https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116229
Bug ID: 116229
Summary: wrong code at -Ofast aarch64 due to missing fneg to
generate 0x8000000000000000
Product: gcc
Version: 15.0
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: aarch64-unknown-linux-gnu
Created attachment 58828
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58828&action=edit
reduced testcase
Output:
$ aarch64-unknown-linux-gnu-gcc -Ofast testcase.c -static
$ qemu-aarch64 -- ./a.out
qemu: uncaught target signal 6 (Aborted) - core dumped
Aborted
Diff from -O3 to -Ofast shows the 0x8000000000000000 constant is not generated
(as -0.0):
$ diff -u a-testcase.s-O3 a-testcase.s-Ofast
--- a-testcase.s-O3 2024-08-04 20:07:06.417271286 +0200
+++ a-testcase.s-Ofast 2024-08-04 20:07:11.877241325 +0200
@@ -24,7 +24,7 @@
main:
.LFB1:
.cfi_startproc
- movi v0.4s, 0
+ movi v0.2d, 0
stp x29, x30, [sp, -48]!
.cfi_def_cfa_offset 48
.cfi_offset 29, -48
@@ -35,7 +35,6 @@
.cfi_offset 20, -24
adrp x20, .LC0
add x19, sp, 40
- fneg v0.2d, v0.2d
add x20, x20, :lo12:.LC0
bl foo
str d0, [sp, 40]
$ aarch64-unknown-linux-gnu-gcc -v
Using built-in specs.
COLLECT_GCC=/repo/gcc-trunk/binary-latest-aarch64/bin/aarch64-unknown-linux-gnu-gcc
COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-r15-2709-20240804001730-g7cd71c88637-checking-yes-rtl-df-extra-nobootstrap-aarch64/bin/../libexec/gcc/aarch64-unknown-linux-gnu/15.0.0/lto-wrapper
Target: aarch64-unknown-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
--with-sysroot=/usr/aarch64-unknown-linux-gnu --build=x86_64-pc-linux-gnu
--host=x86_64-pc-linux-gnu --target=aarch64-unknown-linux-gnu
--with-ld=/usr/bin/aarch64-unknown-linux-gnu-ld
--with-as=/usr/bin/aarch64-unknown-linux-gnu-as --enable-libsanitizer
--disable-libstdcxx-pch
--prefix=/repo/gcc-trunk//binary-trunk-r15-2709-20240804001730-g7cd71c88637-checking-yes-rtl-df-extra-nobootstrap-aarch64
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 15.0.0 20240804 (experimental) (GCC)
