[DirectX] Make DXILOpLowering responsible for cleaning up dead intrinsics

This moves the responsibility for cleaning up dead intrinsics from
DXILFinalizeLinkage to DXILOpLowering, and moves DXILFinalizeLinkage back to
it's pre-llvm#136244 place in the pipeline. Doing this avoids issues with DXIL
passes running on obviously dead code, and makes it more clear what
DXILFinalizeLinkage is really doing.

This also helps with the story for llvm#134260, as cleaning up dead intrinsics
doesn't make sense if this becomes a more generic pass.

Note that test/CodeGen/DirectX/remove-dead-intriniscs.ll already covers most of
the testing here. It'd be nice to have something that catches the regression
from changing the pass ordering but I couldn't come up with anything that
wouldn't be incredibly fragile.

Fixes llvm#138180.

Author: bogner

llvm/lib/Target/DirectX/DXILFinalizeLinkage.cpp

@@ -36,14 +36,6 @@ static bool finalizeLinkage(Module &M) {
       M.getFunctionList().erase(F);
   }
 
-  // Do a pass over intrinsics that are no longer used and remove them.
-  Funcs.clear();
-  for (Function &F : M.functions())
-    if (F.isIntrinsic() && F.use_empty())
-      Funcs.push_back(&F);
-  for (Function *F : Funcs)
-    F->eraseFromParent();
-
   return false;
 }
 

llvm/lib/Target/DirectX/DXILOpLowering.cpp

@@ -756,14 +756,20 @@ class OpLowerer {
       case Intrinsic::lifetime_start:
       case Intrinsic::lifetime_end:
       case Intrinsic::not_intrinsic:
+        if (F.use_empty())
+          F.eraseFromParent();
         continue;
-      default: {
-        SmallString<128> Msg =
-            formatv("Unsupported intrinsic {0} for DXIL lowering", F.getName());
-        M.getContext().emitError(Msg);
-        HasErrors |= true;
+      default:
+        if (F.use_empty())
+          F.eraseFromParent();
+        else {
+          SmallString<128> Msg = formatv(
+              "Unsupported intrinsic {0} for DXIL lowering", F.getName());
+          M.getContext().emitError(Msg);
+          HasErrors |= true;
+        }
         break;
-      }
+
 #define DXIL_OP_INTRINSIC(OpCode, Intrin, ...)                                 \
   case Intrin:                                                                 \
     HasErrors |= replaceFunctionWithOp(                                        \

llvm/lib/Target/DirectX/DirectXTargetMachine.cpp

@@ -98,6 +98,7 @@ class DirectXPassConfig : public TargetPassConfig {
 
   FunctionPass *createTargetRegisterAllocator(bool) override { return nullptr; }
   void addCodeGenPrepare() override {
+    addPass(createDXILFinalizeLinkageLegacyPass());
     addPass(createDXILIntrinsicExpansionLegacyPass());
     addPass(createDXILCBufferAccessLegacyPass());
     addPass(createDXILDataScalarizationLegacyPass());
@@ -108,7 +109,6 @@ class DirectXPassConfig : public TargetPassConfig {
     addPass(createScalarizerPass(DxilScalarOptions));
     addPass(createDXILForwardHandleAccessesLegacyPass());
     addPass(createDXILLegalizeLegacyPass());
-    addPass(createDXILFinalizeLinkageLegacyPass());
     addPass(createDXILTranslateMetadataLegacyPass());
     addPass(createDXILOpLoweringLegacyPass());
     addPass(createDXILPrepareModulePass());

llvm/test/CodeGen/DirectX/llc-pipeline.ll

@@ -13,6 +13,7 @@
 ; CHECK-OBJ-NEXT: Create Garbage Collector Module Metadata
 
 ; CHECK-NEXT: ModulePass Manager
+; CHECK-NEXT:   DXIL Finalize Linkage
 ; CHECK-NEXT:   DXIL Intrinsic Expansion
 ; CHECK-NEXT:   DXIL CBuffer Access
 ; CHECK-NEXT:   DXIL Data Scalarization
@@ -23,7 +24,6 @@
 ; CHECK-NEXT:     Scalarize vector operations
 ; CHECK-NEXT:     DXIL Forward Handle Accesses
 ; CHECK-NEXT:     DXIL Legalizer
-; CHECK-NEXT:   DXIL Finalize Linkage
 ; CHECK-NEXT:   DXIL Resources Analysis
 ; CHECK-NEXT:   DXIL Module Metadata analysis
 ; CHECK-NEXT:   DXIL Shader Flag Analysis