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Enable hoisting of loads from constant memory by default. In cases where

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they are lowered to instruction sequences more complex than a simple
load, such that CodeGen cannot rematerialize them, a reload from a
spill slot is likely to be cheaper than the complex sequence.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89374 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-11-19 19:00:10 +00:00
parent 58ce7acb4f
commit dab249b3b7
2 changed files with 2 additions and 12 deletions
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12
lib/Transforms/Scalar/LICM.cpp
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@ -63,15 +63,6 @@ static cl::opt<bool>
DisablePromotion("disable-licm-promotion", cl::Hidden,
cl::desc("Disable memory promotion in LICM pass"));
// This feature is currently disabled by default because CodeGen is not yet
// capable of rematerializing these constants in PIC mode, so it can lead to
// degraded performance. Compile test/CodeGen/X86/remat-constant.ll with
// -relocation-model=pic to see an example of this.
static cl::opt<bool>
EnableLICMConstantMotion("enable-licm-constant-variables", cl::Hidden,
cl::desc("Enable hoisting/sinking of constant "
"global variables"));
namespace {
struct LICM : public LoopPass {
static char ID; // Pass identification, replacement for typeid
@ -383,8 +374,7 @@ bool LICM::canSinkOrHoistInst(Instruction &I) {
// Loads from constant memory are always safe to move, even if they end up
// in the same alias set as something that ends up being modified.
if (EnableLICMConstantMotion &&
AA->pointsToConstantMemory(LI->getOperand(0)))
if (AA->pointsToConstantMemory(LI->getOperand(0)))
return true;
// Don't hoist loads which have may-aliased stores in loop.

2
test/Transforms/LICM/2008-07-22-LoadGlobalConstant.ll
View File

@ -1,4 +1,4 @@
; RUN: opt < %s -licm -enable-licm-constant-variables -S | FileCheck %s
; RUN: opt < %s -licm -S | FileCheck %s
@a = external constant float*