[PATCH] D62077: [InstSimplify] Teach fsub -0.0, (fneg X) ==> X about unary fneg

[Cameron McInally via Phabricator via llvm-commits]

cameron.mcinally created this revision.
cameron.mcinally added reviewers: spatel, arsenm, kpn, craig.topper, andrew.w.kaylor.
Herald added subscribers: llvm-commits, hiraditya, wdng.
Herald added a project: LLVM.

One incoming comment inline about a tough decision...


Repository:
  rL LLVM

https://reviews.llvm.org/D62077

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


Index: llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
+++ llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll
@@ -31,9 +31,7 @@
 ; fsub -0.0, (fneg X) ==> X
 define float @fneg_x(float %a) {
 ; CHECK-LABEL: @fneg_x(
-; CHECK-NEXT:    %t1 = fneg float %a
-; CHECK-NEXT:    %ret = fsub float -0.000000e+00, %t1
-; CHECK-NEXT:    ret float %ret
+; CHECK-NEXT:    ret float [[A:%.*]]
 ;
   %t1 = fneg float %a
   %ret = fsub float -0.0, %t1
@@ -51,9 +49,7 @@
 
 define <2 x float> @fneg_x_vec(<2 x float> %a) {
 ; CHECK-LABEL: @fneg_x_vec(
-; CHECK-NEXT:    %t1 = fneg <2 x float> %a
-; CHECK-NEXT:    %ret = fsub <2 x float> <float -0.000000e+00, float -0.000000e+00>, %t1
-; CHECK-NEXT:    ret <2 x float> %ret
+; CHECK-NEXT:    ret <2 x float> [[A:%.*]]
 ;
   %t1 = fneg <2 x float> %a
   %ret = fsub <2 x float> <float -0.0, float -0.0>, %t1
@@ -71,9 +67,7 @@
 
 define <2 x float> @fneg_x_vec_undef_elts(<2 x float> %a) {
 ; CHECK-LABEL: @fneg_x_vec_undef_elts(
-; CHECK-NEXT:    %t1 = fneg <2 x float> %a
-; CHECK-NEXT:    %ret = fsub <2 x float> <float -0.000000e+00, float undef>, %t1
-; CHECK-NEXT:    ret <2 x float> %ret
+; CHECK-NEXT:    ret <2 x float> [[A:%.*]]
 ;
   %t1 = fneg <2 x float> %a
   %ret = fsub <2 x float> <float -0.0, float undef>, %t1
Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4394,9 +4394,10 @@
     return Op0;
 
   // fsub -0.0, (fsub -0.0, X) ==> X
+  // fsub -0.0, (fneg X) ==> X
   Value *X;
   if (match(Op0, m_NegZeroFP()) &&
-      match(Op1, m_FSub(m_NegZeroFP(), m_Value(X))))
+      match(Op1, m_FNeg(m_Value(X))))
     return X;
 
   // fsub 0.0, (fsub 0.0, X) ==> X if signed zeros are ignored.


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