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[HLSL] Change default linkage of HLSL functions to internal (#95331)
An HLSL function has internal linkage by default unless it is: 1. shader entry point function 2. marked with the `export` keyword (#92812) 3. patch constant function (not implemented yet) This PR adds a link-time pass `DXILFinalizeLinkage` that updates the linkage of functions to make sure only shader entry points and exported functions are visible from the module (have _program linkage_). All other functions will be updated to have internal linkage. Related spec update: microsoft/hlsl-specs#295 Fixes ##92071
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‎llvm/lib/Target/DirectX/CMakeLists.txt‎

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@@ -19,6 +19,7 @@ add_llvm_target(DirectXCodeGen
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DirectXSubtarget.cpp
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DirectXTargetMachine.cpp
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DXContainerGlobals.cpp
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DXILFinalizeLinkage.cpp
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DXILIntrinsicExpansion.cpp
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DXILMetadata.cpp
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DXILOpBuilder.cpp

‎llvm/lib/Target/DirectX/DXILFinalizeLinkage.cpp‎

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//===- DXILFinalizeLinkage.cpp - Finalize linkage of functions ------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "DXILFinalizeLinkage.h"
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#include "DirectX.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/GlobalValue.h"
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#include "llvm/IR/Metadata.h"
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#include "llvm/IR/Module.h"
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#define DEBUG_TYPE "dxil-finalize-linkage"
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using namespace llvm;
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static bool finalizeLinkage(Module &M) {
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SmallPtrSet<Function *, 8> EntriesAndExports;
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// Find all entry points and export functions
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for (Function &EF : M.functions()) {
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if (!EF.hasFnAttribute("hlsl.shader") && !EF.hasFnAttribute("hlsl.export"))
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continue;
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EntriesAndExports.insert(&EF);
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}
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for (Function &F : M.functions()) {
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if (F.getLinkage() == GlobalValue::ExternalLinkage &&
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!EntriesAndExports.contains(&F)) {
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F.setLinkage(GlobalValue::InternalLinkage);
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}
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}
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return false;
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}
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PreservedAnalyses DXILFinalizeLinkage::run(Module &M,
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ModuleAnalysisManager &AM) {
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if (finalizeLinkage(M))
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return PreservedAnalyses::none();
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return PreservedAnalyses::all();
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}
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bool DXILFinalizeLinkageLegacy::runOnModule(Module &M) {
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return finalizeLinkage(M);
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}
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char DXILFinalizeLinkageLegacy::ID = 0;
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INITIALIZE_PASS_BEGIN(DXILFinalizeLinkageLegacy, DEBUG_TYPE,
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"DXIL Finalize Linkage", false, false)
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INITIALIZE_PASS_END(DXILFinalizeLinkageLegacy, DEBUG_TYPE,
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"DXIL Finalize Linkage", false, false)
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ModulePass *llvm::createDXILFinalizeLinkageLegacyPass() {
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return new DXILFinalizeLinkageLegacy();
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}

‎llvm/lib/Target/DirectX/DXILFinalizeLinkage.h‎

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//===- DXILFinalizeLinkage.h - Finalize linkage of functions --------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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///
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/// DXILFinalizeLinkage pass updates the linkage of functions to make sure only
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/// shader entry points and exported functions are visible from the module (have
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/// program linkage). All other functions will be updated to have internal
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/// linkage.
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///
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TARGET_DIRECTX_DXILFINALIZELINKAGE_H
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#define LLVM_TARGET_DIRECTX_DXILFINALIZELINKAGE_H
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#include "llvm/IR/PassManager.h"
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#include "llvm/Pass.h"
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namespace llvm {
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class DXILFinalizeLinkage : public PassInfoMixin<DXILFinalizeLinkage> {
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public:
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PreservedAnalyses run(Module &M, ModuleAnalysisManager &);
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static bool isRequired() { return true; }
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};
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class DXILFinalizeLinkageLegacy : public ModulePass {
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public:
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DXILFinalizeLinkageLegacy() : ModulePass(ID) {}
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bool runOnModule(Module &M) override;
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static char ID; // Pass identification.
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};
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} // namespace llvm
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#endif // LLVM_TARGET_DIRECTX_DXILFINALIZELINKAGE_H

‎llvm/lib/Target/DirectX/DirectX.h‎

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@@ -63,6 +63,13 @@ void initializeDXContainerGlobalsPass(PassRegistry &);
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/// Pass for generating DXContainer part globals.
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ModulePass *createDXContainerGlobalsPass();
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/// Initializer for DXILFinalizeLinkage pass.
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void initializeDXILFinalizeLinkageLegacyPass(PassRegistry &);
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/// Pass to finalize linkage of functions.
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ModulePass *createDXILFinalizeLinkageLegacyPass();
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} // namespace llvm
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#endif // LLVM_LIB_TARGET_DIRECTX_DIRECTX_H

