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| author | Fredrik Noring <noring@nocrew.org> | 2018-11-27 16:01:10 +0000 |
|---|---|---|
| committer | Maciej W. Rozycki <macro@gcc.gnu.org> | 2018-11-27 16:01:10 +0000 |
| commit | fb51a3a867e20f574bde3b929ec9ccfba6cc374b (patch) | |
| tree | 0add77034e2751dfbb9c5579e20fb2200edb6415 /gcc/config/mips/mips.h | |
| parent | 4d8da4df6b6c2c7b89a6cc402bc134b69911e922 (diff) | |
| download | gcc-fb51a3a867e20f574bde3b929ec9ccfba6cc374b.zip gcc-fb51a3a867e20f574bde3b929ec9ccfba6cc374b.tar.gz gcc-fb51a3a867e20f574bde3b929ec9ccfba6cc374b.tar.bz2 | |
MIPS: Add `-mfix-r5900' option for the R5900 short loop erratum
The short loop bug under certain conditions causes loops to
execute only once or twice, due to a hardware bug in the R5900 chip.
`-march=r5900' already enables the R5900 short loop workaround.
However, the R5900 ISA and most other MIPS ISAs are mutually
exclusive since R5900-specific instructions are generated as well.
The `-mfix-r5900' option can be used in combination with e.g.
`-mips2' or `-mips3' to generate generic MIPS binaries that also
work with the R5900 target. The workaround is implemented by GAS
rather than by GCC.
The following small `shortloop.c' file has been used as a test
with GCC 8.2.0:
void shortloop(void)
{
__asm__ __volatile__ (
" li $3, 300\n"
"loop:\n"
" addi $3, -1\n"
" addi $4, -1\n"
" bne $3, $0, loop\n"
" li $4, 3\n"
::);
}
The following six combinations have been tested:
% mipsr5900el-unknown-linux-gnu-gcc -O1 -c shortloop.c
% mipsr5900el-unknown-linux-gnu-gcc -O1 -c shortloop.c -mfix-r5900
% mipsr5900el-unknown-linux-gnu-gcc -O1 -c shortloop.c -mno-fix-r5900
% mipsr4000el-unknown-linux-gnu-gcc -O1 -c shortloop.c
% mipsr4000el-unknown-linux-gnu-gcc -O1 -c shortloop.c -mfix-r5900
% mipsr4000el-unknown-linux-gnu-gcc -O1 -c shortloop.c -mno-fix-r5900
The R5900 short loop erratum is corrected in exactly three cases:
1. for the target `mipsr5900el' by default;
2. for the target `mipsr5900el' with `-mfix-r5900';
3. for any other MIPS target (e.g. `mipsr4000el') with `-mfix-r5900'.
In all other cases the correction is not made.
2018-11-27 Fredrik Noring <noring@nocrew.org>
gcc/
* config/mips/mips.c (mips_reorg_process_insns)
(mips_option_override): Handle `-mfix-r5900'.
* config/mips/mips.h (ASM_SPEC): Add `mfix-r5900' and
`mno-fix-r5900'.
* config/mips/mips.opt (mfix-r5900): New option.
* doc/invoke.texi: Document the `r5900' processor name, and
`-mfix-r5900' and `-mno-fix-r5900' options.
From-SVN: r266519
Diffstat (limited to 'gcc/config/mips/mips.h')
| -rw-r--r-- | gcc/config/mips/mips.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/gcc/config/mips/mips.h b/gcc/config/mips/mips.h index 11ca364..d2205f0 100644 --- a/gcc/config/mips/mips.h +++ b/gcc/config/mips/mips.h @@ -1411,6 +1411,7 @@ struct mips_cpu_info { %{mloongson-ext2} %{mno-loongson-ext2} \ %{msmartmips} %{mno-smartmips} \ %{mmt} %{mno-mt} \ +%{mfix-r5900} %{mno-fix-r5900} \ %{mfix-rm7000} %{mno-fix-rm7000} \ %{mfix-vr4120} %{mfix-vr4130} \ %{mfix-24k} \ |