Hi,
i have the following code:
define internal %"struct.dexter::ConditionConstant"*
@_ZN6dexter18BinaryConditionAdd8evaluateEv5(%"class.dexter::BinaryConditionAdd"*)
{
entry:
%1 = getelementptr inbounds %"class.dexter::BinaryConditionAdd"* %0,
i32
0, i32 0, i32 1
%2 = load %"class.dexter::BaseCondition"** %1, align 8
%3 = bitcast %"class.dexter::BaseCondition"* %2 to
%"class.dexter::BinaryConditionAdd"*
%4 = getelementptr inbounds %"class.dexter::BinaryConditionAdd"* %3,
i32
0, i32 0, i32 0, i32 1, i32 0
%5 = bitcast %union.anon* %4 to i64*
store i64 4, i64* %5, align 8
%6 = getelementptr inbounds %"class.dexter::BinaryConditionAdd"* %3,
i32
0, i32 0, i32 0, i32 1
%7 = bitcast %"struct.dexter::ConditionConstant"* %6 to i64*
%8 = load i64* %7, align 8
%9 = add nsw i64 %8, 2
%10 = getelementptr inbounds %"class.dexter::BinaryConditionAdd"*
%0, i32
0, i32 0, i32 0, i32 1, i32 0
%11 = bitcast %union.anon* %10 to i64*
store i64 %9, i64* %11, align 8
%12 = getelementptr inbounds %"class.dexter::BinaryConditionAdd"*
%0, i32
0, i32 0, i32 0, i32 1
ret %"struct.dexter::ConditionConstant"* %12
}
%5 and %7 point to the same memory location. This is not detected because
%4 and %6 look different. But they have the same offset and the bitcast
creates. Do you have an idea how to fix that?
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I created the following pass that fixes the issue:
class bitcastCombinePass: public llvm::BasicBlockPass {
private:
JITEngine *engine;
static char ID;
public:
bitcastCombinePass(JITEngine *engine): BasicBlockPass(ID),
engine(engine) {}
virtual bool runOnBasicBlock(llvm::BasicBlock &BB) {
bool changed = false;
for(auto i = BB.begin(); i != BB.end(); i++) {
llvm::BitCastInst *bitcast
dynamic_cast<llvm::BitCastInst*>(&*i);
if(bitcast) {
// find Twin-Bitcast
for(auto i2 = BB.begin(); i2 != i; i2++) {
llvm::BitCastInst *bitcast2
dynamic_cast<llvm::BitCastInst*>(&*i2);
if(bitcast2) {
// two bitcasts ... same type?
if(bitcast->getType() == bitcast2->getType()) {
llvm::GetElementPtrInst *gep1
dynamic_cast<llvm::GetElementPtrInst*>(bitcast->getOperand(0));
llvm::GetElementPtrInst *gep2
dynamic_cast<llvm::GetElementPtrInst*>(bitcast2->getOperand(0));
// both get GEP from same operand
if(gep1 && gep2 &&
gep1->getPointerOperand() =gep2->getPointerOperand()) {
llvm::APInt offset1(sizeof(int *) * 8, 0);
llvm::APInt offset2(sizeof(int *) * 8, 0);
if(gep1->accumulateConstantOffset(*engine->executionEngine->getDataLayout(),
offset1)
&&
gep2->accumulateConstantOffset(*engine->executionEngine->getDataLayout(),
offset2)
&& offset1 == offset2) {
// bitcasts point to same value =>
replace them
bitcast->replaceAllUsesWith(bitcast2);
}
}
}
}
}
}
}
return changed;
}
};
char bitcastCombinePass::ID;
This should become part of either InstCombine or GVN I think.
