https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104236
Bug ID: 104236
Summary: asm statements containing %= assembler templates
getting merged
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: bootstrap
Assignee: unassigned at gcc dot gnu.org
Reporter: ndesaulniers at google dot com
CC: bp at alien8 dot de, jpoimboe at redhat dot com,
pinskia at gcc dot gnu.org, segher at kernel dot
crashing.org
Target Milestone: ---
https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Volatile and
https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#AssemblerTemplate mention
> Under certain circumstances, GCC may duplicate (or remove duplicates
> of) your assembly code when optimizing. This can lead to unexpected
> duplicate symbol errors during compilation if your asm code defines
> symbols or labels. Using ‘%=’ (see AssemblerTemplate) may help resolve
> this problem.
>
> ‘%=’ Outputs a number that is unique to each instance of the asm
> statement in the entire compilation. This option is useful when
> creating local labels and referring to them multiple times in a single
> template that generates multiple assembler instructions.
I think I might have found a case where GCC is folding two asm strings that
look identical, but technically contain a %= assembler template. Perhaps
there's somewhere that checks for parameter equality, and misses checking
whether an asm string contains %= ? (or perhaps %= needs to be expanded
sooner?)
Test files are in:
https://gist.github.com/nickdesaulniers/c2c37edcdbaf3a2deb914d2ea8011a96
I would have expected the inline asm string containing `.Lreachable%=:` (in
media_request_object_complete()) to appear twice in the emitted asm output. If
I modify one of the two `.Lreachable` asm strings by one character, then I see
both emitted.
