InstCombine: fdiv -x, -y -> fdiv x, y

[arsenm]

ping

[majnemer]

LGTM

test/Transforms/InstCombine/fdiv.ll

62–69

This test does not provide additional coverage.

[arsenm]

test/Transforms/InstCombine/fdiv.ll

62–69

This checks that the fast math falls are preserved

[majnemer]

test/Transforms/InstCombine/fdiv.ll

62–69

Ah, right...

[arsenm]

r291611

lib/Transforms/InstCombine/InstCombineMulDivRem.cpp

if (AllowReassociate) {
     if (NewInst) {
       if (Instruction *T = dyn_cast<Instruction>(NewInst))
         T->setDebugLoc(I.getDebugLoc());
       SimpR->setFastMathFlags(I.getFastMathFlags());
       return SimpR;
     }
   }
 
+  Value *LHS;
+  Value *RHS;
+
+  // -x / -y -> x / y
+  if (match(Op0, m_FNeg(m_Value(LHS))) && match(Op1, m_FNeg(m_Value(RHS)))) {
+    I.setOperand(0, LHS);
+    I.setOperand(1, RHS);
+    return &I;
+  }
+
   return nullptr;
 }
 
 /// This function implements the transforms common to both integer remainder
 /// instructions (urem and srem). It is called by the visitors to those integer
 /// remainder instructions.
 /// @brief Common integer remainder transforms
 Instruction *InstCombiner::commonIRemTransforms(BinaryOperator &I) {

test/Transforms/InstCombine/fdiv.ll

 define float @test6(float %x, float %y, float %z) nounwind readnone ssp {
   %div1 = fdiv fast float %x, %y
   %div2 = fdiv fast float %z, %div1
   ret float %div2
 ; CHECK-LABEL: @test6(
 ; CHECK-NEXT: fmul fast
 ; CHECK-NEXT: fdiv fast
 }
+
+; CHECK-LABEL @fdiv_fneg_fneg(
+; CHECK: %div = fdiv float %x, %y
+define float @fdiv_fneg_fneg(float %x, float %y) {
+  %x.fneg = fsub float -0.0, %x
+  %y.fneg = fsub float -0.0, %y
+  %div = fdiv float %x.fneg, %y.fneg
+  ret float %div
+}
+
+; CHECK-LABEL @fdiv_fneg_fneg_fast(
+; CHECK: %div = fdiv fast float %x, %y
+define float @fdiv_fneg_fneg_fast(float %x, float %y) {
+  %x.fneg = fsub float -0.0, %x
+  %y.fneg = fsub float -0.0, %y
+  %div = fdiv fast float %x.fneg, %y.fneg
+  ret float %div
+}