[AliasSetTracker] Do not treat experimental_guard intrinsic as memory writing instruction
The `experimental_guard` intrinsic has memory write semantics to model the thread-exiting
logic, but does not do any actual writes to memory. Currently, `AliasSetTracker` treats it as a
normal memory write. As result, a loop-invariant load cannot be hoisted out of loop because
the guard may possibly alias with it.
This patch makes `AliasSetTracker` so that it doesn't treat guards as memory writes.
Differential Revision: https://reviews.llvm.org/D50497
Reviewed By: reames
llvm-svn: 339753
diff --git a/llvm/lib/Analysis/AliasSetTracker.cpp b/llvm/lib/Analysis/AliasSetTracker.cpp
index 65b61e4..1a495ec 100644
--- a/llvm/lib/Analysis/AliasSetTracker.cpp
+++ b/llvm/lib/Analysis/AliasSetTracker.cpp
@@ -24,6 +24,7 @@
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
+#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Support/AtomicOrdering.h"
@@ -169,7 +170,12 @@
addRef();
UnknownInsts.emplace_back(I);
- if (!I->mayWriteToMemory()) {
+ // Guards are marked as modifying memory for control flow modelling purposes,
+ // but don't actually modify any specific memory location.
+ using namespace PatternMatch;
+ bool MayWriteMemory = I->mayWriteToMemory() &&
+ !match(I, m_Intrinsic<Intrinsic::experimental_guard>());
+ if (!MayWriteMemory) {
Alias = SetMayAlias;
Access |= RefAccess;
return;