[PATCH] D61600: [DebugInfo] More precise variable range for stack locations
Nikola Prica via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue May 7 01:03:18 PDT 2019
NikolaPrica marked an inline comment as done.
NikolaPrica added inline comments.
================
Comment at: lib/CodeGen/AsmPrinter/DwarfDebug.cpp:1359
+ // TODO: Add support for single value fragment locations.
+ if (Entries.size() == 1 && !MInsn->getDebugExpression()->isFragment()) {
+ const auto *End = HistoryMapEntries.back().isClobber()
----------------
dstenb wrote:
> It seems that this can give incorrect single value locations for cases where we have produced location list entries with empty ranges.
>
> For example:
>
> ```
> frame-setup PUSH64r undef $rax, implicit-def $rsp, implicit $rsp
> DBG_VALUE 123, $noreg, !12, !DIExpression(), debug-location !13
> DBG_VALUE 456, $noreg, !12, !DIExpression(), debug-location !13
> CALL64pcrel32 @foo, csr_64, implicit $rsp, implicit $ssp, implicit-def $rsp, implicit-def $ssp, debug-location !14
> $eax = XOR32rr undef $eax, undef $eax, implicit-def dead $eflags, debug-location !15
> $rcx = frame-destroy POP64r implicit-def $rsp, implicit $rsp, debug-location !15
> RETQ killed $eax, debug-location !15
> ```
>
> Here, the first debug value will result in a location list entry with an empty range, since it is immediately followed by the second, and such entries are omitted from the location list, resulting in a single entry in `Entries` for the constant value 456. However, `MInsn` is the first debug value, so we will create a single location description with the wrong value:
>
>
> ```
> 0x00000043: DW_TAG_variable
> DW_AT_const_value (123)
> ```
>
> I'm not sure what the check should be to avoid these sort of cases. Perhaps check that all debug value entries in `HistoryMapEntries` are described by the same location, and have the same expression?
Such check could be return value of `buildLocationList`? Or we can just take the last `DebugInstr` from `HistoryMapEntries` which could be the last entry or the entry before the last one?
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https://reviews.llvm.org/D61600/new/
https://reviews.llvm.org/D61600
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