‎llvm/lib/Target/DirectX/DirectXTargetMachine.cpp‎

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@@ -48,6 +48,7 @@ extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeDirectXTarget() {
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initializeDXILTranslateMetadataPass(*PR);
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initializeDXILResourceMDWrapperPass(*PR);
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initializeShaderFlagsAnalysisWrapperPass(*PR);
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initializeDXILFinalizeLinkageLegacyPass(*PR);
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}
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class DXILTargetObjectFile : public TargetLoweringObjectFile {
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void addCodeGenPrepare() override {
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addPass(createDXILIntrinsicExpansionLegacyPass());
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addPass(createDXILOpLoweringLegacyPass());
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addPass(createDXILFinalizeLinkageLegacyPass());
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addPass(createDXILTranslateMetadataPass());
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addPass(createDXILPrepareModulePass());
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}

‎llvm/test/CodeGen/DirectX/conflicting-bitcast-insert.ll‎

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@@ -7,7 +7,7 @@ define i64 @test(ptr %p) {
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ret i64 %v
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}
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; CHECK: define i64 @test(ptr %p) {
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; CHECK: define internal i64 @test(ptr %p) {
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; CHECK-NEXT: %1 = bitcast ptr %p to ptr
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; CHECK-NEXT: store i32 0, ptr %1, align 4
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; CHECK-NEXT: %2 = bitcast ptr %p to ptr
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ret i64 %val
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}
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; CHECK: define i64 @testGEP(ptr %p) {
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; CHECK: define internal i64 @testGEP(ptr %p) {
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; CHECK-NEXT: %1 = bitcast ptr %p to ptr
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; CHECK-NEXT: %ptr = getelementptr i32, ptr %1, i32 4
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; CHECK-NEXT: %2 = bitcast ptr %p to ptr

‎llvm/test/CodeGen/DirectX/finalize_linkage.ll‎

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; RUN: opt -S -dxil-finalize-linkage -mtriple=dxil-unknown-shadermodel6.5-compute %s | FileCheck %s
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; RUN: llc %s --filetype=asm -o - | FileCheck %s --check-prefixes=CHECK-LLC
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target triple = "dxilv1.5-pc-shadermodel6.5-compute"
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; DXILFinalizeLinkage changes linkage of all functions that are not
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; entry points or exported function to internal.
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; CHECK: define internal void @"?f1@@YAXXZ"()
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define void @"?f1@@YAXXZ"() #0 {
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entry:
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ret void
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}
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; CHECK: define internal void @"?f2@@YAXXZ"()
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define void @"?f2@@YAXXZ"() #0 {
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entry:
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ret void
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}
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; CHECK: define internal void @"?f3@@YAXXZ"()
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define void @"?f3@@YAXXZ"() #0 {
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entry:
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ret void
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}
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; CHECK: define internal void @"?foo@@YAXXZ"()
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define void @"?foo@@YAXXZ"() #0 {
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entry:
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call void @"?f2@@YAXXZ"() #3
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ret void
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}
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; Exported function - do not change linkage
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; CHECK: define void @"?bar@@YAXXZ"()
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define void @"?bar@@YAXXZ"() #1 {
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entry:
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call void @"?f3@@YAXXZ"() #3
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ret void
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}
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; CHECK: define internal void @"?main@@YAXXZ"() #0
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define internal void @"?main@@YAXXZ"() #0 {
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entry:
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call void @"?foo@@YAXXZ"() #3
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call void @"?bar@@YAXXZ"() #3
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ret void
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}
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; Entry point function - do not change linkage
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; CHECK: define void @main() #2
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define void @main() #2 {
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entry:
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call void @"?main@@YAXXZ"()
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ret void
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}
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attributes #0 = { convergent noinline nounwind optnone}
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attributes #1 = { convergent noinline nounwind optnone "hlsl.export"}
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attributes #2 = { convergent "hlsl.numthreads"="4,1,1" "hlsl.shader"="compute"}
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attributes #3 = { convergent }
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; Make sure "hlsl.export" attribute is stripped by llc
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; CHECK-LLC-NOT: "hlsl.export"

‎llvm/test/CodeGen/DirectX/omit-bitcast-insert.ll‎

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@@ -6,7 +6,7 @@ define i64 @test(ptr %p) {
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ret i64 %v
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}
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; CHECK: define i64 @test(ptr %p) {
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; CHECK: define internal i64 @test(ptr %p) {
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; CHECK-NEXT: %v = load i64, ptr %p, align 8
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; CHECK-NEXT: ret i64 %v
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ret i64 %v
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}
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; CHECK: define i64 @test2(ptr %p) {
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; CHECK: define internal i64 @test2(ptr %p) {
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; CHECK-NEXT: store i64 0, ptr %p
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; CHECK-NEXT: %v = load i64, ptr %p, align 8
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; CHECK-NEXT: ret i64 %v
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ret i32 %3
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}
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; CHECK: define i32 @test3(ptr %0) {
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; CHECK: define internal i32 @test3(ptr %0) {
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; CHECK-NEXT: %2 = getelementptr i32, ptr %0, i32 4
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; CHECK-NEXT: %3 = load i32, ptr %2

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