From 99890a225f80495468174becb876a560f4383cea Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Tue, 2 Aug 2011 21:19:27 +0000
Subject: Lifetime intrinsics on undef are dead.

llvm-svn: 136722
---
 llvm/lib/Transforms/Utils/Local.cpp | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

(limited to 'llvm/lib/Transforms/Utils/Local.cpp')

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 2d43e3773ef..60dc15d6425 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -229,10 +229,10 @@ bool llvm::isInstructionTriviallyDead(Instruction *I) {
   // We don't want debug info removed by anything this general, unless
   // debug info is empty.
   if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
-    if (DDI->getAddress()) 
+    if (DDI->getAddress())
       return false;
     return true;
-  } 
+  }
   if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
     if (DVI->getValue())
       return false;
@@ -243,10 +243,16 @@ bool llvm::isInstructionTriviallyDead(Instruction *I) {
 
   // Special case intrinsics that "may have side effects" but can be deleted
   // when dead.
-  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
+  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
     // Safe to delete llvm.stacksave if dead.
     if (II->getIntrinsicID() == Intrinsic::stacksave)
       return true;
+
+    // Lifetime intrinsics are dead when their right-hand is undef.
+    if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
+        II->getIntrinsicID() == Intrinsic::lifetime_end)
+      return isa<UndefValue>(II->getArgOperand(1));
+  }
   return false;
 }
 
-- 
cgit v1.2.3