constant expression, do so.
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static Constant *SymbolicallyEvaluateGEP(Constant** Ops, unsigned NumOps,
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const Type *ResultTy,
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const TargetData *TD) {
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Constant *Ptr = Ops[0];
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if (!cast<PointerType>(Ptr->getType())->getElementType()->isSized())
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return 0;
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if (TD && Ptr->isNullValue()) {
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// If this is a constant expr gep that is effectively computing an
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// "offsetof", fold it into 'cast int Size to T*' instead of 'gep 0, 0, 12'
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bool isFoldableGEP = true;
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for (unsigned i = 1; i != NumOps; ++i)
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if (!isa<ConstantInt>(Ops[i])) {
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isFoldableGEP = false;
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break;
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}
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if (isFoldableGEP) {
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uint64_t Offset = TD->getIndexedOffset(Ptr->getType(),
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(Value**)Ops+1, NumOps-1);
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Constant *C = ConstantInt::get(TD->getIntPtrType(), Offset);
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return ConstantExpr::getIntToPtr(C, ResultTy);
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}
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}
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return 0;
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}
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//===----------------------------------------------------------------------===//
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// Constant Folding public APIs
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//===----------------------------------------------------------------------===//
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/// ConstantFoldInstruction - Attempt to constant fold the specified
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/// instruction. If successful, the constant result is returned, if not, null
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/// is returned. Note that this function can only fail when attempting to fold
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/// instructions like loads and stores, which have no constant expression form.
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///
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Constant *llvm::ConstantFoldInstruction(Instruction *I, const TargetData *TD) {
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if (PHINode *PN = dyn_cast<PHINode>(I)) {
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if (PN->getNumIncomingValues() == 0)
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return Constant::getNullValue(PN->getType());
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Constant *Result = dyn_cast<Constant>(PN->getIncomingValue(0));
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if (Result == 0) return 0;
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// Handle PHI nodes specially here...
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for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
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if (PN->getIncomingValue(i) != Result && PN->getIncomingValue(i) != PN)
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return 0; // Not all the same incoming constants...
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// If we reach here, all incoming values are the same constant.
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return Result;
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}
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// Scan the operand list, checking to see if they are all constants, if so,
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// hand off to ConstantFoldInstOperands.
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SmallVector<Constant*, 8> Ops;
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for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
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if (Constant *Op = dyn_cast<Constant>(I->getOperand(i)))
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Ops.push_back(Op);
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else
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return 0; // All operands not constant!
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return ConstantFoldInstOperands(I, &Ops[0], Ops.size(), TD);
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}
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/// ConstantFoldInstOperands - Attempt to constant fold an instruction with the
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/// specified opcode and operands. If successful, the constant result is
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/// returned, if not, null is returned. Note that this function can fail when
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/// attempting to fold instructions like loads and stores, which have no
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/// constant expression form.
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///
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Constant *llvm::ConstantFoldInstOperands(const Instruction* I,
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Constant** Ops, unsigned NumOps,
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const TargetData *TD) {
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unsigned Opc = I->getOpcode();
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const Type *DestTy = I->getType();
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// Handle easy binops first.
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if (isa<BinaryOperator>(I)) {
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if (isa<ConstantExpr>(Ops[0]) || isa<ConstantExpr>(Ops[1]))
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if (Constant *C = SymbolicallyEvaluateBinop(I->getOpcode(), Ops[0],
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Ops[1], TD))
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return C;
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return ConstantExpr::get(Opc, Ops[0], Ops[1]);
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}
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switch (Opc) {
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default: return 0;
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case Instruction::Call:
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if (Function *F = dyn_cast<Function>(Ops[0]))
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if (canConstantFoldCallTo(F))
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return ConstantFoldCall(F, Ops+1, NumOps-1);
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return 0;
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case Instruction::ICmp:
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case Instruction::FCmp:
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return ConstantExpr::getCompare(cast<CmpInst>(I)->getPredicate(), Ops[0],
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Ops[1]);
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case Instruction::Trunc:
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case Instruction::ZExt:
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case Instruction::SExt:
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case Instruction::FPTrunc:
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case Instruction::FPExt:
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case Instruction::UIToFP:
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case Instruction::SIToFP:
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case Instruction::FPToUI:
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case Instruction::FPToSI:
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case Instruction::PtrToInt:
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case Instruction::IntToPtr:
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case Instruction::BitCast:
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return ConstantExpr::getCast(Opc, Ops[0], DestTy);
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case Instruction::Select:
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return ConstantExpr::getSelect(Ops[0], Ops[1], Ops[2]);
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case Instruction::ExtractElement:
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return ConstantExpr::getExtractElement(Ops[0], Ops[1]);
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case Instruction::InsertElement:
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return ConstantExpr::getInsertElement(Ops[0], Ops[1], Ops[2]);
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case Instruction::ShuffleVector:
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return ConstantExpr::getShuffleVector(Ops[0], Ops[1], Ops[2]);
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case Instruction::GetElementPtr:
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if (Constant *C = SymbolicallyEvaluateGEP(Ops, NumOps, I->getType(), TD))
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return C;
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return ConstantExpr::getGetElementPtr(Ops[0], Ops+1, NumOps-1);
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}
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}
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/// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a
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/// getelementptr constantexpr, return the constant value being addressed by the
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/// constant expression, or null if something is funny and we can't decide.
