Teach InstSimplify -X + X --> 0.0 about unary FNeg

mcinally · mcinally · commit 0c82d9b5a2e2 · 2019-05-15T14:31:33.000Z
Differential Revision: https://reviews.llvm.org/D61916 llvm-svn: 360777
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4316,16 +4316,22 @@ static Value *SimplifyFAddInst(Value *Op0, Value *Op1, FastMathFlags FMF,
       (FMF.noSignedZeros() || CannotBeNegativeZero(Op0, Q.TLI)))
     return Op0;
 
-  // With nnan: (+/-0.0 - X) + X --> 0.0 (and commuted variant)
+  // With nnan: -X + X --> 0.0 (and commuted variant)
   // We don't have to explicitly exclude infinities (ninf): INF + -INF == NaN.
   // Negative zeros are allowed because we always end up with positive zero:
   // X = -0.0: (-0.0 - (-0.0)) + (-0.0) == ( 0.0) + (-0.0) == 0.0
   // X = -0.0: ( 0.0 - (-0.0)) + (-0.0) == ( 0.0) + (-0.0) == 0.0
   // X =  0.0: (-0.0 - ( 0.0)) + ( 0.0) == (-0.0) + ( 0.0) == 0.0
   // X =  0.0: ( 0.0 - ( 0.0)) + ( 0.0) == ( 0.0) + ( 0.0) == 0.0
-  if (FMF.noNaNs() && (match(Op0, m_FSub(m_AnyZeroFP(), m_Specific(Op1))) ||
-                       match(Op1, m_FSub(m_AnyZeroFP(), m_Specific(Op0)))))
-    return ConstantFP::getNullValue(Op0->getType());
+  if (FMF.noNaNs()) {
+    if (match(Op0, m_FSub(m_AnyZeroFP(), m_Specific(Op1))) ||
+        match(Op1, m_FSub(m_AnyZeroFP(), m_Specific(Op0))))
+      return ConstantFP::getNullValue(Op0->getType());
+
+    if (match(Op0, m_FNeg(m_Specific(Op1))) ||
+        match(Op1, m_FNeg(m_Specific(Op0))))
+      return ConstantFP::getNullValue(Op0->getType());
+  }
 
   // (X - Y) + Y --> X
   // Y + (X - Y) --> X
diff --git a/llvm/test/Transforms/InstSimplify/fast-math.ll b/llvm/test/Transforms/InstSimplify/fast-math.ll
@@ -56,26 +56,44 @@ define float @no_mul_zero_3(float %a) {
 
 ; -X + X --> 0.0 (with nnan on the fadd)
 
-define float @fadd_fnegx(float %x) {
-; CHECK-LABEL: @fadd_fnegx(
+define float @fadd_binary_fnegx(float %x) {
+; CHECK-LABEL: @fadd_binary_fnegx(
 ; CHECK-NEXT:    ret float 0.000000e+00
 ;
   %negx = fsub float -0.0, %x
   %r = fadd nnan float %negx, %x
   ret float %r
 }
 
+define float @fadd_unary_fnegx(float %x) {
+; CHECK-LABEL: @fadd_unary_fnegx(
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+  %negx = fneg float %x
+  %r = fadd nnan float %negx, %x
+  ret float %r
+}
+
 ; X + -X --> 0.0 (with nnan on the fadd)
 
-define <2 x float> @fadd_fnegx_commute_vec(<2 x float> %x) {
-; CHECK-LABEL: @fadd_fnegx_commute_vec(
+define <2 x float> @fadd_binary_fnegx_commute_vec(<2 x float> %x) {
+; CHECK-LABEL: @fadd_binary_fnegx_commute_vec(
 ; CHECK-NEXT:    ret <2 x float> zeroinitializer
 ;
   %negx = fsub <2 x float> <float -0.0, float -0.0>, %x
   %r = fadd nnan <2 x float> %x, %negx
   ret <2 x float> %r
 }
 
+define <2 x float> @fadd_unary_fnegx_commute_vec(<2 x float> %x) {
+; CHECK-LABEL: @fadd_unary_fnegx_commute_vec(
+; CHECK-NEXT:    ret <2 x float> zeroinitializer
+;
+  %negx = fneg <2 x float> %x
+  %r = fadd nnan <2 x float> %x, %negx
+  ret <2 x float> %r
+}
+
 define <2 x float> @fadd_fnegx_commute_vec_undef(<2 x float> %x) {
 ; CHECK-LABEL: @fadd_fnegx_commute_vec_undef(
 ; CHECK-NEXT:    ret <2 x float> zeroinitializer
