Nick Desaulniers 3220022038 ARM: 9256/1: NWFPE: avoid compiler-generated __aeabi_uldivmod ... clang-15's ability to elide loops completely became more aggressive when it can deduce how a variable is being updated in a loop. Counting down one variable by an increment of another can be replaced by a modulo operation. For 64b variables on 32b ARM EABI targets, this can result in the compiler generating calls to __aeabi_uldivmod, which it does for a do while loop in float64_rem(). For the kernel, we'd generally prefer that developers not open code 64b division via binary / operators and instead use the more explicit helpers from div64.h. On arm-linux-gnuabi targets, failure to do so can result in linkage failures due to undefined references to __aeabi_uldivmod(). While developers can avoid open coding divisions on 64b variables, the compiler doesn't know that the Linux kernel has a partial implementation of a compiler runtime (--rtlib) to enforce this convention. It's also undecidable for the compiler whether the code in question would be faster to execute the loop vs elide it and do the 64b division. While I actively avoid using the internal -mllvm command line flags, I think we get better code than using barrier() here, which will force reloads+spills in the loop for all toolchains. Link: https://github.com/ClangBuiltLinux/linux/issues/1666 Reported-by: Nathan Chancellor <nathan@kernel.org> Reviewed-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Tested-by: Nathan Chancellor <nathan@kernel.org> Cc: stable@vger.kernel.org Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>		2022-11-07 14:19:02 +00:00
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ARM-gcc.h
ChangeLog
double_cpdo.c	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 61	2019-05-24 17:36:45 +02:00
entry.S	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 61	2019-05-24 17:36:45 +02:00
extended_cpdo.c	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 61	2019-05-24 17:36:45 +02:00
fpa11_cpdo.c	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 61	2019-05-24 17:36:45 +02:00
fpa11_cpdt.c	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 61	2019-05-24 17:36:45 +02:00
fpa11_cprt.c	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 61	2019-05-24 17:36:45 +02:00
fpa11.c	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 61	2019-05-24 17:36:45 +02:00
fpa11.h	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 61	2019-05-24 17:36:45 +02:00
fpa11.inl
fpmodule.c	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 61	2019-05-24 17:36:45 +02:00
fpmodule.h	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 61	2019-05-24 17:36:45 +02:00
fpmodule.inl
fpopcode.c	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 61	2019-05-24 17:36:45 +02:00
fpopcode.h	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 61	2019-05-24 17:36:45 +02:00
fpsr.h	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 61	2019-05-24 17:36:45 +02:00
Makefile	ARM: 9256/1: NWFPE: avoid compiler-generated __aeabi_uldivmod	2022-11-07 14:19:02 +00:00
milieu.h
single_cpdo.c	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 61	2019-05-24 17:36:45 +02:00
softfloat-macros
softfloat-specialize
softfloat.c
softfloat.h