MergeFunctions: Preserve debug info in thunks, under option -mergefunc-preserve-debug-info
Summary:
Under option -mergefunc-preserve-debug-info we:
- Do not create a new function for a thunk.
- Retain the debug info for a thunk's parameters (and associated
instructions for the debug info) from the entry block.
Note: -debug will display the algorithm at work.
- Create debug-info for the call (to the shared implementation) made by
a thunk and its return value.
- Erase the rest of the function, retaining the (minimally sized) entry
block to create a thunk.
- Preserve a thunk's call site to point to the thunk even when both occur
within the same translation unit, to aid debugability. Note that this
behaviour differs from the underlying -mergefunc implementation which
modifies the thunk's call site to point to the shared implementation
when both occur within the same translation unit.
Reviewers: echristo, eeckstein, dblaikie, aprantl, friss
Reviewed By: aprantl
Subscribers: davide, fhahn, jfb, mehdi_amini, llvm-commits
Differential Revision: https://reviews.llvm.org/D28075
llvm-svn: 292702
diff --git a/llvm/lib/Transforms/IPO/MergeFunctions.cpp b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
index e0bb0eb..43c8ce3 100644
--- a/llvm/lib/Transforms/IPO/MergeFunctions.cpp
+++ b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
@@ -96,8 +96,10 @@
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/ValueHandle.h"
@@ -127,6 +129,26 @@
"'0' disables this check. Works only with '-debug' key."),
cl::init(0), cl::Hidden);
+// Under option -mergefunc-preserve-debug-info we:
+// - Do not create a new function for a thunk.
+// - Retain the debug info for a thunk's parameters (and associated
+// instructions for the debug info) from the entry block.
+// Note: -debug will display the algorithm at work.
+// - Create debug-info for the call (to the shared implementation) made by
+// a thunk and its return value.
+// - Erase the rest of the function, retaining the (minimally sized) entry
+// block to create a thunk.
+// - Preserve a thunk's call site to point to the thunk even when both occur
+// within the same translation unit, to aid debugability. Note that this
+// behaviour differs from the underlying -mergefunc implementation which
+// modifies the thunk's call site to point to the shared implementation
+// when both occur within the same translation unit.
+static cl::opt<bool>
+ MergeFunctionsPDI("mergefunc-preserve-debug-info", cl::Hidden,
+ cl::init(false),
+ cl::desc("Preserve debug info in thunk when mergefunc "
+ "transformations are made."));
+
namespace {
class FunctionNode {
@@ -215,8 +237,21 @@
/// Replace G with a thunk or an alias to F. Deletes G.
void writeThunkOrAlias(Function *F, Function *G);
- /// Replace G with a simple tail call to bitcast(F). Also replace direct uses
- /// of G with bitcast(F). Deletes G.
+ /// Fill PDIUnrelatedWL with instructions from the entry block that are
+ /// unrelated to parameter related debug info.
+ void filterInstsUnrelatedToPDI(BasicBlock *GEntryBlock,
+ std::vector<Instruction *> &PDIUnrelatedWL);
+
+ /// Erase the rest of the CFG (i.e. barring the entry block).
+ void eraseTail(Function *G);
+
+ /// Erase the instructions in PDIUnrelatedWL as they are unrelated to the
+ /// parameter debug info, from the entry block.
+ void eraseInstsUnrelatedToPDI(std::vector<Instruction *> &PDIUnrelatedWL);
+
+ /// Replace G with a simple tail call to bitcast(F). Also (unless
+ /// MergeFunctionsPDI holds) replace direct uses of G with bitcast(F),
+ /// delete G.
void writeThunk(Function *F, Function *G);
/// Replace G with an alias to F. Deletes G.
@@ -461,51 +496,242 @@
return Builder.CreateBitCast(V, DestTy);
}
-// Replace G with a simple tail call to bitcast(F). Also replace direct uses
-// of G with bitcast(F). Deletes G.
+// Erase the instructions in PDIUnrelatedWL as they are unrelated to the
+// parameter debug info, from the entry block.
+void MergeFunctions::eraseInstsUnrelatedToPDI(
+ std::vector<Instruction *> &PDIUnrelatedWL) {
+
+ DEBUG(dbgs() << " Erasing instructions (in reverse order of appearance in "
+ "entry block) unrelated to parameter debug info from entry "
+ "block: {\n");
+ while (!PDIUnrelatedWL.empty()) {
+ Instruction *I = PDIUnrelatedWL.back();
+ DEBUG(dbgs() << " Deleting Instruction: ");
+ DEBUG(I->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ I->eraseFromParent();
+ PDIUnrelatedWL.pop_back();
+ }
+ DEBUG(dbgs() << " } // Done erasing instructions unrelated to parameter "
+ "debug info from entry block. \n");
+}
+
+// Reduce G to its entry block.
