[llvm] r334187 - [Mem2Reg] Avoid replacing load with itself in promoteSingleBlockAlloca.

[Florian Hahn via llvm-commits]

Author: fhahn
Date: Thu Jun  7 04:09:05 2018
New Revision: 334187

URL: http://llvm.org/viewvc/llvm-project?rev=334187&view=rev
Log:
[Mem2Reg] Avoid replacing load with itself in promoteSingleBlockAlloca.

We do the same thing in rewriteSingleStoreAlloca.

Fixes PR37632.

Reviewers: chandlerc, davide, efriedma

Reviewed By: davide

Differential Revision: https://reviews.llvm.org/D47825

Added:
    llvm/trunk/test/Transforms/Mem2Reg/pr37632-unreachable-list-of-stores.ll
Modified:
    llvm/trunk/lib/Transforms/Utils/PromoteMemoryToRegister.cpp

Modified: llvm/trunk/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/PromoteMemoryToRegister.cpp?rev=334187&r1=334186&r2=334187&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/PromoteMemoryToRegister.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/PromoteMemoryToRegister.cpp Thu Jun  7 04:09:05 2018
@@ -511,6 +511,11 @@ static bool promoteSingleBlockAlloca(All
           !isKnownNonZero(ReplVal, DL, 0, AC, LI, &DT))
         addAssumeNonNull(AC, LI);
 
+      // If the replacement value is the load, this must occur in unreachable
+      // code.
+      if (ReplVal == LI)
+        ReplVal = UndefValue::get(LI->getType());
+
       LI->replaceAllUsesWith(ReplVal);
     }
 

Added: llvm/trunk/test/Transforms/Mem2Reg/pr37632-unreachable-list-of-stores.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/Mem2Reg/pr37632-unreachable-list-of-stores.ll?rev=334187&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/Mem2Reg/pr37632-unreachable-list-of-stores.ll (added)
+++ llvm/trunk/test/Transforms/Mem2Reg/pr37632-unreachable-list-of-stores.ll Thu Jun  7 04:09:05 2018
@@ -0,0 +1,20 @@
+; RUN: opt -mem2reg < %s -S | FileCheck %s
+
+
+; CHECK-LABEL: void @patatino()
+; CHECK-NEXT: ret void
+
+; CHECK-LABEL: cantreachme:
+; CHECK-NEXT: %dec = add nsw i32 undef, -1
+; CHECK-NEXT: br label %cantreachme
+
+define void @patatino() {
+  %a = alloca i32, align 4
+  ret void
+cantreachme:
+  %dec = add nsw i32 %tmp, -1
+  store i32 %dec, i32* %a
+  store i32 %tmp, i32* %a
+  %tmp = load i32, i32* %a
+  br label %cantreachme
+}