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Fix SPIR-V function ordering violation in linker #145039

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Fix SPIR-V function ordering violation in linker #145039

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60 changes: 60 additions & 0 deletions llvm/lib/Linker/LinkModules.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@
#include "llvm/IR/Module.h"
#include "llvm/Linker/Linker.h"
#include "llvm/Support/Error.h"
#include "llvm/TargetParser/Triple.h"
using namespace llvm;

namespace {
Expand Down Expand Up @@ -105,6 +106,10 @@ class ModuleLinker {
const DenseSet<const Comdat *> &ReplacedDstComdats);

bool linkIfNeeded(GlobalValue &GV, SmallVectorImpl<GlobalValue *> &GVToClone);

/// Reorder functions in the module to ensure SPIR-V compliance.
/// SPIR-V requires all function declarations to appear before any function definitions.
void reorderFunctionsForSPIRV(Module &M);

public:
ModuleLinker(IRMover &Mover, std::unique_ptr<Module> SrcM, unsigned Flags,
Expand Down Expand Up @@ -615,9 +620,64 @@ bool ModuleLinker::run() {
if (InternalizeCallback)
InternalizeCallback(DstM, Internalize);

// For SPIR-V targets, ensure proper function ordering to comply with SPIR-V specification
// SPIR-V requires all function declarations to appear before any function definitions
Triple TargetTriple(DstM.getTargetTriple());
if (TargetTriple.isSPIRV()) {
reorderFunctionsForSPIRV(DstM);
}

return false;
}

void ModuleLinker::reorderFunctionsForSPIRV(Module &M) {
// Collect all function declarations and definitions
std::vector<Function*> declarations;
std::vector<Function*> definitions;

// Check if reordering is needed by detecting if any declarations appear after definitions
bool needsReordering = false;
bool seenDefinition = false;

for (Function &F : M) {
if (F.isDeclaration()) {
declarations.push_back(&F);
if (seenDefinition) {
needsReordering = true;
}
} else {
definitions.push_back(&F);
seenDefinition = true;
}
}

if (!needsReordering) return;

// Handle global arrays that reference functions (@llvm.used, @llvm.compiler.used)
// We need to update these arrays to maintain correct references after reordering
std::vector<GlobalVariable*> globalArraysToUpdate;
for (GlobalVariable &GV : M.globals())
if (GV.hasInitializer() && (GV.getName() == "llvm.used" ||
GV.getName() == "llvm.compiler.used"))
globalArraysToUpdate.push_back(&GV);

// Remove all functions from the module temporarily
std::vector<Function*> allFunctions;
for (Function &F : M)
allFunctions.push_back(&F);

// Clear the function list without destroying the functions
auto &FunctionList = M.getFunctionList();
for (Function *F : allFunctions)
F->removeFromParent();

// Re-add functions in the correct order: declarations first, then definitions
for (Function *F : declarations)
FunctionList.push_back(F);
for (Function *F : definitions)
FunctionList.push_back(F);
}

Linker::Linker(Module &M) : Mover(M) {}

bool Linker::linkInModule(
Expand Down