[Bug rtl-optimization/79149] bad optimization on MIPS and ARM leading to excessive stack usage in some cases
arnd at linaro dot org
gcc-bugzilla@gcc.gnu.org
Mon Feb 6 17:06:00 GMT 2017
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79149
--- Comment #11 from Arnd Bergmann <arnd at linaro dot org> ---
I've submitted a workaround for the kernel now, addressing the stack usage
warning on MIPS, as well as performance on ARM and others:
https://patchwork.kernel.org/patch/9555183/
The patch has two different workarounds, as I found that adding
-Wno-schedule-insns gives us the best results on the whirlpool512 code for both
stack size and performance by a wide margin, while -fsched-pressure is better
on stack size for "serpent" across architectures and compiler versions
However, it is interesting to notice that arm-linux-gnueabi-gcc-7 produces
worse
results with the serpent source code in terms of stack size with the default
"-fsched-pressure" ("press") than older versions, and worse than
-fno-schedule-insns (nosched):
default press nopress nosched
arm-linux-gnueabi-gcc-4.4.7 592 440
arm-linux-gnueabi-gcc-4.5.4 776 448 776 544
arm-linux-gnueabi-gcc-4.6.4 776 448 776 544
arm-linux-gnueabi-gcc-4.7.4 768 448 768 544
arm-linux-gnueabi-gcc-4.8.5 488 488 776 544
arm-linux-gnueabi-gcc-4.9.3 552 552 776 536
arm-linux-gnueabi-gcc-5.3.1 552 552 776 536
arm-linux-gnueabi-gcc-6.1.1 560 560 776 536
arm-linux-gnueabi-gcc-7.0.1 616 616 808 536
If we want to continue investigating this, I can try to construct a standalone
test case for performance testing on 'serpent' as well.
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