From: Fredrik Noring Date: Tue, 27 Nov 2018 16:01:10 +0000 (+0000) Subject: MIPS: Add `-mfix-r5900' option for the R5900 short loop erratum X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=fb51a3a867e20f574bde3b929ec9ccfba6cc374b;p=gcc.git 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 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 --- diff --git a/gcc/ChangeLog b/gcc/ChangeLog index aea7767bde6..766fd4b6dd1 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,13 @@ +2018-11-27 Fredrik Noring + + * 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. + 2018-11-27 Jakub Jelinek PR target/88188 diff --git a/gcc/config/mips/mips.c b/gcc/config/mips/mips.c index 09b2ae72199..55b44078518 100644 --- a/gcc/config/mips/mips.c +++ b/gcc/config/mips/mips.c @@ -18908,13 +18908,13 @@ mips_reorg_process_insns (void) if (crtl->profile) cfun->machine->all_noreorder_p = false; - /* Code compiled with -mfix-vr4120, -mfix-rm7000 or -mfix-24k can't be - all noreorder because we rely on the assembler to work around some - errata. The R5900 too has several bugs. */ + /* Code compiled with -mfix-vr4120, -mfix-r5900, -mfix-rm7000 or + -mfix-24k can't be all noreorder because we rely on the assembler + to work around some errata. The R5900 target has several bugs. */ if (TARGET_FIX_VR4120 || TARGET_FIX_RM7000 || TARGET_FIX_24K - || TARGET_MIPS5900) + || TARGET_FIX_R5900) cfun->machine->all_noreorder_p = false; /* The same is true for -mfix-vr4130 if we might generate MFLO or @@ -20289,6 +20289,12 @@ mips_option_override (void) && strcmp (mips_arch_info->name, "r4400") == 0) target_flags |= MASK_FIX_R4400; + /* Default to working around R5900 errata only if the processor + was selected explicitly. */ + if ((target_flags_explicit & MASK_FIX_R5900) == 0 + && strcmp (mips_arch_info->name, "r5900") == 0) + target_flags |= MASK_FIX_R5900; + /* Default to working around R10000 errata only if the processor was selected explicitly. */ if ((target_flags_explicit & MASK_FIX_R10000) == 0 diff --git a/gcc/config/mips/mips.h b/gcc/config/mips/mips.h index 11ca364d752..d2205f08972 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} \ diff --git a/gcc/config/mips/mips.opt b/gcc/config/mips/mips.opt index 16c33d12e22..75332100435 100644 --- a/gcc/config/mips/mips.opt +++ b/gcc/config/mips/mips.opt @@ -165,6 +165,10 @@ mfix-r4400 Target Report Mask(FIX_R4400) Work around certain R4400 errata. +mfix-r5900 +Target Report Mask(FIX_R5900) +Work around the R5900 short loop erratum. + mfix-rm7000 Target Report Var(TARGET_FIX_RM7000) Work around certain RM7000 errata. diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 93938ab486b..682da942553 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -948,6 +948,7 @@ Objective-C and Objective-C++ Dialects}. -mmad -mno-mad -mimadd -mno-imadd -mfused-madd -mno-fused-madd -nocpp @gol -mfix-24k -mno-fix-24k @gol -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol +-mfix-r5900 -mno-fix-r5900 @gol -mfix-r10000 -mno-fix-r10000 -mfix-rm7000 -mno-fix-rm7000 @gol -mfix-vr4120 -mno-fix-vr4120 @gol -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol @@ -21290,7 +21291,8 @@ The processor names are: @samp{orion}, @samp{p5600}, @samp{p6600}, @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400}, -@samp{r4600}, @samp{r4650}, @samp{r4700}, @samp{r6000}, @samp{r8000}, +@samp{r4600}, @samp{r4650}, @samp{r4700}, @samp{r5900}, +@samp{r6000}, @samp{r8000}, @samp{rm7000}, @samp{rm9000}, @samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000}, @samp{sb1}, @@ -22082,6 +22084,16 @@ branch-likely instructions. @option{-mfix-r10000} is the default when @option{-march=r10000} is used; @option{-mno-fix-r10000} is the default otherwise. +@item -mfix-r5900 +@itemx -mno-fix-r5900 +@opindex mfix-r5900 +Do not attempt to schedule the preceding instruction into the delay slot +of a branch instruction placed at the end of a short loop of six +instructions or fewer and always schedule a @code{nop} instruction there +instead. The short loop bug under certain conditions causes loops to +execute only once or twice, due to a hardware bug in the R5900 chip. The +workaround is implemented by the assembler rather than by GCC@. + @item -mfix-rm7000 @itemx -mno-fix-rm7000 @opindex mfix-rm7000