[InstSimplify] fold fsub+fsub with common operand

llvm-svn: 339171

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 02137a51844a5178551d05a71eed764376b62840..d0794364a7351cafa7c199a762f63ca4ccd4325c 100644 (file)
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4396,6 +4396,11 @@ static Value *SimplifyFSubInst(Value *Op0, Value *Op1, FastMathFlags FMF,
   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;
 }
 

diff --git a/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll b/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
index 0481ee45651428825963cbae1fa945dfa5d47dc9..6350c233a932dc2590b1c5b4d5b61a0fd1e13094 100644 (file)
--- a/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
+++ b/llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
@@ -737,9 +737,7 @@ define float @maxnum_x_y_maxnum_z(float %x, float %y, float %z) {
 
 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 %x, float %y) {
 
 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