While testing GCC on a 74k MIPS chip I noticed that by default the -mtune=74k*
flags cause GCC to not use the integer madd/msub instructions. According to
the checkin comments these were found to cause a performance hit over using
individual mult and add/sub instructions. I think there are some programs
though where using madd/msub would be a win on the 74k and I would like to
have a flag to allow users to override the default behaviour (either turning
it on for 74k or turning it off for other achitectures). This patch allows
-mimadd or -mno-imadd to override the default behaviour but does not change
that default behaviour.
OK for checkin?
Steve Ellcey
sell...@imgtec.com
2013-03-22 Steve Ellcey <sell...@mips.com>
* config/mips/mips.md (mimadd): New flag for integer madd/msub.
* config/mips/mips.h (GENERATE_MADD_MSUB): Check -mimadd flag.
diff --git a/gcc/config/mips/mips.h b/gcc/config/mips/mips.h
index 0acce14..62a7701 100644
--- a/gcc/config/mips/mips.h
+++ b/gcc/config/mips/mips.h
@@ -875,7 +875,9 @@ struct mips_cpu_info {
&& !TARGET_MIPS16)
/* Integer multiply-accumulate instructions should be generated. */
-#define GENERATE_MADD_MSUB (ISA_HAS_MADD_MSUB && !TUNE_74K)
+#define GENERATE_MADD_MSUB (ISA_HAS_MADD_MSUB \
+ && (target_flags_explicit & MASK_IMADD \
+ ? TARGET_IMADD : !TUNE_74K))
/* ISA has floating-point madd and msub instructions 'd = a * b [+-] c'. */
#define ISA_HAS_FP_MADD4_MSUB4 ISA_HAS_FP4
diff --git a/gcc/config/mips/mips.opt b/gcc/config/mips/mips.opt
index d8ef2e7..6b3024b 100644
--- a/gcc/config/mips/mips.opt
+++ b/gcc/config/mips/mips.opt
@@ -58,6 +58,10 @@ mmad
Target Report Var(TARGET_MAD)
Use PMC-style 'mad' instructions
+mimadd
+Target Report Mask(IMADD)
+Use integer madd/msub instructions
+
march=
Target RejectNegative Joined Var(mips_arch_option) ToLower
Enum(mips_arch_opt_value)
-march=ISA Generate code for the given ISA
