[PATCH] D99160: [X86][FastISEL] Support DW_TAG_call_site_parameter with FastISEL

[Alok Kumar Sharma via Phabricator via cfe-commits]

alok added a comment.

In D99160#2666068 <https://reviews.llvm.org/D99160#2666068>, @djtodoro wrote:

> In D99160#2666066 <https://reviews.llvm.org/D99160#2666066>, @alok wrote:
>
>> In D99160#2665580 <https://reviews.llvm.org/D99160#2665580>, @probinson wrote:
>>
>>> FastISel is normally used only at -O0, I wouldn't expect any parameters to be optimized out at -O0.
>>> The test is running llc with default optimization, which is -O2, and forcing fast-isel; this is not a usual combination and I wouldn't expect us to spend any effort making sure debug info works well with that combination.
>>>
>>> If flang is forcing fast-isel even with optimization, that sounds like a problem for flang to solve, not LLVM.
>>
>> Thanks for your comments. I am sorry as the earlier used options in test case were more confusing than helpful. I have changed that now.
>> The updated testcase at "-O0" with FastISel does have optimized out parameter, this is because generation of "DW_OP_GNU_entry_value" is enabled starting from "-O0". This causes llvm to generate it whenever it gets opportunity (more local variables to preserve may be the reason). 
>> The concern here is only DW_OP_GNU_entry_value is not sufficient and should be supported with "DW_TAG_GNU_call_site_parameter", which I tried in current patch.
>
>
>
>> "DW_OP_GNU_entry_value" is enabled starting from "-O0".
>
> I am wondering if this is true...

You can try with testcase attached with this patch.

bash$ llc -O0 -filetype=obj llvm/test/DebugInfo/X86/callsitepar-fastisel.ll -o callsitepar-fastisel.o
bash$ llvm-dwarfdump callsitepar-fastisel.o | grep DW_OP_GNU_entry_value

  [0x00000000000000bf, 0x0000000000000101): DW_OP_GNU_entry_value(DW_OP_reg4 RSI))


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