fix PR9841 by having GVN not process dead loads. This was

causing it to get into infinite loops when it would widen a 
load (which can necessarily leave around dead loads).

llvm-svn: 131847

2 files changed, 17 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp
index 1da5238bbb6..2515fd112c1 100644
--- a/llvm/lib/Transforms/Scalar/GVN.cpp
+++ b/llvm/lib/Transforms/Scalar/GVN.cpp
@@ -1607,6 +1607,11 @@ bool GVN::processLoad(LoadInst *L) {
   if (L->isVolatile())
     return false;
 
+  if (L->use_empty()) {
+    markInstructionForDeletion(L);
+    return true;
+  }
+  
   // ... to a pointer that has been loaded from before...
   MemDepResult Dep = MD->getDependency(L);
 
diff --git a/llvm/test/Transforms/GVN/crash.ll b/llvm/test/Transforms/GVN/crash.ll
index 4a3aa1c55a8..31eae256c6e 100644
--- a/llvm/test/Transforms/GVN/crash.ll
+++ b/llvm/test/Transforms/GVN/crash.ll
@@ -151,3 +151,15 @@ dead:
 dead2:
   ret i32 %A
 }
+
+
+; PR9841
+define fastcc i8 @test5(i8* %P) nounwind {
+entry:
+  %0 = load i8* %P, align 2
+
+  %Q = getelementptr i8* %P, i32 1
+  %1 = load i8* %Q, align 1
+  ret i8 %1
+}
+