[PATCH] x86 inline-asm: error-out on a 64-bit variable bound to a single register in 32-bit mode

[Eric Christopher]

You'll want to split out the new contraints for input size into a separate
patch. (And just commit it).
A small comment of why we're ignoring dependent types would be good.

One question: Why not just add all of the contraints first rather than
piecemeal as you get testcases? (Related to the comment above).

Thanks!

-eric

On Fri Aug 29 2014 at 4:46:37 PM Akira Hatanaka <ahatanak at gmail.com> wrote:

> Does the latest patch look fine? I am working on another patch which fixes
> a similar bug and I need to commit this patch first.
>
>
> On Thu, Aug 28, 2014 at 10:08 AM, Akira Hatanaka <ahatanak at gmail.com>
> wrote:
>
>> Latest version of the patch is attached which fixes a couple of
>> oversights. I had to add a line which checks whether Ty is a dependent type
>> before getTypeSize is called. Also, in the test case, "=" was missing
>> before constraint "a", so fixed that too.
>>
>> On Wed, Aug 27, 2014 at 3:22 PM, Reid Kleckner <rnk at google.com> wrote:
>>
>>> New patch looks good to me.
>>>
>>> It sounds like we have two cases of size mismatch:
>>> - The output operand lvalue is smaller than the constraint, meaning the
>>> store will write out of bounds. Your patch adds this.
>>> - The output operand lvalue is bigger than the constraint, meaning the
>>> whole value won't be initialized. We currently warn here via
>>> validateConstraintModifier.
>>>
>>> This code probably deserves some cleanup, but your patch is consistent
>>> with what we do for input operands, so let's go with that.
>>>
>>>
>> The reason llvm is crashing in the backend is that it's trying to use a
>> 64-bit register in 32-bit mode. It's not because a store is writing out of
>> bounds or there is a value left uninitialized. In the test case, if we
>> declare the variable bound to constraint "=a" to be a unit32_t or an
>> integer type that is smaller than 32-bit, clang compiles the program fine.
>>
>>
>>>
>>> On Wed, Aug 27, 2014 at 12:35 PM, Akira Hatanaka <ahatanak at gmail.com>
>>> wrote:
>>>
>>>> The commit log in r166737 doesn't say much about why this is a warning
>>>> instead of an error, but I know there are cases where warnings are needed.
>>>> For example, clang has to issue warnings instead of errors for the
>>>> inline-asm statements in the test case committed in r216260. If it's not
>>>> desirable to change validateConstraintModifier, we can add a function which
>>>> checks the output size that is similar to validateInputSize in r167717 (see
>>>> attached patch), which was suggested in the post-commit review.
>>>>
>>>>
>>>> http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20121112/067945.html
>>>>
>>>> I am not sure whether we can use fixit in this case. Fixit hints should
>>>> be used only if we know the user's intent and it's very clear that applying
>>>> the fixit hint is the right thing to do. Changing the type of variable "r"
>>>> to a 32-bit int will avoid crashing, but it doesn't look like that's what
>>>> the user wants.
>>>>
>>>> On Mon, Aug 25, 2014 at 6:20 PM, Reid Kleckner <rnk at google.com> wrote:
>>>>
>>>>> Can you investigate why we are warning in the first place? I think we
>>>>> should either only warn or only error. Currently we have a warning with a
>>>>> fixit but we don't recover as though we had applied the fixit. If we did
>>>>> that, we would not crash.
>>>>>
>>>>> In addition to the Clang-side changes, LLVM should probably be
>>>>> returning an error or reporting a fatal error instead of hitting
>>>>> unreachable.
>>>>>
>>>>>
>>>>>  On Mon, Aug 25, 2014 at 2:10 PM, Akira Hatanaka <ahatanak at gmail.com>
>>>>> wrote:
>>>>>
>>>>>>  Rebased patches attached.
>>>>>>
>>>>>> I also made changes to the clang patch so that clang can error-out
>>>>>> after a size mismatch is found as soon as
>>>>>> possible.TargetInfo::validateConstraintModifier has an extra parameter
>>>>>> IsError, which is set when it decides there is no point in continuing
>>>>>> compilation and it should stop compilation immediately. The error message
>>>>>> clang prints looks better than lllvm's message, but if it isn't right to
>>>>>> change the warning to an error, then I guess we have to detect the error
>>>>>> later just before isel, as is done in the llvm patch.
>>>>>>
>>>>>> On Wed, Jul 23, 2014 at 3:56 PM, Akira Hatanaka <ahatanak at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> llvm should error-out when a 64-bit variable is bound to a single
>>>>>>> register in x86 32-bit mode, but ToT clang/llvm fails to detect this error
>>>>>>> and continues compilation until it crashes in type-legalization:
>>>>>>>
>>>>>>> $ llc test/CodeGen/X86/inline-asm-regsize.ll  -O3
>>>>>>> -mtriple=i386-apple-darwin -o -
>>>>>>>
>>>>>>> inline-asm-regsize.ll  -O3 -mtriple=i386-apple-darwin -o -
>>>>>>>
>>>>>>> .section __TEXT,__text,regular,pure_instructions
>>>>>>>
>>>>>>> ExpandIntegerResult #0: 0x7fa2d1041728: i64 = Register %RCX [ID=0]
>>>>>>>
>>>>>>>
>>>>>>> Do not know how to expand the result of this operator!
>>>>>>>
>>>>>>> UNREACHABLE executed at
>>>>>>> /Users/ahatanaka/projects/llvm/git/llvm3/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp:1116!
>>>>>>>
>>>>>>> The attached patch fixes llvm to error-out and print this error
>>>>>>> message:
>>>>>>>
>>>>>>> error: Cannot bind a variable larger than 32-bit to a single
>>>>>>> register in 32-bit mode
>>>>>>>
>>>>>>>
>>>>>>> My initial solution was to have clang detect this error in
>>>>>>> TargetInfo::validateConstraintModifier. However, the code in
>>>>>>> SemaStmtAsm.cpp has to be changed to error-out instead of issuing a
>>>>>>> warning, which I wasn't sure was the right thing to do. I am attaching this
>>>>>>> patch too in case someone has a suggestion or an opinion on it.
>>>>>>>
>>>>>>> <rdar://problem/17476970>
>>>>>>>
>>>>>>>
>>>>>>
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>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>>
>>
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