[InstCombine] sink FP negation of operands through select

rotateright · rotateright · commit fe9414d0ccbf · 2019-05-06T20:34:05.000Z
We don't always get this: Cond ? -X : -Y --> -(Cond ? X : Y) ...even with the legacy IR form of fneg in the case with extra uses, and we miss matching with the newer 'fneg' instruction because we are expecting binops through the rest of the path. Differential Revision: https://reviews.llvm.org/D61604 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@360075 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineSelect.cpp b/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -333,6 +333,18 @@ Instruction *InstCombiner::foldSelectOpOp(SelectInst &SI, Instruction *TI,
                             TI->getType());
   }
 
+  // Cond ? -X : -Y --> -(Cond ? X : Y)
+  Value *X, *Y;
+  if (match(TI, m_FNeg(m_Value(X))) && match(FI, m_FNeg(m_Value(Y))) &&
+      (TI->hasOneUse() || FI->hasOneUse())) {
+    Value *NewSel = Builder.CreateSelect(Cond, X, Y, SI.getName() + ".v", &SI);
+    // TODO: Remove the hack for the binop form when the unary op is optimized
+    //       properly with all IR passes.
+    if (TI->getOpcode() != Instruction::FNeg)
+      return BinaryOperator::CreateFNegFMF(NewSel, cast<BinaryOperator>(TI));
+    return UnaryOperator::CreateFNeg(NewSel);
+  }
+
   // Only handle binary operators (including two-operand getelementptr) with
   // one-use here. As with the cast case above, it may be possible to relax the
   // one-use constraint, but that needs be examined carefully since it may not
diff --git a/test/Transforms/InstCombine/fneg.ll b/test/Transforms/InstCombine/fneg.ll
@@ -161,9 +161,8 @@ define <4 x double> @fdiv_op0_constant_fneg_vec(<4 x double> %x) {
 
 define <2 x double> @fneg_fneg_sel(<2 x double> %x, <2 x double> %y, i1 %cond) {
 ; CHECK-LABEL: @fneg_fneg_sel(
-; CHECK-NEXT:    [[N1:%.*]] = fneg <2 x double> [[X:%.*]]
-; CHECK-NEXT:    [[N2:%.*]] = fneg <2 x double> [[Y:%.*]]
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND:%.*]], <2 x double> [[N1]], <2 x double> [[N2]]
+; CHECK-NEXT:    [[SEL_V:%.*]] = select i1 [[COND:%.*]], <2 x double> [[X:%.*]], <2 x double> [[Y:%.*]]
+; CHECK-NEXT:    [[SEL:%.*]] = fneg <2 x double> [[SEL_V]]
 ; CHECK-NEXT:    ret <2 x double> [[SEL]]
 ;
   %n1 = fneg <2 x double> %x
@@ -178,8 +177,8 @@ define float @fneg_fneg_sel_extra_use1(float %x, float %y, i1 %cond) {
 ; CHECK-LABEL: @fneg_fneg_sel_extra_use1(
 ; CHECK-NEXT:    [[N1:%.*]] = fneg float [[X:%.*]]
 ; CHECK-NEXT:    call void @use(float [[N1]])
-; CHECK-NEXT:    [[N2:%.*]] = fneg float [[Y:%.*]]
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND:%.*]], float [[N1]], float [[N2]]
+; CHECK-NEXT:    [[SEL_V:%.*]] = select i1 [[COND:%.*]], float [[X]], float [[Y:%.*]]
+; CHECK-NEXT:    [[SEL:%.*]] = fneg float [[SEL_V]]
 ; CHECK-NEXT:    ret float [[SEL]]
 ;
   %n1 = fneg float %x
@@ -191,10 +190,10 @@ define float @fneg_fneg_sel_extra_use1(float %x, float %y, i1 %cond) {
 
 define float @fneg_fneg_sel_extra_use2(float %x, float %y, i1 %cond) {
 ; CHECK-LABEL: @fneg_fneg_sel_extra_use2(
-; CHECK-NEXT:    [[N1:%.*]] = fneg float [[X:%.*]]
 ; CHECK-NEXT:    [[N2:%.*]] = fneg float [[Y:%.*]]
 ; CHECK-NEXT:    call void @use(float [[N2]])
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND:%.*]], float [[N1]], float [[N2]]
+; CHECK-NEXT:    [[SEL_V:%.*]] = select i1 [[COND:%.*]], float [[X:%.*]], float [[Y]]
+; CHECK-NEXT:    [[SEL:%.*]] = fneg float [[SEL_V]]
 ; CHECK-NEXT:    ret float [[SEL]]
 ;
   %n1 = fneg float %x
@@ -210,8 +209,8 @@ define float @fsub_fsub_sel_extra_use1(float %x, float %y, i1 %cond) {
 ; CHECK-LABEL: @fsub_fsub_sel_extra_use1(
 ; CHECK-NEXT:    [[N1:%.*]] = fsub float -0.000000e+00, [[X:%.*]]
 ; CHECK-NEXT:    call void @use(float [[N1]])
-; CHECK-NEXT:    [[N2:%.*]] = fsub float -0.000000e+00, [[Y:%.*]]
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND:%.*]], float [[N1]], float [[N2]]
+; CHECK-NEXT:    [[SEL_V:%.*]] = select i1 [[COND:%.*]], float [[X]], float [[Y:%.*]]
+; CHECK-NEXT:    [[SEL:%.*]] = fsub float -0.000000e+00, [[SEL_V]]
 ; CHECK-NEXT:    ret float [[SEL]]
 ;
   %n1 = fsub float -0.0, %x
