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Use the SSAUpdator to turn calls to eh.exception that are not in a 

landing pad into uses of registers rather than loads from a stack
slot.  Doesn't touch the 'orrible hack code - Bill needs to persuade
me harder :)

llvm-svn: 112702
This commit is contained in:
Duncan Sands 2010-09-01 14:07:47 +00:00
parent 858806fb8b
commit 4d51e3fd17
1 changed files with 86 additions and 88 deletions
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174
llvm/lib/CodeGen/DwarfEHPrepare.cpp
View File

@ -25,12 +25,12 @@
#include "llvm/Support/CallSite.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
using namespace llvm;
STATISTIC(NumLandingPadsSplit, "Number of landing pads split");
STATISTIC(NumUnwindsLowered, "Number of unwind instructions lowered");
STATISTIC(NumExceptionValuesMoved, "Number of eh.exception calls moved");
STATISTIC(NumStackTempsIntroduced, "Number of stack temporaries introduced");
namespace {
class DwarfEHPrepare : public FunctionPass {
@ -62,24 +62,11 @@ namespace {
typedef SmallPtrSet<BasicBlock*, 8> BBSet;
BBSet LandingPads;
// Stack temporary used to hold eh.exception values.
AllocaInst *ExceptionValueVar;
bool NormalizeLandingPads();
bool LowerUnwinds();
bool MoveExceptionValueCalls();
bool FinishStackTemporaries();
Instruction *CreateExceptionValueCall(BasicBlock *BB);
Instruction *CreateValueLoad(BasicBlock *BB);
/// CreateReadOfExceptionValue - Return the result of the eh.exception
/// intrinsic by calling the intrinsic if in a landing pad, or loading it
/// from the exception value variable otherwise.
Instruction *CreateReadOfExceptionValue(BasicBlock *BB) {
return LandingPads.count(BB) ?
CreateExceptionValueCall(BB) : CreateValueLoad(BB);
}
/// CleanupSelectors - Any remaining eh.selector intrinsic calls which still
/// use the "llvm.eh.catch.all.value" call need to convert to using its
@ -117,7 +104,7 @@ namespace {
virtual bool runOnFunction(Function &Fn);
// getAnalysisUsage - We need dominance frontiers for memory promotion.
// getAnalysisUsage - We need the dominator tree for handling URoR.
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<DominatorTree>();
AU.addPreserved<DominatorTree>();
@ -517,7 +504,7 @@ bool DwarfEHPrepare::LowerUnwinds() {
// Create the call...
CallInst *CI = CallInst::Create(RewindFunction,
CreateReadOfExceptionValue(TI->getParent()),
CreateExceptionValueCall(TI->getParent()),
"", TI);
CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
// ...followed by an UnreachableInst.
@ -533,9 +520,11 @@ bool DwarfEHPrepare::LowerUnwinds() {
}
/// MoveExceptionValueCalls - Ensure that eh.exception is only ever called from
/// landing pads by replacing calls outside of landing pads with loads from a
/// stack temporary. Move eh.exception calls inside landing pads to the start
/// of the landing pad (optional, but may make things simpler for later passes).
/// landing pads by replacing calls outside of landing pads with direct use of
/// a register holding the appropriate value; this requires adding calls inside
/// all landing pads to initialize the register. Also, move eh.exception calls
/// inside landing pads to the start of the landing pad (optional, but may make
/// things simpler for later passes).
bool DwarfEHPrepare::MoveExceptionValueCalls() {
// If the eh.exception intrinsic is not declared in the module then there is
// nothing to do. Speed up compilation by checking for this common case.
@ -545,49 +534,87 @@ bool DwarfEHPrepare::MoveExceptionValueCalls() {
bool Changed = false;
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;)
if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++))
if (CI->getIntrinsicID() == Intrinsic::eh_exception) {
if (!CI->use_empty()) {
Value *ExceptionValue = CreateReadOfExceptionValue(BB);
if (CI == ExceptionValue) {
// The call was at the start of a landing pad - leave it alone.
assert(LandingPads.count(BB) &&
"Created eh.exception call outside landing pad!");
continue;
}
CI->replaceAllUsesWith(ExceptionValue);
}
CI->eraseFromParent();
++NumExceptionValuesMoved;
Changed = true;
}
}
return Changed;
}
/// FinishStackTemporaries - If we introduced a stack variable to hold the
/// exception value then initialize it in each landing pad.
bool DwarfEHPrepare::FinishStackTemporaries() {
if (!ExceptionValueVar)
// Nothing to do.
return false;
bool Changed = false;
// Make sure that there is a store of the exception value at the start of
// each landing pad.
for (BBSet::iterator LI = LandingPads.begin(), LE = LandingPads.end();
