[llvm] r219434 - [Reassociate] Don't canonicalize X - undef to X + (-undef).

[Chad Rosier]

Author: mcrosier
Date: Thu Oct  9 15:06:29 2014
New Revision: 219434

URL: http://llvm.org/viewvc/llvm-project?rev=219434&view=rev
Log:
[Reassociate] Don't canonicalize X - undef to X + (-undef).

Phabricator Revision: http://reviews.llvm.org/D5674
PR21205

Added:
    llvm/trunk/test/Transforms/Reassociate/pr21205.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp?rev=219434&r1=219433&r2=219434&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp Thu Oct  9 15:06:29 2014
@@ -967,6 +967,10 @@ static bool ShouldBreakUpSubtract(Instru
   if (BinaryOperator::isNeg(Sub) || BinaryOperator::isFNeg(Sub))
     return false;
 
+  // Don't breakup X - undef.
+  if (isa<UndefValue>(Sub->getOperand(1)))
+    return false;
+
   // Don't bother to break this up unless either the LHS is an associable add or
   // subtract or if this is only used by one.
   Value *V0 = Sub->getOperand(0);

Added: llvm/trunk/test/Transforms/Reassociate/pr21205.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/Reassociate/pr21205.ll?rev=219434&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/Reassociate/pr21205.ll (added)
+++ llvm/trunk/test/Transforms/Reassociate/pr21205.ll Thu Oct  9 15:06:29 2014
@@ -0,0 +1,21 @@
+; RUN: opt -reassociate -S < %s | FileCheck %s
+; PR21205
+
+ at a = common global i32 0, align 4
+ at b = common global i32 0, align 4
+
+; Don't canonicalize %conv - undef into %conv + (-undef).
+; CHECK-LABEL: @test1
+; CHECK: %sub = fsub fast float %conv, undef
+; CHECK: %sub1 = fadd fast float %sub, -1.000000e+00
+
+define i32 @test1() {
+entry:
+  %0 = load i32* @a, align 4
+  %conv = sitofp i32 %0 to float
+  %sub = fsub fast float %conv, undef
+  %sub1 = fadd fast float %sub, -1.000000e+00
+  %conv2 = fptosi float %sub1 to i32
+  store i32 %conv2, i32* @b, align 4
+  ret i32 undef
+}