https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101023
Bug ID: 101023
Summary: [11/12 Regression] wrong code with -mstackrealign
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: zsojka at seznam dot cz
Target Milestone: ---
Host: x86_64-pc-linux-gnu
Target: x86_64-pc-linux-gnu
Created attachment 50981
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50981&action=edit
auto-reduced testcase (from OpenTTD sources)
Compiler output:
$ x86_64-pc-linux-gnu-g++ -O2 -mtune=opteron -mstackrealign
--param=hot-bb-frequency-fraction=1 testcase.C -S
The offending code is:
.L8:
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
movq %r12, -8(%rbp)
pushq %rax
the "push" overwrites r12 stored just one instruction above; when returning:
movq -8(%rbp), %r12
xorl %eax, %eax
leave
.cfi_def_cfa 7, 8
ret
the wrong data is restored to r12
I wasn't able yet to generate an executable testcase, but I can try to if
needed. (it shouldn't be that hard, just r12 needs to be used by the caller
during the call)
$ x86_64-pc-linux-gnu-g++ -v
Using built-in specs.
COLLECT_GCC=/repo/gcc-trunk/binary-latest-amd64/bin/x86_64-pc-linux-gnu-g++
COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-r12-1366-20210610095751-g6fcba9ef23e-checking-yes-rtl-df-extra-nobootstrap-amd64/bin/../libexec/gcc/x86_64-pc-linux-gnu/12.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /repo/gcc-trunk//configure --enable-languages=c,c++
--enable-valgrind-annotations --disable-nls --enable-checking=yes,rtl,df,extra
--disable-bootstrap --with-cloog --with-ppl --with-isl
--build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu
--target=x86_64-pc-linux-gnu --with-ld=/usr/bin/x86_64-pc-linux-gnu-ld
--with-as=/usr/bin/x86_64-pc-linux-gnu-as --disable-libstdcxx-pch
--prefix=/repo/gcc-trunk//binary-trunk-r12-1366-20210610095751-g6fcba9ef23e-checking-yes-rtl-df-extra-nobootstrap-amd64
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.0.0 20210610 (experimental) (GCC)
