Introduce new ThreadLocalLowering pass

This pass will make it possible to use wasm threadlocals in genericjs, by creating and calling a function in wasm that will calculate the address in memory of the threadlocal.

Author: Maqrkk

llvm/include/llvm/Cheerp/PassRegistry.h

@@ -41,6 +41,7 @@
 #include "llvm/Cheerp/CallConstructors.h"
 #include "llvm/Cheerp/CommandLine.h"
 #include "llvm/Cheerp/CheerpLowerAtomic.h"
+#include "llvm/Cheerp/ThreadLocalLowering.h"
 
 namespace cheerp {
 

llvm/include/llvm/Cheerp/ThreadLocalLowering.h

@@ -0,0 +1,40 @@
+//===-- ThreadLocalLowering.h - Cheerp helper -------------------------===//
+//
+//                     Cheerp: The C++ compiler for the Web
+//
+// This file is distributed under the Apache License v2.0 with LLVM Exceptions.
+// See LICENSE.TXT for details.
+//
+// Copyright 2024-2025 Leaning Technologies
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef CHEERP_THREAD_LOCAL_LOWERING_H
+#define CHEERP_THREAD_LOCAL_LOWERING_H
+
+#include "llvm/IR/PassManager.h"
+#include "llvm/Cheerp/GlobalDepsAnalyzer.h"
+
+namespace cheerp{
+
+using namespace llvm;
+
+class ThreadLocalLoweringInnerPass: public PassInfoMixin<ThreadLocalLoweringInnerPass> {
+	GlobalDepsAnalyzer& GDA;
+public:
+	ThreadLocalLoweringInnerPass(GlobalDepsAnalyzer& GDA) : GDA(GDA)
+	{
+	}
+	PreservedAnalyses run(Function& F, FunctionAnalysisManager& FAM);
+	static bool isRequired() { return true;}
+};
+
+class ThreadLocalLoweringPass: public PassInfoMixin<ThreadLocalLoweringPass> {
+public:
+	PreservedAnalyses run(Module& M, ModuleAnalysisManager& MAM);
+	static bool isRequired() { return true;}
+};
+
+}
+
+#endif

llvm/lib/CheerpUtils/CMakeLists.txt

@@ -35,6 +35,7 @@ add_llvm_component_library(LLVMCheerpUtils
   FinalizeMemoryInfo.cpp
   CheerpLowerAtomic.cpp
   JsExport.cpp
+  ThreadLocalLowering.cpp
   )
 
 add_dependencies(LLVMCheerpUtils intrinsics_gen)

llvm/lib/CheerpUtils/PointerAnalyzer.cpp

@@ -672,6 +672,7 @@ PointerKindWrapper& PointerUsageVisitor::visitValue(PointerKindWrapper& ret, con
 		case Intrinsic::invariant_start:
 			return CacheAndReturn(visitValue(ret, intrinsic->getArgOperand(1), /*first*/ false));
 		case Intrinsic::stacksave:
+		case Intrinsic::threadlocal_address:
 			return CacheAndReturn(ret = PointerKindWrapper(RAW));
 		case Intrinsic::invariant_end:
 		case Intrinsic::vastart:

