[llvm] r339171 - [InstSimplify] fold fsub+fsub with common operand

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Tue Aug  7 13:14:27 2018
New Revision: 339171

URL: http://llvm.org/viewvc/llvm-project?rev=339171&view=rev
Log:
[InstSimplify] fold fsub+fsub with common operand

Modified:
    llvm/trunk/lib/Analysis/InstructionSimplify.cpp
    llvm/trunk/test/Transforms/InstSimplify/floating-point-arithmetic.ll

Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=339171&r1=339170&r2=339171&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Tue Aug  7 13:14:27 2018
@@ -4396,6 +4396,11 @@ static Value *SimplifyFSubInst(Value *Op
   if (FMF.noNaNs() && Op0 == Op1)
     return Constant::getNullValue(Op0->getType());
 
+  // Y - (Y - X) --> X
+  if (FMF.noSignedZeros() && FMF.allowReassoc() &&
+      match(Op1, m_FSub(m_Specific(Op0), m_Value(X))))
+    return X;
+
   return nullptr;
 }
 

Modified: llvm/trunk/test/Transforms/InstSimplify/floating-point-arithmetic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/floating-point-arithmetic.ll?rev=339171&r1=339170&r2=339171&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/floating-point-arithmetic.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/floating-point-arithmetic.ll Tue Aug  7 13:14:27 2018
@@ -737,9 +737,7 @@ define float @maxnum_x_y_maxnum_z(float
 
 define float @fsub_fsub_common_op(float %x, float %y) {
 ; CHECK-LABEL: @fsub_fsub_common_op(
-; CHECK-NEXT:    [[S:%.*]] = fsub float [[Y:%.*]], [[X:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = fsub reassoc nsz float [[Y]], [[S]]
-; CHECK-NEXT:    ret float [[R]]
+; CHECK-NEXT:    ret float [[X:%.*]]
 ;
   %s = fsub float %y, %x
   %r = fsub reassoc nsz float %y, %s
@@ -748,9 +746,7 @@ define float @fsub_fsub_common_op(float
 
 define <2 x float> @fsub_fsub_common_op_vec(<2 x float> %x, <2 x float> %y) {
 ; CHECK-LABEL: @fsub_fsub_common_op_vec(
-; CHECK-NEXT:    [[S:%.*]] = fsub <2 x float> [[Y:%.*]], [[X:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = fsub reassoc nsz <2 x float> [[Y]], [[S]]
-; CHECK-NEXT:    ret <2 x float> [[R]]
+; CHECK-NEXT:    ret <2 x float> [[X:%.*]]
 ;
   %s = fsub <2 x float> %y, %x
   %r = fsub reassoc nsz <2 x float> %y, %s