[PATCH] D66604: [GVN] AnalyzeLoadAvailability: Replace a load after lifetime.end with undef (PR20811)

[Shreyansh Chouhan via Phabricator via llvm-commits]

BK1603 updated this revision to Diff 218267.
BK1603 added a comment.

Replaced conditionals at original position.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D66604/new/

https://reviews.llvm.org/D66604

Files:
  llvm/lib/Transforms/Scalar/GVN.cpp
  llvm/test/Transforms/GVN/lifetime-end.ll


Index: llvm/test/Transforms/GVN/lifetime-end.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/GVN/lifetime-end.ll
@@ -0,0 +1,13 @@
+; RUN: opt < %s -basicaa -gvn -S | FileCheck %s
+
+define i8 @test(i8* %P) nounwind {
+; CHECK: lifetime.end
+; CHECK-NOT: load
+; CHECK:  ret i8 undef
+entry:
+  call void @llvm.lifetime.end(i64 32, i8* %P)
+  %0 = load i8, i8* %P
+  ret i8 %0
+}
+
+declare void @llvm.lifetime.end(i64 %S, i8* nocapture %P)
Index: llvm/lib/Transforms/Scalar/GVN.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/GVN.cpp
+++ llvm/lib/Transforms/Scalar/GVN.cpp
@@ -822,6 +822,12 @@
   return false;
 }
 
+static bool isLifetimeEnd(const Instruction *Inst) {
+  if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst))
+    return II->getIntrinsicID() == Intrinsic::lifetime_end;
+  return false;
+}
+
 /// Try to locate the three instruction involved in a missed
 /// load-elimination case that is due to an intervening store.
 static void reportMayClobberedLoad(LoadInst *LI, MemDepResult DepInfo,
@@ -864,7 +870,15 @@
   const DataLayout &DL = LI->getModule()->getDataLayout();
 
   Instruction *DepInst = DepInfo.getInst();
+
   if (DepInfo.isClobber()) {
+
+		// Load immediately after lifetime end -> undef
+		if(isLifetimeEnd(DepInst)) {
+			Res = AvailableValue::get(UndefValue::get(LI->getType()));
+			return true;
+		}
+
     // If the dependence is to a store that writes to a superset of the bits
     // read by the load, we can extract the bits we need for the load from the
     // stored value.


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