llvm/lib/CheerpUtils/ThreadLocalLowering.cpp

@@ -0,0 +1,127 @@
+//===-- ThreadLocalLowering.cpp - Cheerp helper -------------------------===//
+//
+//                     Cheerp: The C++ compiler for the Web
+//
+// This file is distributed under the Apache License v2.0 with LLVM Exceptions.
+// See LICENSE.TXT for details.
+//
+// Copyright 2024-2025 Leaning Technologies
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Cheerp/ThreadLocalLowering.h"
+#include "llvm/Cheerp/GlobalDepsAnalyzer.h"
+#include "llvm/Cheerp/LinearMemoryHelper.h"
+#include "llvm/Cheerp/InvokeWrapping.h"
+#include "llvm/Cheerp/Registerize.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/IRBuilder.h"
+
+using namespace llvm;
+
+namespace cheerp
+{
+
+static Function* getOrCreateThreadLocalWrapper(Module* M, GlobalDepsAnalyzer& GDA)
+{
+	Type* i8Ty = IntegerType::getInt8Ty(M->getContext());
+	Type* i8PtrTy = PointerType::get(i8Ty, 0);
+	Type* i32Ty = IntegerType::getInt32Ty(M->getContext());
+	Type* argTy[] = {i32Ty};
+	FunctionType* fTy = FunctionType::get(i8PtrTy,ArrayRef<Type*>(argTy, 1), false);
+	Function* wrapper = cast<Function>(M->getOrInsertFunction("__getThreadLocalAddress", fTy).getCallee());
+	if (!wrapper->empty())
+		return wrapper;
+
+	BasicBlock* entry = BasicBlock::Create(M->getContext(),"entry", wrapper);
+	IRBuilder<> Builder(entry);
+	// Get the thread local address.
+	Function* threadPointerIntrinsic = Intrinsic::getDeclaration(M, Intrinsic::cheerp_get_thread_pointer);
+	Value* threadPointer = Builder.CreateCall(threadPointerIntrinsic);
+	// Add the offset argument
+	Value* offset = wrapper->getArg(0);
+	Value* address = Builder.CreateAdd(threadPointer, offset);
+	// Bitcast to a pointer
+	address = Builder.CreateIntToPtr(address, i8PtrTy);
+	Builder.CreateRet(address);
+
+	wrapper->setSection("asmjs");
+	GDA.insertAsmJSExport(wrapper);
+	return wrapper;
+}
+
+bool replaceThreadLocalIntrinsicWithFunction(Function& F, GlobalDepsAnalyzer& GDA)
+{
+	Module* M = F.getParent();
+	bool changed = false;
+	SmallVector<Instruction*, 8> deleteList;
+
+	for (BasicBlock& BB: F)
+	{
+		for (Instruction& I: BB)
+		{
+			if (isa<IntrinsicInst>(I))
+			{
+				IntrinsicInst& II = cast<IntrinsicInst>(I);
+				Intrinsic::ID intrId = II.getIntrinsicID();
+				if (intrId == Intrinsic::threadlocal_address)
+				{
+					IRBuilder<> Builder(&II);
+					// Replace call to intrinsic with function
+					// 1. Use an intrinsic that will be the offset for the threadlocal.
+					Type* argTy[] = {II.getOperand(0)->getType()};
+					Function* offsetIntrinsic = Intrinsic::getDeclaration(M, Intrinsic::cheerp_get_threadlocal_offset, argTy);
+					Value* offset = Builder.CreateCall(offsetIntrinsic, II.getOperand(0));
+					// 2. Pass this offset to the wasm function that will calculate the address from the thread pointer.
+					Function* newFunc = getOrCreateThreadLocalWrapper(M, GDA);
+					Value* newCall = Builder.CreateCall(newFunc, offset);
+					// 3. Bitcast return code from this function to required type.
+					Type* origType = II.getType();
+					if (origType != newCall->getType())
+						newCall = Builder.CreateBitCast(newCall, origType);
+					I.replaceAllUsesWith(newCall);
+					deleteList.push_back(&I);
+					changed = true;
+				}
+			}
+		}
+	}
+	for (Instruction* I: deleteList)
+		I->eraseFromParent();
+	return changed;
+}
+
+PreservedAnalyses ThreadLocalLoweringInnerPass::run(Function& F, FunctionAnalysisManager& FAM)
+{
+	if (F.getSection() == "asmjs")
+		return PreservedAnalyses::all();
+
+	// Find calls to threadlocal.address intrinsic, replace with calls to function.
+	bool changed = replaceThreadLocalIntrinsicWithFunction(F, GDA);
+	if (!changed)
+		return PreservedAnalyses::all();
+	PreservedAnalyses PA;
+	PA.preserve<PointerAnalysis>();
+	PA.preserve<RegisterizeAnalysis>();
+	PA.preserve<GlobalDepsAnalysis>();
+	PA.preserve<DominatorTreeAnalysis>();
+	PA.preserve<InvokeWrappingAnalysis>();
+	return PA;
+}
+
+PreservedAnalyses ThreadLocalLoweringPass::run(Module& M, ModuleAnalysisManager& MAM)
+{
+	FunctionPassManager FPM;
+
+	GlobalDepsAnalyzer& GDA = MAM.getResult<GlobalDepsAnalysis>(M);
+	FPM.addPass(ThreadLocalLoweringInnerPass(GDA));
+
+	ModulePassManager MPM;
+
+	MPM.addPass(createModuleToFunctionPassAdaptor(std::move(FPM)));
+	PreservedAnalyses PA = MPM.run(M, MAM);
+	return PA;
+}
+
+}

llvm/lib/Target/WebAssembly/CheerpWritePass.cpp

@@ -241,6 +241,7 @@ bool CheerpWritePass::runOnModule(Module& M)
   MPM.addPass(cheerp::InvokeWrappingPass());
   if (isWasmTarget)
     MPM.addPass(cheerp::AllocaLoweringPass());
+  MPM.addPass(cheerp::ThreadLocalLoweringPass());
   MPM.addPass(cheerp::FFIWrappingPass());
   MPM.addPass(createModuleToFunctionPassAdaptor(cheerp::FixIrreducibleControlFlowPass()));
   MPM.addPass(createModuleToFunctionPassAdaptor(cheerp::PointerArithmeticToArrayIndexingPass()));