+void MergeFunctions::eraseTail(Function *G) {
+
+ std::vector<BasicBlock *> WorklistBB;
+ for (Function::iterator BBI = std::next(G->begin()), BBE = G->end();
+ BBI != BBE; ++BBI) {
+ BBI->dropAllReferences();
+ WorklistBB.push_back(&*BBI);
+ }
+ while (!WorklistBB.empty()) {
+ BasicBlock *BB = WorklistBB.back();
+ BB->eraseFromParent();
+ WorklistBB.pop_back();
+ }
+}
+
+// We are interested in the following instructions from the entry block as being
+// related to parameter debug info:
+// - @llvm.dbg.declare
+// - stores from the incoming parameters to locations on the stack-frame
+// - allocas that create these locations on the stack-frame
+// - @llvm.dbg.value
+// - the entry block's terminator
+// The rest are unrelated to debug info for the parameters; fill up
+// PDIUnrelatedWL with such instructions.
+void MergeFunctions::filterInstsUnrelatedToPDI(
+ BasicBlock *GEntryBlock, std::vector<Instruction *> &PDIUnrelatedWL) {
+
+ std::set<Instruction *> PDIRelated;
+ for (BasicBlock::iterator BI = GEntryBlock->begin(), BIE = GEntryBlock->end();
+ BI != BIE; ++BI) {
+ if (auto *DVI = dyn_cast<DbgValueInst>(&*BI)) {
+ DEBUG(dbgs() << " Deciding: ");
+ DEBUG(BI->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ DILocalVariable *DILocVar = DVI->getVariable();
+ if (DILocVar->isParameter()) {
+ DEBUG(dbgs() << " Include (parameter): ");
+ DEBUG(BI->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ PDIRelated.insert(&*BI);
+ } else {
+ DEBUG(dbgs() << " Delete (!parameter): ");
+ DEBUG(BI->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ }
+ } else if (auto *DDI = dyn_cast<DbgDeclareInst>(&*BI)) {
+ DEBUG(dbgs() << " Deciding: ");
+ DEBUG(BI->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ DILocalVariable *DILocVar = DDI->getVariable();
+ if (DILocVar->isParameter()) {
+ DEBUG(dbgs() << " Parameter: ");
+ DEBUG(DILocVar->print(dbgs()));
+ AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress());
+ if (AI) {
+ DEBUG(dbgs() << " Processing alloca users: ");
+ DEBUG(dbgs() << "\n");
+ for (User *U : AI->users()) {
+ if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
+ if (Value *Arg = SI->getValueOperand()) {
+ if (dyn_cast<Argument>(Arg)) {
+ DEBUG(dbgs() << " Include: ");
+ DEBUG(AI->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ PDIRelated.insert(AI);
+ DEBUG(dbgs() << " Include (parameter): ");
+ DEBUG(SI->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ PDIRelated.insert(SI);
+ DEBUG(dbgs() << " Include: ");
+ DEBUG(BI->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ PDIRelated.insert(&*BI);
+ } else {
+ DEBUG(dbgs() << " Delete (!parameter): ");
+ DEBUG(SI->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ }
+ }
+ } else {
+ DEBUG(dbgs() << " Defer: ");
+ DEBUG(U->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ }
+ }
+ } else {
+ DEBUG(dbgs() << " Delete (alloca NULL): ");
+ DEBUG(BI->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ }
+ } else {
+ DEBUG(dbgs() << " Delete (!parameter): ");
+ DEBUG(BI->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ }
+ } else if (dyn_cast<TerminatorInst>(BI) == GEntryBlock->getTerminator()) {
+ DEBUG(dbgs() << " Will Include Terminator: ");
+ DEBUG(BI->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ PDIRelated.insert(&*BI);
+ } else {
+ DEBUG(dbgs() << " Defer: ");
+ DEBUG(BI->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ }
+ }
+ DEBUG(dbgs()
+ << " Report parameter debug info related/related instructions: {\n");
+ for (BasicBlock::iterator BI = GEntryBlock->begin(), BE = GEntryBlock->end();
+ BI != BE; ++BI) {
+
+ Instruction *I = &*BI;
+ if (PDIRelated.find(I) == PDIRelated.end()) {
+ DEBUG(dbgs() << " !PDIRelated: ");
+ DEBUG(I->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ PDIUnrelatedWL.push_back(I);
+ } else {
+ DEBUG(dbgs() << " PDIRelated: ");
+ DEBUG(I->print(dbgs()));
+ DEBUG(dbgs() << "\n");
+ }
+ }
+ DEBUG(dbgs() << " }\n");
+}
+
+// Replace G with a simple tail call to bitcast(F). Also (unless
+// MergeFunctionsPDI holds) replace direct uses of G with bitcast(F),
+// delete G. Under MergeFunctionsPDI, we use G itself for creating
+// the thunk as we preserve the debug info (and associated instructions)
+// from G's entry block pertaining to G's incoming arguments which are
+// passed on as corresponding arguments in the call that G makes to F.
