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Now that we look at all the header PHIs, we need to consider all the header PHIs 

when deciding that the loop has stopped evolving. Fixes miscompile in the gcc
torture testsuite!

llvm-svn: 142843
This commit is contained in:
Nick Lewycky 2011-10-24 21:02:38 +00:00
parent b72d55353a
commit a58fb48a55
2 changed files with 43 additions and 6 deletions
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16
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -4844,12 +4844,12 @@ ScalarEvolution::getConstantEvolutionLoopExitValue(PHINode *PN,
// EvaluateExpression adds non-phi values to the CurrentIterVals map. // EvaluateExpression adds non-phi values to the CurrentIterVals map.
DenseMap<Instruction *, Constant *> NextIterVals; DenseMap<Instruction *, Constant *> NextIterVals;
Constant *NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, TD); Constant *NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, TD);
if (NextPHI == CurrentIterVals[PN])
return RetVal = NextPHI; // Stopped evolving!
if (NextPHI == 0) if (NextPHI == 0)
return 0; // Couldn't evaluate! return 0; // Couldn't evaluate!
NextIterVals[PN] = NextPHI; NextIterVals[PN] = NextPHI;
bool StoppedEvolving = NextPHI == CurrentIterVals[PN];
// Also evaluate the other PHI nodes. However, we don't get to stop if we // Also evaluate the other PHI nodes. However, we don't get to stop if we
// cease to be able to evaluate one of them or if they stop evolving, // cease to be able to evaluate one of them or if they stop evolving,
// because that doesn't necessarily prevent us from computing PN. // because that doesn't necessarily prevent us from computing PN.
@ -4858,11 +4858,19 @@ ScalarEvolution::getConstantEvolutionLoopExitValue(PHINode *PN,
PHINode *PHI = dyn_cast<PHINode>(I->first); PHINode *PHI = dyn_cast<PHINode>(I->first);
if (!PHI || PHI == PN || PHI->getParent() != Header) continue; if (!PHI || PHI == PN || PHI->getParent() != Header) continue;
Constant *&NextPHI = NextIterVals[PHI]; Constant *&NextPHI = NextIterVals[PHI];
if (NextPHI) continue; // Already computed! if (!NextPHI) { // Not already computed.
Value *BEValue = PHI->getIncomingValue(SecondIsBackedge); Value *BEValue = PHI->getIncomingValue(SecondIsBackedge);
NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, TD); NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, TD);
} }
if (NextPHI != I->second)
StoppedEvolving = false;
}
// If all entries in CurrentIterVals == NextIterVals then we can stop
// iterating, the loop can't continue to change.
if (StoppedEvolving)
return RetVal = CurrentIterVals[PN];
CurrentIterVals.swap(NextIterVals); CurrentIterVals.swap(NextIterVals);
} }
} }

29
llvm/test/Analysis/ScalarEvolution/trip-count11.ll Normal file
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@ -0,0 +1,29 @@
; RUN: opt < %s -analyze -scalar-evolution | FileCheck %s
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
@foo.a = internal constant [8 x i32] [i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7], align 16
define i32 @foo() nounwind uwtable noinline {
entry:
br label %for.cond
for.cond: ; preds = %for.inc, %entry
%sum.0 = phi i32 [ 0, %entry ], [ %add, %for.inc ]
; CHECK: --> %sum.0 Exits: 28
%i.0 = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
%cmp = icmp ult i32 %i.0, 8
br i1 %cmp, label %for.inc, label %for.end
for.inc: ; preds = %for.cond
%idxprom = sext i32 %i.0 to i64
%arrayidx = getelementptr inbounds [8 x i32]* @foo.a, i64 0, i64 %idxprom
%0 = load i32* %arrayidx, align 4
%add = add nsw i32 %sum.0, %0
%inc = add nsw i32 %i.0, 1
br label %for.cond
for.end: ; preds = %for.cond
ret i32 %sum.0
}