[llvm] r273144 - Avoid output indeterminism between GCC and Clang builds.

[Patrik Hagglund via llvm-commits]

Author: patha
Date: Mon Jun 20 05:19:00 2016
New Revision: 273144

URL: http://llvm.org/viewvc/llvm-project?rev=273144&view=rev
Log:
Avoid output indeterminism between GCC and Clang builds.

Remove dependency of the evalution order of function arguments, which
is unspecified.

The following test previously failed when built with GCC (but succeded
when built with Clang):

  ; RUN: opt -sroa -S < %s | FileCheck %s

  target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
  target triple = "x86_64-unknown-linux-gnu"

  %A = type {i16}

  @a = global %A* null
  @b = global i16 0

  ; CHECK-LABEL: @f1(
  ; CHECK: alloca %A
  ; CHECK-NEXT: extractvalue %A
  ; CHECK-NEXT: getelementptr inbounds %A

  define void @f1 (%A %a) {
    %1 = alloca %A
    store %A %a, %A* %1
    %2 = load i16, i16* @b
    %3 = icmp ne i16 %2, 0
    br i1 %3, label %bb1, label %bb2
  bb1:
    store %A* %1, %A** @a
    br label %bb2
  bb2:
    ret void
  }

Patch by David Stenberg.

Differential Revision: http://reviews.llvm.org/D21226

Modified:
    llvm/trunk/lib/Transforms/Scalar/SROA.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/SROA.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/SROA.cpp?rev=273144&r1=273143&r2=273144&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/SROA.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/SROA.cpp Mon Jun 20 05:19:00 2016
@@ -3107,9 +3107,14 @@ private:
     void emitFunc(Type *Ty, Value *&Agg, const Twine &Name) {
       assert(Ty->isSingleValueType());
       // Extract the single value and store it using the indices.
-      Value *Store = IRB.CreateStore(
-          IRB.CreateExtractValue(Agg, Indices, Name + ".extract"),
-          IRB.CreateInBoundsGEP(nullptr, Ptr, GEPIndices, Name + ".gep"));
+      //
+      // The gep and extractvalue values are factored out of the CreateStore
+      // call to make the output independent of the argument evaluation order.
+      Value *ExtractValue = IRB.CreateExtractValue(Agg, Indices,
+        Name + ".extract");
+      Value *InBoundsGEP = IRB.CreateInBoundsGEP(nullptr, Ptr, GEPIndices,
+        Name + ".gep");
+      Value *Store = IRB.CreateStore(ExtractValue, InBoundsGEP);
       (void)Store;
       DEBUG(dbgs() << "          to: " << *Store << "\n");
     }