[PATCH] D91607: [clang][Sparc] Fix __builtin_extract_return_addr etc.

Tue Feb 1 07:53:02 PST 2022

ro added a comment.

In D91607#3285825 <https://reviews.llvm.org/D91607#3285825>, @efriedma wrote:

> In D91607#3283350 <https://reviews.llvm.org/D91607#3283350>, @ro wrote:
>
>> In D91607#3280808 <https://reviews.llvm.org/D91607#3280808>, @efriedma wrote:
>>
>>> Testcase?
>>
>> I thought the 3 testcases adjusted in D91608 <https://reviews.llvm.org/D91608> to use `__builtin_extract_return_addr` and fixed by this patch were enough.  Otherwise, should I just augment `clang/test/CodeGen/builtins-sparc.c` or better create a new test?
>
> I'd prefer to have coverage in the clang regression tests, so developers can catch regressions and easily check the expected codegen.  builtins-sparc.c is fine.

Understood: this way you don't rely on native builds and can test SPARC V8 structure return which isn't exercised by the sanitzer tests.

>>> Do you need to ptrtoint/inttoptr?  I would expect that the address is an `i8*`, so you can just GEP an appropriate number of bytes.
>>
>> TBH, I know practically nothing about LLVM codegen, so I rely heavily on guidance.  IIRC this patch was developed by searching for similar code in `TargetInfo.cpp` and modifying it until it did what I needed.  Is this the place to read on GEP <https://llvm.org/docs/GetElementPtr.html>?
>
> That's a good starting place for understanding the complexity of GEP... but you don't need that much here. Here, we just want to pass a single index; that's equivalent to pointer addition in C.
>
> You should be able to just drop the calls to CreatePtrToInt and CreateIntToPtr, and replace CreateAdd with CreateGEP.

Cool: I'd been struggling with `CreateConstInBoundsByteGEP` which seemed what I need, but had me fighting with conversion between `llvm::Value *` and `Address`.

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https://reviews.llvm.org/D91607