InstCombine: Fold fneg (copysign x, y) -> copysign x, (fneg y)

Author: arsenm

llvm/include/llvm/IR/IRBuilder.h

@@ -944,6 +944,14 @@ class IRBuilderBase {
     return CreateBinaryIntrinsic(Intrinsic::maximum, LHS, RHS, nullptr, Name);
   }
 
+  /// Create call to the copysign intrinsic.
+  CallInst *CreateCopySign(Value *LHS, Value *RHS,
+                           Instruction *FMFSource = nullptr,
+                           const Twine &Name = "") {
+    return CreateBinaryIntrinsic(Intrinsic::copysign, LHS, RHS, FMFSource,
+                                 Name);
+  }
+
   /// Create a call to the arithmetic_fence intrinsic.
   CallInst *CreateArithmeticFence(Value *Val, Type *DstType,
                                   const Twine &Name = "") {

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -2436,9 +2436,13 @@ Instruction *InstCombinerImpl::visitFNeg(UnaryOperator &I) {
   if (Instruction *R = hoistFNegAboveFMulFDiv(I, Builder))
     return R;
 
+  Value *OneUse;
+  if (!match(Op, m_OneUse(m_Value(OneUse))))
+    return nullptr;
+
   // Try to eliminate fneg if at least 1 arm of the select is negated.
   Value *Cond;
-  if (match(Op, m_OneUse(m_Select(m_Value(Cond), m_Value(X), m_Value(Y))))) {
+  if (match(OneUse, m_Select(m_Value(Cond), m_Value(X), m_Value(Y)))) {
     // Unlike most transforms, this one is not safe to propagate nsz unless
     // it is present on the original select. We union the flags from the select
     // and fneg and then remove nsz if needed.
@@ -2470,6 +2474,21 @@ Instruction *InstCombinerImpl::visitFNeg(UnaryOperator &I) {
     }
   }
 
+  // fneg (copysign x, y) -> copysign x, (fneg y)
+  if (match(OneUse, m_CopySign(m_Value(X), m_Value(Y)))) {
+    // The source copysign has an additional value input, so we can't propagate
+    // flags the copysign doesn't also have.
+    FastMathFlags FMF = I.getFastMathFlags();
+    FMF &= cast<FPMathOperator>(OneUse)->getFastMathFlags();
+
+    IRBuilder<>::FastMathFlagGuard FMFGuard(Builder);
+    Builder.setFastMathFlags(FMF);
+
+    Value *NegY = Builder.CreateFNeg(Y);
+    Value *NewCopySign = Builder.CreateCopySign(X, NegY);
+    return replaceInstUsesWith(I, NewCopySign);
+  }
+
   return nullptr;
 }
 

llvm/test/Transforms/InstCombine/copysign-fneg-fabs.ll

@@ -68,9 +68,9 @@ define half @copysign_fneg_fabs_y(half %x, half %y) {
 
 define half @fneg_copysign(half %x, half %y) {
 ; CHECK-LABEL: @fneg_copysign(
-; CHECK-NEXT:    [[COPYSIGN:%.*]] = call half @llvm.copysign.f16(half [[X:%.*]], half [[Y:%.*]])
-; CHECK-NEXT:    [[FNEG_COPYSIGN:%.*]] = fneg half [[COPYSIGN]]
-; CHECK-NEXT:    ret half [[FNEG_COPYSIGN]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fneg half [[Y:%.*]]
+; CHECK-NEXT:    [[TMP2:%.*]] = call half @llvm.copysign.f16(half [[X:%.*]], half [[TMP1]])
+; CHECK-NEXT:    ret half [[TMP2]]
 ;
   %copysign = call half @llvm.copysign.f16(half %x, half %y)
   %fneg.copysign = fneg half %copysign
@@ -102,9 +102,9 @@ define half @fabs_copysign(half %x, half %y) {
 
