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llvm-project/llvm/lib/Transforms/Scalar
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Juergen Ributzka 38b67d0caf Add Constant Hoisting Pass 
This pass identifies expensive constants to hoist and coalesces them to
better prepare it for SelectionDAG-based code generation. This works around the
limitations of the basic-block-at-a-time approach.

First it scans all instructions for integer constants and calculates its
cost. If the constant can be folded into the instruction (the cost is
TCC_Free) or the cost is just a simple operation (TCC_BASIC), then we don't
consider it expensive and leave it alone. This is the default behavior and
the default implementation of getIntImmCost will always return TCC_Free.

If the cost is more than TCC_BASIC, then the integer constant can't be folded
into the instruction and it might be beneficial to hoist the constant.
Similar constants are coalesced to reduce register pressure and
materialization code.

When a constant is hoisted, it is also hidden behind a bitcast to force it to
be live-out of the basic block. Otherwise the constant would be just
duplicated and each basic block would have its own copy in the SelectionDAG.
The SelectionDAG recognizes such constants as opaque and doesn't perform
certain transformations on them, which would create a new expensive constant.

This optimization is only applied to integer constants in instructions and
simple (this means not nested) constant cast experessions. For example:
%0 = load i64* inttoptr (i64 big_constant to i64*)

Reviewed by Eric

llvm-svn: 200022
 		2014-01-24 18:23:08 +00:00
..
ADCE.cpp Use SmallVectorImpl::iterator/const_iterator instead of SmallVector to avoid specifying the vector size. 2013-07-04 01:31:24 +00:00
CMakeLists.txt Add Constant Hoisting Pass 2014-01-24 18:23:08 +00:00
CodeGenPrepare.cpp Add Constant Hoisting Pass 2014-01-24 18:23:08 +00:00
ConstantHoisting.cpp Add Constant Hoisting Pass 2014-01-24 18:23:08 +00:00
ConstantProp.cpp Move all of the header files which are involved in modelling the LLVM IR 2013-01-02 11:36:10 +00:00
CorrelatedValuePropagation.cpp CVP: If we have a PHI with an incoming select, try to skip the select. 2013-02-24 15:34:43 +00:00
DCE.cpp Move all of the header files which are involved in modelling the LLVM IR 2013-01-02 11:36:10 +00:00
DeadStoreElimination.cpp [PM] Split DominatorTree into a concrete analysis result object which 2014-01-13 13:07:17 +00:00
EarlyCSE.cpp [PM] Split DominatorTree into a concrete analysis result object which 2014-01-13 13:07:17 +00:00
FlattenCFGPass.cpp Factor FlattenCFG out from SimplifyCFG 2013-08-06 02:43:45 +00:00
GVN.cpp [PM] Split DominatorTree into a concrete analysis result object which 2014-01-13 13:07:17 +00:00
GlobalMerge.cpp Change tabs to spaces. 2013-07-22 21:11:30 +00:00
IndVarSimplify.cpp [PM] Split DominatorTree into a concrete analysis result object which 2014-01-13 13:07:17 +00:00
JumpThreading.cpp Don't eliminate a partially redundant load if it's in a landing pad. 2013-10-21 04:09:17 +00:00
LICM.cpp [LPM] Fix a logic error in LICM spotted by inspection. 2014-01-24 02:24:47 +00:00
LLVMBuild.txt Add proper dependencies to LLVMBuild.txt in llvm/lib. 2013-12-10 05:39:34 +00:00
LoopDeletion.cpp [PM] Split DominatorTree into a concrete analysis result object which 2014-01-13 13:07:17 +00:00
LoopIdiomRecognize.cpp Fix known typos 2014-01-24 17:20:08 +00:00
LoopInstSimplify.cpp [PM] Split DominatorTree into a concrete analysis result object which 2014-01-13 13:07:17 +00:00
LoopRerollPass.cpp [PM] Split DominatorTree into a concrete analysis result object which 2014-01-13 13:07:17 +00:00
LoopRotation.cpp [PM] Split DominatorTree into a concrete analysis result object which 2014-01-13 13:07:17 +00:00
LoopStrengthReduce.cpp Loop strength reduce: fix function name. 2014-01-22 13:27:00 +00:00
LoopUnrollPass.cpp [LPM] Make LoopSimplify no longer a LoopPass and instead both a utility 2014-01-23 11:23:19 +00:00
LoopUnswitch.cpp [PM] Split DominatorTree into a concrete analysis result object which 2014-01-13 13:07:17 +00:00
LowerAtomic.cpp Move all of the header files which are involved in modelling the LLVM IR 2013-01-02 11:36:10 +00:00
Makefile
…
MemCpyOptimizer.cpp Handle an addrspacecast case in memcpyopt 2014-01-22 21:53:19 +00:00
PartiallyInlineLibCalls.cpp Turn MipsOptimizeMathLibCalls into a target-independent scalar transform 2013-08-23 10:27:02 +00:00
Reassociate.cpp Put the functionality for printing a value to a raw_ostream as an 2014-01-09 02:29:41 +00:00
Reg2Mem.cpp Move all of the header files which are involved in modelling the LLVM IR 2013-01-02 11:36:10 +00:00
SCCP.cpp Use SmallVectorImpl& instead of SmallVector to avoid repeating small vector size. 2013-07-14 04:42:23 +00:00
SROA.cpp [SROA] Fix a bug which could cause the common type finding to return 2014-01-21 23:16:05 +00:00
SampleProfile.cpp [PM] Split DominatorTree into a concrete analysis result object which 2014-01-13 13:07:17 +00:00
Scalar.cpp Add Constant Hoisting Pass 2014-01-24 18:23:08 +00:00
ScalarReplAggregates.cpp [PM] Split DominatorTree into a concrete analysis result object which 2014-01-13 13:07:17 +00:00
Scalarizer.cpp Fix Scalarizer insertion point when replacing PHIs with insertelements 2013-12-23 14:51:56 +00:00
SimplifyCFGPass.cpp Reapply r188119 now that the bug it exposed is fixed. 2013-08-12 22:38:43 +00:00
Sink.cpp [PM] Split DominatorTree into a concrete analysis result object which 2014-01-13 13:07:17 +00:00
StructurizeCFG.cpp [PM] Split DominatorTree into a concrete analysis result object which 2014-01-13 13:07:17 +00:00
TailRecursionElimination.cpp TRE: Move class into anonymous namespace. 2013-07-24 16:12:08 +00:00