[AST] Mark invariant.starts as being readonly
These intrinsics are modelled as writing for control flow purposes, but they don't actually write to any location. Marking these - as we did for guards - allows LICM to hoist loads out of loops containing invariant.starts.
Differential Revision: https://reviews.llvm.org/D50861
llvm-svn: 340245
diff --git a/llvm/lib/Analysis/AliasSetTracker.cpp b/llvm/lib/Analysis/AliasSetTracker.cpp
index 23c598d..0470247 100644
--- a/llvm/lib/Analysis/AliasSetTracker.cpp
+++ b/llvm/lib/Analysis/AliasSetTracker.cpp
@@ -174,7 +174,8 @@
// but don't actually modify any specific memory location.
using namespace PatternMatch;
bool MayWriteMemory = I->mayWriteToMemory() &&
- !match(I, m_Intrinsic<Intrinsic::experimental_guard>());
+ !match(I, m_Intrinsic<Intrinsic::experimental_guard>()) &&
+ !(I->use_empty() && match(I, m_Intrinsic<Intrinsic::invariant_start>()));
if (!MayWriteMemory) {
Alias = SetMayAlias;
Access |= RefAccess;