+// For better debugability, under MergeFunctionsPDI, we do not modify G's
+// call sites to point to F even when within the same translation unit.
void MergeFunctions::writeThunk(Function *F, Function *G) {
- if (!G->isInterposable()) {
- // Redirect direct callers of G to F.
+ if (!G->isInterposable() && !MergeFunctionsPDI) {
+ // Redirect direct callers of G to F. (See note on MergeFunctionsPDI
+ // above).
replaceDirectCallers(G, F);
}
// If G was internal then we may have replaced all uses of G with F. If so,
- // stop here and delete G. There's no need for a thunk.
- if (G->hasLocalLinkage() && G->use_empty()) {
+ // stop here and delete G. There's no need for a thunk. (See note on
+ // MergeFunctionsPDI above).
+ if (G->hasLocalLinkage() && G->use_empty() && !MergeFunctionsPDI) {
G->eraseFromParent();
return;
}
- Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "",
- G->getParent());
- BasicBlock *BB = BasicBlock::Create(F->getContext(), "", NewG);
- IRBuilder<> Builder(BB);
+ BasicBlock *GEntryBlock = nullptr;
+ std::vector<Instruction *> PDIUnrelatedWL;
+ BasicBlock *BB = nullptr;
+ Function *NewG = nullptr;
+ if (MergeFunctionsPDI) {
+ DEBUG(dbgs() << "writeThunk: (MergeFunctionsPDI) Do not create a new "
+ "function as thunk; retain original: "
+ << G->getName() << "()\n");
+ GEntryBlock = &G->getEntryBlock();
+ DEBUG(dbgs() << "writeThunk: (MergeFunctionsPDI) filter parameter related "
+ "debug info for "
+ << G->getName() << "() {\n");
+ filterInstsUnrelatedToPDI(GEntryBlock, PDIUnrelatedWL);
+ GEntryBlock->getTerminator()->eraseFromParent();
+ BB = GEntryBlock;
+ } else {
+ NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "",
+ G->getParent());
+ BB = BasicBlock::Create(F->getContext(), "", NewG);
+ }
+ IRBuilder<> Builder(BB);
+ Function *H = MergeFunctionsPDI ? G : NewG;
SmallVector<Value *, 16> Args;
unsigned i = 0;
FunctionType *FFTy = F->getFunctionType();
- for (Argument & AI : NewG->args()) {
+ for (Argument & AI : H->args()) {
Args.push_back(createCast(Builder, &AI, FFTy->getParamType(i)));
++i;
}
CallInst *CI = Builder.CreateCall(F, Args);
+ ReturnInst *RI = nullptr;
CI->setTailCall();
CI->setCallingConv(F->getCallingConv());
CI->setAttributes(F->getAttributes());
- if (NewG->getReturnType()->isVoidTy()) {
- Builder.CreateRetVoid();
+ if (H->getReturnType()->isVoidTy()) {
+ RI = Builder.CreateRetVoid();
} else {
- Builder.CreateRet(createCast(Builder, CI, NewG->getReturnType()));
+ RI = Builder.CreateRet(createCast(Builder, CI, H->getReturnType()));
}
- NewG->copyAttributesFrom(G);
- NewG->takeName(G);
- removeUsers(G);
- G->replaceAllUsesWith(NewG);
- G->eraseFromParent();
+ if (MergeFunctionsPDI) {
+ DISubprogram *DIS = G->getSubprogram();
+ if (DIS) {
+ DebugLoc CIDbgLoc = DebugLoc::get(DIS->getScopeLine(), 0, DIS);
+ DebugLoc RIDbgLoc = DebugLoc::get(DIS->getScopeLine(), 0, DIS);
+ CI->setDebugLoc(CIDbgLoc);
+ RI->setDebugLoc(RIDbgLoc);
+ } else {
+ DEBUG(dbgs() << "writeThunk: (MergeFunctionsPDI) No DISubprogram for "
+ << G->getName() << "()\n");
+ }
+ eraseTail(G);
+ eraseInstsUnrelatedToPDI(PDIUnrelatedWL);
+ DEBUG(dbgs() << "} // End of parameter related debug info filtering for: "
+ << G->getName() << "()\n");
+ } else {
+ NewG->copyAttributesFrom(G);
+ NewG->takeName(G);
+ removeUsers(G);
+ G->replaceAllUsesWith(NewG);
+ G->eraseFromParent();
+ }
- DEBUG(dbgs() << "writeThunk: " << NewG->getName() << '\n');
+ DEBUG(dbgs() << "writeThunk: " << H->getName() << '\n');
++NumThunksWritten;
}