replaceUsesOfWith does not keep addrspace info consistent. Flip boolean value SHOW_ERROR to demonstrate error.

main.cpp

#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.md

SHOW_ERROR = 0

; 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