[LICM] Make isGuaranteedToExecute more accurate.
Summary:
Make isGuaranteedToExecute use the
isGuaranteedToTransferExecutionToSuccessor helper, and make that helper
a bit more accurate.
There's a potential performance impact here from assuming that arbitrary
calls might not return. This probably has little impact on loads and
stores to a pointer because most things alias analysis can reason about
are dereferenceable anyway. The other impacts, like less aggressive
hoisting of sdiv by a variable and less aggressive hoisting around
volatile memory operations, are unlikely to matter for real code.
This also impacts SCEV, which uses the same helper. It's a minor
improvement there because we can tell that, for example, memcpy always
returns normally. Strictly speaking, it's also introducing
a bug, but it's not any worse than everywhere else we assume readonly
functions terminate.
Fixes http://llvm.org/PR27857.
Reviewers: hfinkel, reames, chandlerc, sanjoy
Subscribers: broune, llvm-commits
Differential Revision: http://reviews.llvm.org/D21167
llvm-svn: 272489
diff --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index 8f7cace..b67bd24 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -388,7 +388,7 @@
// Iterate over header and compute safety info.
for (BasicBlock::iterator I = Header->begin(), E = Header->end();
(I != E) && !SafetyInfo->HeaderMayThrow; ++I)
- SafetyInfo->HeaderMayThrow |= I->mayThrow();
+ SafetyInfo->HeaderMayThrow |= !isGuaranteedToTransferExecutionToSuccessor(&*I);
SafetyInfo->MayThrow = SafetyInfo->HeaderMayThrow;
// Iterate over loop instructions and compute safety info.
@@ -397,7 +397,7 @@
(BB != BBE) && !SafetyInfo->MayThrow; ++BB)
for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end();
(I != E) && !SafetyInfo->MayThrow; ++I)
- SafetyInfo->MayThrow |= I->mayThrow();
+ SafetyInfo->MayThrow |= !isGuaranteedToTransferExecutionToSuccessor(&*I);
// Compute funclet colors if we might sink/hoist in a function with a funclet
// personality routine.