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Constant *llvm::ConstantFoldLoadThroughGEPConstantExpr(Constant *C,
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ConstantExpr *CE) {
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if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType()))
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return 0; // Do not allow stepping over the value!
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// Loop over all of the operands, tracking down which value we are
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// addressing...
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gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
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for (++I; I != E; ++I)
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if (const StructType *STy = dyn_cast<StructType>(*I)) {
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ConstantInt *CU = cast<ConstantInt>(I.getOperand());
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assert(CU->getZExtValue() < STy->getNumElements() &&
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"Struct index out of range!");
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unsigned El = (unsigned)CU->getZExtValue();
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if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
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C = CS->getOperand(El);
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} else if (isa<ConstantAggregateZero>(C)) {
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C = Constant::getNullValue(STy->getElementType(El));
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} else if (isa<UndefValue>(C)) {
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C = UndefValue::get(STy->getElementType(El));
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} else {
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return 0;
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}
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} else if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) {
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if (const ArrayType *ATy = dyn_cast<ArrayType>(*I)) {
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if (CI->getZExtValue() >= ATy->getNumElements())
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return 0;
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if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
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C = CA->getOperand(CI->getZExtValue());
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else if (isa<ConstantAggregateZero>(C))
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C = Constant::getNullValue(ATy->getElementType());
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else if (isa<UndefValue>(C))
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C = UndefValue::get(ATy->getElementType());
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else
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return 0;
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} else if (const VectorType *PTy = dyn_cast<VectorType>(*I)) {
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if (CI->getZExtValue() >= PTy->getNumElements())
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return 0;
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if (ConstantVector *CP = dyn_cast<ConstantVector>(C))
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C = CP->getOperand(CI->getZExtValue());
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else if (isa<ConstantAggregateZero>(C))
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C = Constant::getNullValue(PTy->getElementType());
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else if (isa<UndefValue>(C))
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C = UndefValue::get(PTy->getElementType());
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else
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return 0;
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} else {
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return 0;
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}
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} else {
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return 0;
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}
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return C;
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}
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//===----------------------------------------------------------------------===//
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// Constant Folding for Calls
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//
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/// canConstantFoldCallTo - Return true if its even possible to fold a call to
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/// the specified function.
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bool
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llvm::canConstantFoldCallTo(Function *F) {
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const std::string &Name = F->getName();
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switch (F->getIntrinsicID()) {
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case Intrinsic::sqrt_f32:
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case Intrinsic::sqrt_f64:
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case Intrinsic::powi_f32:
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case Intrinsic::powi_f64:
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case Intrinsic::bswap:
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case Intrinsic::ctpop:
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case Intrinsic::ctlz:
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case Intrinsic::cttz:
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return true;
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default: break;
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}
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switch (Name[0])
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{
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case 'a':
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return Name == "acos" || Name == "asin" || Name == "atan" ||
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Name == "atan2";
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case 'c':
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return Name == "ceil" || Name == "cos" || Name == "cosf" ||
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Name == "cosh";
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case 'e':
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return Name == "exp";
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case 'f':
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return Name == "fabs" || Name == "fmod" || Name == "floor";
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case 'l':
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return Name == "log" || Name == "log10";
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case 'p':
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return Name == "pow";
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case 's':
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return Name == "sin" || Name == "sinh" ||
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Name == "sqrt" || Name == "sqrtf";
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case 't':
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return Name == "tan" || Name == "tanh";
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default:
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return false;
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}
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}
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static Constant *ConstantFoldFP(double (*NativeFP)(double), double V,
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const Type *Ty) {
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errno = 0;
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V = NativeFP(V);
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if (errno == 0)
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return ConstantFP::get(Ty, V);
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errno = 0;
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return 0;
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}
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/// ConstantFoldCall - Attempt to constant fold a call to the specified function
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/// with the specified arguments, returning null if unsuccessful.
