Add an implementation of thunks for varargs methods. The implementation is a bit messy, but it is correct as long as the method in question doesn't use indirect gotos. A couple of possible alternative implementations are outlined in FIXME's in this patch. rdar://problem/8077308 .
llvm-svn: 130993
diff --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
index 581467c..c7ef9c7 100644
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -21,6 +21,7 @@
#include "llvm/ADT/SetVector.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Format.h"
+#include "llvm/Transforms/Utils/Cloning.h"
#include <algorithm>
#include <cstdio>
@@ -2636,6 +2637,131 @@
}
#endif
+static RValue PerformReturnAdjustment(CodeGenFunction &CGF,
+ QualType ResultType, RValue RV,
+ const ThunkInfo &Thunk) {
+ // Emit the return adjustment.
+ bool NullCheckValue = !ResultType->isReferenceType();
+
+ llvm::BasicBlock *AdjustNull = 0;
+ llvm::BasicBlock *AdjustNotNull = 0;
+ llvm::BasicBlock *AdjustEnd = 0;
+
+ llvm::Value *ReturnValue = RV.getScalarVal();
+
+ if (NullCheckValue) {
+ AdjustNull = CGF.createBasicBlock("adjust.null");
+ AdjustNotNull = CGF.createBasicBlock("adjust.notnull");
+ AdjustEnd = CGF.createBasicBlock("adjust.end");
+
+ llvm::Value *IsNull = CGF.Builder.CreateIsNull(ReturnValue);
+ CGF.Builder.CreateCondBr(IsNull, AdjustNull, AdjustNotNull);
+ CGF.EmitBlock(AdjustNotNull);
+ }
+
+ ReturnValue = PerformTypeAdjustment(CGF, ReturnValue,
+ Thunk.Return.NonVirtual,
+ Thunk.Return.VBaseOffsetOffset);
+
+ if (NullCheckValue) {
+ CGF.Builder.CreateBr(AdjustEnd);
+ CGF.EmitBlock(AdjustNull);
+ CGF.Builder.CreateBr(AdjustEnd);
+ CGF.EmitBlock(AdjustEnd);
+
+ llvm::PHINode *PHI = CGF.Builder.CreatePHI(ReturnValue->getType(), 2);
+ PHI->addIncoming(ReturnValue, AdjustNotNull);
+ PHI->addIncoming(llvm::Constant::getNullValue(ReturnValue->getType()),
+ AdjustNull);
+ ReturnValue = PHI;
+ }
+
+ return RValue::get(ReturnValue);
+}
+
+// This function does roughly the same thing as GenerateThunk, but in a
+// very different way, so that va_start and va_end work correctly.
+// FIXME: This function assumes "this" is the first non-sret LLVM argument of
+// a function, and that there is an alloca built in the entry block
+// for all accesses to "this".
+// FIXME: This function assumes there is only one "ret" statement per function.
+// FIXME: Cloning isn't correct in the presence of indirect goto!
+// FIXME: This implementation of thunks bloats codesize by duplicating the
+// function definition. There are alternatives:
+// 1. Add some sort of stub support to LLVM for cases where we can
+// do a this adjustment, then a sibcall.
+// 2. We could transform the definition to take a va_list instead of an
+// actual variable argument list, then have the thunks (including a
+// no-op thunk for the regular definition) call va_start/va_end.
+// There's a bit of per-call overhead for this solution, but it's
+// better for codesize if the definition is long.
+void CodeGenFunction::GenerateVarArgsThunk(
+ llvm::Function *Fn,
+ const CGFunctionInfo &FnInfo,
+ GlobalDecl GD, const ThunkInfo &Thunk) {
+ const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
+ const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>();
+ QualType ResultType = FPT->getResultType();
+
+ // Get the original function
+ const llvm::Type *Ty =
+ CGM.getTypes().GetFunctionType(FnInfo, /*IsVariadic*/true);
+ llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
+ llvm::Function *BaseFn = cast<llvm::Function>(Callee);
+
+ // Clone to thunk.
+ llvm::Function *NewFn = llvm::CloneFunction(BaseFn);
+ CGM.getModule().getFunctionList().push_back(NewFn);
+ Fn->replaceAllUsesWith(NewFn);
+ NewFn->takeName(Fn);
+ Fn->eraseFromParent();
+ Fn = NewFn;
+
+ // "Initialize" CGF (minimally).
+ CurFn = Fn;
+
+ // Get the "this" value
+ llvm::Function::arg_iterator AI = Fn->arg_begin();
+ if (CGM.ReturnTypeUsesSRet(FnInfo))
+ ++AI;
+
+ // Find the first store of "this", which will be to the alloca associated
+ // with "this".
