[llvm-dev] Bug in replaceUsesOfWith: does not keep addrspace consistent in GEP

[Quentin Colombet via llvm-dev]

> On Oct 13, 2017, at 5:33 PM, Siddharth Bhat <siddu.druid at gmail.com> wrote:
> 
> I see. So, compatibility of two values depends on address spaces as well? I didn't know that, thank you.
> 
> In that case, is there some uniform way to say "give me a new instruction with this (possibly incompatible) value"? 
> 
> 
Usually you have to add casts if the value types don’t match.
Look in InstCombine and such for examples.

> For context, I'm taking some code that was generated in a different address space context, and I'm copying it to a different context (with a different address space).
> 

You’ll need a addrspace cast to do that.

> Thanks,
> Siddharth.
> 
> 
> On Sat 14 Oct, 2017, 02:30 Quentin Colombet, <qcolombet at apple.com <mailto:qcolombet at apple.com>> wrote:
> Hi Siddharth,
> 
> I haven’t read through your code or example, so my reply may be off but I would say this is expected.
> When you call replaceUsesOfWith, you have to make sure the values are “compatible” before doing this.
> If the address space of both values are different and that’s not okay, then you will create wrong code.
> 
> Cheers,
> -Quentin
> 
> 
>> On Oct 13, 2017, at 5:17 PM, Siddharth Bhat via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>> 
> 
>> Hello,
>> 
>> Calling `replaceUsesOfWith` with a value in a different addrspace does not keep the addrspace of a GEP consistent. Is this known? Is this a bug or expected behaviour?
>> 
>> Minimal counterexample link <https://gist.github.com/bollu/152ba5e1c20c03c7fc6d8c7b23ba828f>
>> 
>> Reproduced here:
>> 
>> #include <iostream>
>> #include "llvm/ADT/APFloat.h"
>> #include "llvm/ADT/STLExtras.h"
>> #include "llvm/ADT/SmallVector.h"
>> #include "llvm/Bitcode/BitcodeWriter.h"
>> #include "llvm/IR/BasicBlock.h"
>> #include "llvm/IR/Constants.h"
>> #include "llvm/IR/DerivedTypes.h"
>> #include "llvm/IR/Function.h"
>> #include "llvm/IR/IRBuilder.h"
>> #include "llvm/IR/Instructions.h"
>> #include "llvm/IR/LLVMContext.h"
>> #include "llvm/IR/Module.h"
>> #include "llvm/IR/Type.h"
>> #include "llvm/IR/Verifier.h"
>> #include "llvm/Support/FileSystem.h"
>> using namespace llvm;
>> using namespace std;
>> 
>> static const bool NON_VAR_ARG = false;
>> 
>> static AssertingVH<Function> getOrCreateFunction(Module &m, FunctionType *FTy,
>>                                                  std::string name) {
>>     Function *F = m.getFunction(name);
>>     if (F) return F;
>> 
>>     return Function::Create(FTy, GlobalValue::ExternalLinkage, name, &m);
>> };
>> static const bool SHOW_ERROR = false;
>> 
>> int main() {
>>     static LLVMContext ctx;
>>     static IRBuilder<> Builder(ctx);
>> 
>>     Module *m = new Module("Module", ctx);
>>     Function *F = getOrCreateFunction(
>>         *m,
>>         FunctionType::get(Builder.getInt64Ty(),
>>                           {PointerType::get(Builder.getInt32Ty(), 42),
>>                           PointerType::get(Builder.getInt32Ty(), 1)},
>>                           NON_VAR_ARG),
>>         "f");
>>     auto It = F->arg_begin();
>>     Value *Arg = &*It;
>>     It++;
>>     Value *Arg2 = &*It;
>> 
>>     BasicBlock *Entry = BasicBlock::Create(ctx, "entry", F);
>>     Builder.SetInsertPoint(Entry);
>> 
>>     Instruction *Slot = nullptr;
>>     if (SHOW_ERROR) {
>>         Slot = cast<Instruction>(Builder.CreateGEP(Arg, {Builder.getInt64(1)}, "slot"));
>>         errs() << "Slot(original): " << *Slot << "\n";
>>         Slot->replaceUsesOfWith(Arg, Arg2);
>>         errs() << "Slot(replaced): " << *Slot << "\n";
>>     }
>>     else {
>>         Slot = cast<Instruction>(Builder.CreateGEP(Arg2, {Builder.getInt64(1)}, "slot"));
>>     }
>>     Value *TypedSlot = Builder.CreateBitCast(Slot, PointerType::get(Builder.getInt64Ty(), 1), "slot_typed");
>>     Value *Load = Builder.CreateLoad(TypedSlot, "Val");
>>     Builder.CreateRet(Load);
>> 
>>     if (verifyModule(*m) == 1) {
>>         errs() << "module has an error: ";
>>         verifyModule(*m, &errs());
>>         report_fatal_error("buggy module.");
>>     }
>>     outs() << *m << "\n";
>>     // llvm::WriteBitcodeToFile(m, outs());
>> 
>>     return 1;
>> };
>> 
>> 
>> Output:
>> ### `SHOW_ERROR = 0`
>> ```ll
>> ; ModuleID = 'Module'
>> source_filename = "Module"
>> 
>> define i64 @f(i32 addrspace(42)*, i32 addrspace(1)*) {
>> entry:
>>   %slot = getelementptr i32, i32 addrspace(1)* %1, i64 1
>>   %slot_typed = bitcast i32 addrspace(1)* %slot to i64 addrspace(1)*
>>   %Val = load i64, i64 addrspace(1)* %slot_typed
>>   ret i64 %Val
>> }
>> ```
>> 
>> ### `SHOW_ERROR = 1`
>> ```
>> Slot(original):   %slot = getelementptr i32, i32 addrspace(42)* %0, i64 1
>> Slot(replaced):   %slot = getelementptr i32, i32 addrspace(1)* %1, i64 1
>> Assertion failed: (castIsValid(op, S, Ty) && "Invalid cast!"), function Create, file /Users/bollu/work/LLVM-all/polly/llvm/lib/IR/Instructions.cpp, line 2592.
>> [5]    56333 abort      ./prog
>> ```
>> 
>> Thanks,
>> ~Siddharth.
>> -- 
>> Sending this from my phone, please excuse any typos!
> 
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> 
> -- 
> Sending this from my phone, please excuse any typos!

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