https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109183
Bug ID: 109183
Summary: [regression?] since GCC 11.1, -MM -MMD generates "a-"
prefixed dependency files
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: preprocessor
Assignee: unassigned at gcc dot gnu.org
Reporter: yann at droneaud dot fr
Target Milestone: ---
I've found a rather surprising behavior change when using GCC >= 11.1 to build
some project using custom build environment.
How to reproduce:
: > test.c
gcc -MM -MMD test.c
test -e a-test.d && echo "unexpected dependency file name"
I've git-bisect-ed between GCC 11.1 and GCC 10.1 and the behavior change did
happen as the result of this commit:
commit 1dedc12d186a110854537e1279b4e6c29f2df35a
Author: Alexandre Oliva <ol...@adacore.com>
Date: Tue May 26 04:30:15 2020 -0300
revamp dump and aux output names
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=1dedc12d186a110854537e1279b4e6c29f2df35a
I didn't find an explanation there for this behavior change.
It's not noted in the documentation either
https://gcc.gnu.org/onlinedocs/gcc-11.3.0/gcc/Preprocessor-Options.html
So this make me believe it's some kind of regression for a corner case.
I understand the correct usage of -MMD is to be associated with some
processing, -E, -S, -c, etc, while -MM imply -E, so perhaps -MM and -MMD are
mutually exclusive and should not be allowed together. I dunno.
But generating "a-" prefixed dependency files is rather unexpected.
