[HLSL] Move FNeg legalization to the DXILLegalization pass (#140942)

Fixes #137685

Author: sumitsays

llvm/lib/Target/DirectX/DXILLegalizePass.cpp

@@ -405,6 +405,20 @@ static void removeMemSet(Instruction &I,
   ToRemove.push_back(CI);
 }
 
+static void updateFnegToFsub(Instruction &I,
+                             SmallVectorImpl<Instruction *> &ToRemove,
+                             DenseMap<Value *, Value *> &) {
+  const Intrinsic::ID ID = I.getOpcode();
+  if (ID != Instruction::FNeg)
+    return;
+
+  IRBuilder<> Builder(&I);
+  Value *In = I.getOperand(0);
+  Value *Zero = ConstantFP::get(In->getType(), -0.0);
+  I.replaceAllUsesWith(Builder.CreateFSub(Zero, In));
+  ToRemove.push_back(&I);
+}
+
 namespace {
 class DXILLegalizationPipeline {
 
@@ -438,6 +452,7 @@ class DXILLegalizationPipeline {
     LegalizationPipeline.push_back(legalizeFreeze);
     LegalizationPipeline.push_back(legalizeMemCpy);
     LegalizationPipeline.push_back(removeMemSet);
+    LegalizationPipeline.push_back(updateFnegToFsub);
   }
 };
 

llvm/lib/Target/DirectX/DXILPrepare.cpp

@@ -204,15 +204,6 @@ class DXILPrepareModule : public ModulePass {
 
           I.dropUnknownNonDebugMetadata(DXILCompatibleMDs);
 
-          if (I.getOpcode() == Instruction::FNeg) {
-            Builder.SetInsertPoint(&I);
-            Value *In = I.getOperand(0);
-            Value *Zero = ConstantFP::get(In->getType(), -0.0);
-            I.replaceAllUsesWith(Builder.CreateFSub(Zero, In));
-            I.eraseFromParent();
-            continue;
-          }
-
           // Emtting NoOp bitcast instructions allows the ValueEnumerator to be
           // unmodified as it reserves instruction IDs during contruction.
           if (auto LI = dyn_cast<LoadInst>(&I)) {

llvm/test/CodeGen/DirectX/fneg-conversion.ll

@@ -0,0 +1,23 @@
+; RUN: opt -S -passes='dxil-legalize' -mtriple=dxil-pc-shadermodel6.3-library %s | FileCheck %s
+
+define float @negateF(float %x) {
+; CHECK-LABEL: define float @negateF(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[Y:%.*]] = fsub float -0.000000e+00, [[X]]
+; CHECK-NEXT:    ret float [[Y]]
+entry:  
+  %y = fneg float %x
+  ret float %y
+}
+
+define double @negateD(double %x) {
+; CHECK-LABEL: define double @negateD(
+; CHECK-SAME: double [[X:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[Y:%.*]] = fsub double -0.000000e+00, [[X]]
+; CHECK-NEXT:    ret double [[Y]]
+entry:  
+  %y = fneg double %x
+  ret double %y
+}