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

Differential Revision: https://reviews.llvm.org/D61916

llvm-svn: 360777
```
```diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index febc1d5..770fdf9 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
```
```@@ -4316,16 +4316,22 @@
(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
index 08fb611..5f981ed 100644
--- a/llvm/test/Transforms/InstSimplify/fast-math.ll
+++ b/llvm/test/Transforms/InstSimplify/fast-math.ll
```
```@@ -56,8 +56,8 @@

; -X + X --> 0.0 (with nnan on the fadd)

; CHECK-NEXT:    ret float 0.000000e+00
;
%negx = fsub float -0.0, %x
@@ -65,10 +65,19 @@
ret float %r
}

+; 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) {
+define <2 x float> @fadd_binary_fnegx_commute_vec(<2 x float> %x) {
; CHECK-NEXT:    ret <2 x float> zeroinitializer
;
%negx = fsub <2 x float> <float -0.0, float -0.0>, %x
@@ -76,6 +85,15 @@
ret <2 x float> %r
}

+define <2 x float> @fadd_unary_fnegx_commute_vec(<2 x float> %x) {