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Constant *
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llvm::ConstantFoldCall(Function *F, Constant** Operands, unsigned NumOperands) {
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const std::string &Name = F->getName();
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const Type *Ty = F->getReturnType();
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if (NumOperands == 1) {
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if (ConstantFP *Op = dyn_cast<ConstantFP>(Operands[0])) {
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double V = Op->getValue();
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switch (Name[0])
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{
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case 'a':
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if (Name == "acos")
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return ConstantFoldFP(acos, V, Ty);
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else if (Name == "asin")
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return ConstantFoldFP(asin, V, Ty);
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else if (Name == "atan")
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return ConstantFP::get(Ty, atan(V));
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break;
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case 'c':
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if (Name == "ceil")
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return ConstantFoldFP(ceil, V, Ty);
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else if (Name == "cos")
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return ConstantFP::get(Ty, cos(V));
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else if (Name == "cosh")
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return ConstantFP::get(Ty, cosh(V));
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break;
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case 'e':
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if (Name == "exp")
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return ConstantFP::get(Ty, exp(V));
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break;
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case 'f':
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if (Name == "fabs")
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return ConstantFP::get(Ty, fabs(V));
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else if (Name == "floor")
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return ConstantFoldFP(floor, V, Ty);
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break;
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case 'l':
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if (Name == "log" && V > 0)
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return ConstantFP::get(Ty, log(V));
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else if (Name == "log10" && V > 0)
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return ConstantFoldFP(log10, V, Ty);
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else if (Name == "llvm.sqrt.f32" || Name == "llvm.sqrt.f64") {
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if (V >= -0.0)
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return ConstantFP::get(Ty, sqrt(V));
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else // Undefined
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return ConstantFP::get(Ty, 0.0);
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}
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break;
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case 's':
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if (Name == "sin")
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return ConstantFP::get(Ty, sin(V));
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else if (Name == "sinh")
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return ConstantFP::get(Ty, sinh(V));
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else if (Name == "sqrt" && V >= 0)
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return ConstantFP::get(Ty, sqrt(V));
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else if (Name == "sqrtf" && V >= 0)
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return ConstantFP::get(Ty, sqrt((float)V));
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break;
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case 't':
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if (Name == "tan")
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return ConstantFP::get(Ty, tan(V));
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else if (Name == "tanh")
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return ConstantFP::get(Ty, tanh(V));
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break;
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default:
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break;
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}
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} else if (ConstantInt *Op = dyn_cast<ConstantInt>(Operands[0])) {
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if (Name.size() > 11 && !memcmp(&Name[0], "llvm.bswap", 10)) {
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return ConstantInt::get(Op->getValue().byteSwap());
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} else if (Name.size() > 11 && !memcmp(&Name[0],"llvm.ctpop",10)) {
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uint64_t ctpop = Op->getValue().countPopulation();
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return ConstantInt::get(Type::Int32Ty, ctpop);
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} else if (Name.size() > 10 && !memcmp(&Name[0], "llvm.cttz", 9)) {
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uint64_t cttz = Op->getValue().countTrailingZeros();
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return ConstantInt::get(Type::Int32Ty, cttz);
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} else if (Name.size() > 10 && !memcmp(&Name[0], "llvm.ctlz", 9)) {
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uint64_t ctlz = Op->getValue().countLeadingZeros();
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return ConstantInt::get(Type::Int32Ty, ctlz);
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}
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}
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} else if (NumOperands == 2) {
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if (ConstantFP *Op1 = dyn_cast<ConstantFP>(Operands[0])) {
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double Op1V = Op1->getValue();
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if (ConstantFP *Op2 = dyn_cast<ConstantFP>(Operands[1])) {
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double Op2V = Op2->getValue();
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if (Name == "pow") {
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errno = 0;
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double V = pow(Op1V, Op2V);
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if (errno == 0)
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return ConstantFP::get(Ty, V);
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} else if (Name == "fmod") {
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errno = 0;
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double V = fmod(Op1V, Op2V);
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if (errno == 0)
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return ConstantFP::get(Ty, V);
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} else if (Name == "atan2") {
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return ConstantFP::get(Ty, atan2(Op1V,Op2V));
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}
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} else if (ConstantInt *Op2C = dyn_cast<ConstantInt>(Operands[1])) {
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if (Name == "llvm.powi.f32") {
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return ConstantFP::get(Ty, std::pow((float)Op1V,
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(int)Op2C->getZExtValue()));
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} else if (Name == "llvm.powi.f64") {
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return ConstantFP::get(Ty, std::pow((double)Op1V,
|
|
(int)Op2C->getZExtValue()));
|
|
}
|
|
}
|
|
}
|
|
}
|
|
return 0;
|
|
}
|
|
|