diff options
| author | Dan Gohman <gohman@apple.com> | 2008-07-24 23:57:25 +0000 |
|---|---|---|
| committer | Dan Gohman <gohman@apple.com> | 2008-07-24 23:57:25 +0000 |
| commit | 3eee6542f5c65dce299361fa5435340513cf3fe4 (patch) | |
| tree | 55d9ae6062c7004acf53c75fee45371cb313db70 | |
| parent | 5444c307239b349af7a2bd7af2406a6c1709b7f1 (diff) | |
Put the LICM of constant GlobalVariables, introduced in r53945, under a
command-line option, and disable it by default. It introduced performance
regressions because CodeGen is currently not able to remat such loads.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53997 91177308-0d34-0410-b5e6-96231b3b80d8
| -rw-r--r-- | lib/Transforms/Scalar/LICM.cpp | 12 | ||||
| -rw-r--r-- | test/Transforms/LICM/2008-07-22-LoadGlobalConstant.ll | 2 |
2 files changed, 12 insertions, 2 deletions
diff --git a/lib/Transforms/Scalar/LICM.cpp b/lib/Transforms/Scalar/LICM.cpp index 13440c13b6..aef1cd6f6f 100644 --- a/lib/Transforms/Scalar/LICM.cpp +++ b/lib/Transforms/Scalar/LICM.cpp @@ -62,6 +62,15 @@ 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 VISIBILITY_HIDDEN LICM : public LoopPass { static char ID; // Pass identification, replacement for typeid @@ -372,7 +381,8 @@ 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 (AA->pointsToConstantMemory(LI->getOperand(0))) + if (EnableLICMConstantMotion && + AA->pointsToConstantMemory(LI->getOperand(0))) return true; // Don't hoist loads which have may-aliased stores in loop. diff --git a/test/Transforms/LICM/2008-07-22-LoadGlobalConstant.ll b/test/Transforms/LICM/2008-07-22-LoadGlobalConstant.ll index c3af29bf43..3824d53597 100644 --- a/test/Transforms/LICM/2008-07-22-LoadGlobalConstant.ll +++ b/test/Transforms/LICM/2008-07-22-LoadGlobalConstant.ll @@ -1,4 +1,4 @@ -; RUN: llvm-as < %s | opt -licm | llvm-dis | grep -A 1 entry | grep load.*@a +; RUN: llvm-as < %s | opt -licm -enable-licm-constant-variables | llvm-dis | grep -A 1 entry | grep load.*@a @a = external constant float* define void @test(i32 %count) { |