+ llvm::Value *ThisPtr = &*AI;
+ llvm::BasicBlock *EntryBB = Fn->begin();
+ llvm::Instruction *ThisStore = 0;
+ for (llvm::BasicBlock::iterator I = EntryBB->begin(), E = EntryBB->end();
+ I != E; I++) {
+ if (isa<llvm::StoreInst>(I) && I->getOperand(0) == ThisPtr) {
+ ThisStore = cast<llvm::StoreInst>(I);
+ break;
+ }
+ }
+ assert(ThisStore && "Store of this should be in entry block?");
+ // Adjust "this", if necessary.
+ Builder.SetInsertPoint(ThisStore);
+ llvm::Value *AdjustedThisPtr =
+ PerformTypeAdjustment(*this, ThisPtr,
+ Thunk.This.NonVirtual,
+ Thunk.This.VCallOffsetOffset);
+ ThisStore->setOperand(0, AdjustedThisPtr);
+
+ if (!Thunk.Return.isEmpty()) {
+ // Fix up the returned value, if necessary.
+ for (llvm::Function::iterator I = Fn->begin(), E = Fn->end(); I != E; I++) {
+ llvm::Instruction *T = I->getTerminator();
+ if (isa<llvm::ReturnInst>(T)) {
+ RValue RV = RValue::get(T->getOperand(0));
+ T->eraseFromParent();
+ Builder.SetInsertPoint(&*I);
+ RV = PerformReturnAdjustment(*this, ResultType, RV, Thunk);
+ Builder.CreateRet(RV.getScalarVal());
+ break;
+ }
+ }
+ }
+}
+
void CodeGenFunction::GenerateThunk(llvm::Function *Fn,
const CGFunctionInfo &FnInfo,
GlobalDecl GD, const ThunkInfo &Thunk) {
@@ -2715,45 +2841,8 @@
// Now emit our call.
RValue RV = EmitCall(FnInfo, Callee, Slot, CallArgs, MD);
- if (!Thunk.Return.isEmpty()) {
- // Emit the return adjustment.
- bool NullCheckValue = !ResultType->isReferenceType();
-
- llvm::BasicBlock *AdjustNull = 0;
- llvm::BasicBlock *AdjustNotNull = 0;
- llvm::BasicBlock *AdjustEnd = 0;
-
- llvm::Value *ReturnValue = RV.getScalarVal();
-
- if (NullCheckValue) {
- AdjustNull = createBasicBlock("adjust.null");
- AdjustNotNull = createBasicBlock("adjust.notnull");
- AdjustEnd = createBasicBlock("adjust.end");
-
- llvm::Value *IsNull = Builder.CreateIsNull(ReturnValue);
- Builder.CreateCondBr(IsNull, AdjustNull, AdjustNotNull);
- EmitBlock(AdjustNotNull);
- }
-
- ReturnValue = PerformTypeAdjustment(*this, ReturnValue,
- Thunk.Return.NonVirtual,
- Thunk.Return.VBaseOffsetOffset);
-
- if (NullCheckValue) {
- Builder.CreateBr(AdjustEnd);
- EmitBlock(AdjustNull);
- Builder.CreateBr(AdjustEnd);
- EmitBlock(AdjustEnd);
-
- llvm::PHINode *PHI = Builder.CreatePHI(ReturnValue->getType(), 2);
- PHI->addIncoming(ReturnValue, AdjustNotNull);
- PHI->addIncoming(llvm::Constant::getNullValue(ReturnValue->getType()),
- AdjustNull);
- ReturnValue = PHI;
- }
-
- RV = RValue::get(ReturnValue);
- }
+ if (!Thunk.Return.isEmpty())
+ RV = PerformReturnAdjustment(*this, ResultType, RV, Thunk);
if (!ResultType->isVoidType() && Slot.isNull())
CGM.getCXXABI().EmitReturnFromThunk(*this, RV, ResultType);
@@ -2823,8 +2912,18 @@
return;
}
- // Actually generate the thunk body.
- CodeGenFunction(CGM).GenerateThunk(ThunkFn, FnInfo, GD, Thunk);
+ if (ThunkFn->isVarArg()) {
+ // Varargs thunks are special; we can't just generate a call because
+ // we can't copy the varargs. Our implementation is rather
+ // expensive/sucky at the moment, so don't generate the thunk unless
+ // we have to.
+ // FIXME: Do something better here; GenerateVarArgsThunk is extremely ugly.
+ if (!UseAvailableExternallyLinkage)
+ CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, Thunk);
+ } else {
+ // Normal thunk body generation.
+ CodeGenFunction(CGM).GenerateThunk(ThunkFn, FnInfo, GD, Thunk);
+ }
if (UseAvailableExternallyLinkage)
ThunkFn->setLinkage(llvm::GlobalValue::AvailableExternallyLinkage);