2013/11/23 Carl-Philip Hänsch <cphaensch at gmail.com>
> Hi,
>
> i have the following code:
> define internal %"struct.dexter::ConditionConstant"*
>
@_ZN6dexter18BinaryConditionAdd8evaluateEv5(%"class.dexter::BinaryConditionAdd"*)
> {
> entry:
> %1 = getelementptr inbounds
%"class.dexter::BinaryConditionAdd"* %0, i32
> 0, i32 0, i32 1
> %2 = load %"class.dexter::BaseCondition"** %1, align 8
> %3 = bitcast %"class.dexter::BaseCondition"* %2 to
> %"class.dexter::BinaryConditionAdd"*
> %4 = getelementptr inbounds
%"class.dexter::BinaryConditionAdd"* %3, i32
> 0, i32 0, i32 0, i32 1, i32 0
> %5 = bitcast %union.anon* %4 to i64*
> store i64 4, i64* %5, align 8
> %6 = getelementptr inbounds
%"class.dexter::BinaryConditionAdd"* %3, i32
> 0, i32 0, i32 0, i32 1
> %7 = bitcast %"struct.dexter::ConditionConstant"* %6 to i64*
> %8 = load i64* %7, align 8
> %9 = add nsw i64 %8, 2
> %10 = getelementptr inbounds
%"class.dexter::BinaryConditionAdd"* %0,
> i32 0, i32 0, i32 0, i32 1, i32 0
> %11 = bitcast %union.anon* %10 to i64*
> store i64 %9, i64* %11, align 8
> %12 = getelementptr inbounds
%"class.dexter::BinaryConditionAdd"* %0,
> i32 0, i32 0, i32 0, i32 1
> ret %"struct.dexter::ConditionConstant"* %12
> }
>
> %5 and %7 point to the same memory location. This is not detected because
> %4 and %6 look different. But they have the same offset and the bitcast
> creates. Do you have an idea how to fix that?
>
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Carl-Philip Hänsch wrote:> Hi, > > i have the following code: > define internal %"struct.dexter::ConditionConstant"* > @_ZN6dexter18BinaryConditionAdd8evaluateEv5(%"class.dexter::BinaryConditionAdd"*) > { > entry: > %1 = getelementptr inbounds %"class.dexter::BinaryConditionAdd"* %0, > i32 0, i32 0, i32 1 > %2 = load %"class.dexter::BaseCondition"** %1, align 8 > %3 = bitcast %"class.dexter::BaseCondition"* %2 to > %"class.dexter::BinaryConditionAdd"* > %4 = getelementptr inbounds %"class.dexter::BinaryConditionAdd"* %3, > i32 0, i32 0, i32 0, i32 1, i32 0 > %5 = bitcast %union.anon* %4 to i64* > store i64 4, i64* %5, align 8 > %6 = getelementptr inbounds %"class.dexter::BinaryConditionAdd"* %3, > i32 0, i32 0, i32 0, i32 1 > %7 = bitcast %"struct.dexter::ConditionConstant"* %6 to i64* > %8 = load i64* %7, align 8 > %9 = add nsw i64 %8, 2 > %10 = getelementptr inbounds %"class.dexter::BinaryConditionAdd"* %0, > i32 0, i32 0, i32 0, i32 1, i32 0 > %11 = bitcast %union.anon* %10 to i64* > store i64 %9, i64* %11, align 8 > %12 = getelementptr inbounds %"class.dexter::BinaryConditionAdd"* %0, > i32 0, i32 0, i32 0, i32 1 > ret %"struct.dexter::ConditionConstant"* %12 > } > > %5 and %7 point to the same memory location. This is not detected > because %4 and %6 look different. But they have the same offset and the > bitcast creates. Do you have an idea how to fix that?Without seeing the definition of class.dexter::BinaryConditionAdd it's hard to tell. Is the element it's pointing to actually an i64? If it is, then we could canonicalize the gep+bitcast to just a gep. If not, then we need to have a GEP+bitcast situation, but it's possible that when we see a GEP with a single use bitcast, we could canonicalize by stripping trailing zeroes off the GEP? If instcombine did that, would GVN then be able to solve this? Nick