 define <2 x half> @fneg_copysign_vector(<2 x half> %x, <2 x half> %y) {
 ; CHECK-LABEL: @fneg_copysign_vector(
-; CHECK-NEXT:    [[COPYSIGN:%.*]] = call <2 x half> @llvm.copysign.v2f16(<2 x half> [[X:%.*]], <2 x half> [[Y:%.*]])
-; CHECK-NEXT:    [[FNEG_COPYSIGN:%.*]] = fneg <2 x half> [[COPYSIGN]]
-; CHECK-NEXT:    ret <2 x half> [[FNEG_COPYSIGN]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fneg <2 x half> [[Y:%.*]]
+; CHECK-NEXT:    [[TMP2:%.*]] = call <2 x half> @llvm.copysign.v2f16(<2 x half> [[X:%.*]], <2 x half> [[TMP1]])
+; CHECK-NEXT:    ret <2 x half> [[TMP2]]
 ;
   %copysign = call <2 x half> @llvm.copysign.v2f16(<2 x half> %x, <2 x half> %y)
   %fneg.copysign = fneg <2 x half> %copysign
@@ -135,9 +135,9 @@ define <2 x half> @fabs_copysign_vector(<2 x half> %x, <2 x half> %y) {
 
 define half @fneg_copysign_flags(half %x, half %y) {
 ; CHECK-LABEL: @fneg_copysign_flags(
-; CHECK-NEXT:    [[COPYSIGN:%.*]] = call nnan nsz half @llvm.copysign.f16(half [[X:%.*]], half [[Y:%.*]])
-; CHECK-NEXT:    [[FNEG_COPYSIGN:%.*]] = fneg ninf nsz half [[COPYSIGN]]
-; CHECK-NEXT:    ret half [[FNEG_COPYSIGN]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fneg nsz half [[Y:%.*]]
+; CHECK-NEXT:    [[TMP2:%.*]] = call nsz half @llvm.copysign.f16(half [[X:%.*]], half [[TMP1]])
+; CHECK-NEXT:    ret half [[TMP2]]
 ;
   %copysign = call nnan nsz half @llvm.copysign.f16(half %x, half %y)
   %fneg.copysign = fneg ninf nsz half %copysign
@@ -159,9 +159,9 @@ define half @fneg_fabs_copysign_flags(half %x, half %y) {
 ; Make sure we don't break things by polluting copysign with nsz
 define half @fneg_nsz_copysign(half %x, half %y) {
 ; CHECK-LABEL: @fneg_nsz_copysign(
-; CHECK-NEXT:    [[COPYSIGN:%.*]] = call half @llvm.copysign.f16(half [[X:%.*]], half [[Y:%.*]])
-; CHECK-NEXT:    [[FNEG_COPYSIGN:%.*]] = fneg nsz half [[COPYSIGN]]
-; CHECK-NEXT:    ret half [[FNEG_COPYSIGN]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fneg half [[Y:%.*]]
+; CHECK-NEXT:    [[TMP2:%.*]] = call half @llvm.copysign.f16(half [[X:%.*]], half [[TMP1]])
+; CHECK-NEXT:    ret half [[TMP2]]
 ;
   %copysign = call half @llvm.copysign.f16(half %x, half %y)
   %fneg.copysign = fneg nsz half %copysign

llvm/test/Transforms/InstCombine/unordered-compare-and-ordered.ll

@@ -480,8 +480,8 @@ define i1 @fcmp_ord_and_copysign_fneg_ueq(half %x, half %y, half %z) {
 
 define i1 @fcmp_ord_and_fneg_copysign_ueq(half %x, half %y, half %z) {
 ; CHECK-LABEL: @fcmp_ord_and_fneg_copysign_ueq(
-; CHECK-NEXT:    [[COPYSIGN_X_Y:%.*]] = call half @llvm.copysign.f16(half [[X:%.*]], half [[Z:%.*]])
-; CHECK-NEXT:    [[FNEG_COPYSIGN:%.*]] = fneg half [[COPYSIGN_X_Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fneg half [[Z:%.*]]
+; CHECK-NEXT:    [[FNEG_COPYSIGN:%.*]] = call half @llvm.copysign.f16(half [[X:%.*]], half [[TMP1]])
 ; CHECK-NEXT:    [[ORD:%.*]] = fcmp ord half [[X]], 0xH0000
 ; CHECK-NEXT:    [[UEQ:%.*]] = fcmp ueq half [[FNEG_COPYSIGN]], [[Y:%.*]]
 ; CHECK-NEXT:    [[AND:%.*]] = and i1 [[ORD]], [[UEQ]]