// Move calls to eh.exception that are inside a landing pad to the start of
// the landing pad.
for (BBSet::const_iterator LI = LandingPads.begin(), LE = LandingPads.end();
LI != LE; ++LI) {
Instruction *ExceptionValue = CreateReadOfExceptionValue(*LI);
Instruction *Store = new StoreInst(ExceptionValue, ExceptionValueVar);
Store->insertAfter(ExceptionValue);
Changed = true;
BasicBlock *LP = *LI;
for (BasicBlock::iterator II = LP->getFirstNonPHIOrDbg(), IE = LP->end();
II != IE;)
if (EHExceptionInst *EI = dyn_cast<EHExceptionInst>(II++)) {
// Found a call to eh.exception.
if (!EI->use_empty()) {
// If there is already a call to eh.exception at the start of the
// landing pad, then get hold of it; otherwise create such a call.
Value *CallAtStart = CreateExceptionValueCall(LP);
// If the call was at the start of a landing pad then leave it alone.
if (EI == CallAtStart)
continue;
EI->replaceAllUsesWith(CallAtStart);
}
EI->eraseFromParent();
++NumExceptionValuesMoved;
Changed = true;
}
}
return Changed;
// Look for calls to eh.exception that are not in a landing pad. If one is
// found, then a register that holds the exception value will be created in
// each landing pad, and the SSAUpdater will be used to compute the values
// returned by eh.exception calls outside of landing pads.
SSAUpdater SSA;
// Remember where we found the eh.exception call, to avoid rescanning earlier
// basic blocks which we already know contain no eh.exception calls.
bool FoundCallOutsideLandingPad = false;
Function::iterator BB = F->begin();
for (Function::iterator BE = F->end(); BB != BE; ++BB) {
// Skip over landing pads.
if (LandingPads.count(BB))
continue;
for (BasicBlock::iterator II = BB->getFirstNonPHIOrDbg(), IE = BB->end();
II != IE; ++II)
if (isa<EHExceptionInst>(II)) {
SSA.Initialize(II->getType(), II->getName());
FoundCallOutsideLandingPad = true;
break;
}
if (FoundCallOutsideLandingPad)
break;
}
// If all calls to eh.exception are in landing pads then we are done.
if (!FoundCallOutsideLandingPad)
return Changed;
// Add a call to eh.exception at the start of each landing pad, and tell the
// SSAUpdater that this is the value produced by the landing pad.
for (BBSet::iterator LI = LandingPads.begin(), LE = LandingPads.end();
LI != LE; ++LI)
SSA.AddAvailableValue(*LI, CreateExceptionValueCall(*LI));
// Now turn all calls to eh.exception that are not in a landing pad into a use
// of the appropriate register.
for (Function::iterator BE = F->end(); BB != BE; ++BB) {
// Skip over landing pads.
if (LandingPads.count(BB))
continue;
for (BasicBlock::iterator II = BB->getFirstNonPHIOrDbg(), IE = BB->end();
II != IE;)
if (EHExceptionInst *EI = dyn_cast<EHExceptionInst>(II++)) {
// Found a call to eh.exception, replace it with the value from any
// upstream landing pad(s).
EI->replaceAllUsesWith(SSA.GetValueAtEndOfBlock(BB));
EI->eraseFromParent();
++NumExceptionValuesMoved;
}
}
return true;
}
/// CreateExceptionValueCall - Insert a call to the eh.exception intrinsic at
@ -610,35 +637,11 @@ Instruction *DwarfEHPrepare::CreateExceptionValueCall(BasicBlock *BB) {
return CallInst::Create(ExceptionValueIntrinsic, "eh.value.call", Start);
}
/// CreateValueLoad - Insert a load of the exception value stack variable
/// (creating it if necessary) at the start of the basic block (unless
/// there already is a load, in which case the existing load is returned).
Instruction *DwarfEHPrepare::CreateValueLoad(BasicBlock *BB) {
Instruction *Start = BB->getFirstNonPHIOrDbg();
// Is this a load of the exception temporary?
if (ExceptionValueVar)
if (LoadInst* LI = dyn_cast<LoadInst>(Start))
if (LI->getPointerOperand() == ExceptionValueVar)
// Reuse the existing load.
return Start;
// Create the temporary if we didn't already.
if (!ExceptionValueVar) {
ExceptionValueVar = new AllocaInst(PointerType::getUnqual(
Type::getInt8Ty(BB->getContext())), "eh.value", F->begin()->begin());
++NumStackTempsIntroduced;
}
// Load the value.
return new LoadInst(ExceptionValueVar, "eh.value.load", Start);
}
bool DwarfEHPrepare::runOnFunction(Function &Fn) {
bool Changed = false;
// Initialize internal state.
DT = &getAnalysis<DominatorTree>();
ExceptionValueVar = 0;
F = &Fn;
// Ensure that only unwind edges end at landing pads (a landing pad is a
@ -653,11 +656,6 @@ bool DwarfEHPrepare::runOnFunction(Function &Fn) {
// Move eh.exception calls to landing pads.
Changed |= MoveExceptionValueCalls();
// Initialize any stack temporaries we introduced.
Changed |= FinishStackTemporaries();
// TODO: Turn any stack temporaries into registers if possible.
Changed |= HandleURoRInvokes();
LandingPads.clear();