From a5a8546ac6ada30b59d3237d77fa74dc496f344c Mon Sep 17 00:00:00 2001
From: Philip Reames <listmail@philipreames.com>
Date: Tue, 21 Aug 2018 00:55:35 +0000
Subject: [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
---
 llvm/lib/Analysis/AliasSetTracker.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

(limited to 'llvm/lib/Analysis/AliasSetTracker.cpp')

diff --git a/llvm/lib/Analysis/AliasSetTracker.cpp b/llvm/lib/Analysis/AliasSetTracker.cpp
index 23c598d4edb..0470247cf6c 100644
--- a/llvm/lib/Analysis/AliasSetTracker.cpp
+++ b/llvm/lib/Analysis/AliasSetTracker.cpp
@@ -174,7 +174,8 @@ void AliasSet::addUnknownInst(Instruction *I, AliasAnalysis &AA) {
   // 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;
-- 
cgit v1.2.3