diff mbox series

[1/5] cris: Don't default to -mmul-bug-workaround

Message ID 20220202002221.218BE20438@pchp3.se.axis.com
State Committed
Commit 4c4d0af4c94ccf0cfa74c8b13b8ec1029f57cd63
Headers
Series A few CRIS port improvements |

Commit Message

Hans-Peter Nilsson Feb. 2, 2022, 12:22 a.m. UTC 
  This flips the default for the errata handling for an old version
(TL;DR: workaround: no multiply instruction last on a cache-line).
Newer versions of the CRIS cpu don't have that bug.  While the impact
of the workaround is very marginal (coremark: less than .05% larger,
less than .0005% slower) it's an irritating pseudorandom factor when
assessing the impact of other changes.

Also, fix a wart requiring changes to more than TARGET_DEFAULT to flip
the default.

People building old kernels or operating systems to run on
ETRAX 100 LX are advised to pass "-mmul-bug-workaround".

gcc:
	* config/cris/cris.h (TARGET_DEFAULT): Don't include MASK_MUL_BUG.
	(MUL_BUG_ASM_DEFAULT): New macro.
	(MAYBE_AS_NO_MUL_BUG_ABORT): Define in terms of MUL_BUG_ASM_DEFAULT.
	* doc/invoke.texi (CRIS Options, -mmul-bug-workaround): Adjust
	accordingly.
---
 gcc/config/cris/cris.h | 19 ++++++++++++++++---
 gcc/doc/invoke.texi    |  2 +-
 2 files changed, 17 insertions(+), 4 deletions(-)
diff mbox series

Patch

diff --git a/gcc/config/cris/cris.h b/gcc/config/cris/cris.h
index b274e1166203..9245d7886929 100644
--- a/gcc/config/cris/cris.h
+++ b/gcc/config/cris/cris.h
@@ -153,7 +153,9 @@  extern int cris_cpu_version;
 
 #ifdef HAVE_AS_NO_MUL_BUG_ABORT_OPTION
 #define MAYBE_AS_NO_MUL_BUG_ABORT \
- "%{mno-mul-bug-workaround:-no-mul-bug-abort} "
+ "%{mno-mul-bug-workaround:-no-mul-bug-abort} " \
+ "%{mmul-bug-workaround:-mul-bug-abort} " \
+ "%{!mmul-bug-workaround:%{!mno-mul-bug-workaround:" MUL_BUG_ASM_DEFAULT "}} "
 #else
 #define MAYBE_AS_NO_MUL_BUG_ABORT
 #endif
@@ -255,15 +257,26 @@  extern int cris_cpu_version;
  (MASK_SIDE_EFFECT_PREFIXES + MASK_STACK_ALIGN \
   + MASK_CONST_ALIGN + MASK_DATA_ALIGN \
   + MASK_ALIGN_BY_32 \
-  + MASK_PROLOGUE_EPILOGUE + MASK_MUL_BUG)
+  + MASK_PROLOGUE_EPILOGUE)
 # else  /* 0 */
 #  define TARGET_DEFAULT \
  (MASK_SIDE_EFFECT_PREFIXES + MASK_STACK_ALIGN \
   + MASK_CONST_ALIGN + MASK_DATA_ALIGN \
-  + MASK_PROLOGUE_EPILOGUE + MASK_MUL_BUG)
+  + MASK_PROLOGUE_EPILOGUE)
 # endif
 #endif
 
+/* Don't depend on the assembler default setting for the errata machinery;
+   always pass the option to turn it on or off explicitly.  But, we have to
+   decide on which is the *GCC* default, and for that we should only need to
+   consider what's in TARGET_DEFAULT; no other changes should be necessary.  */
+
+#if (TARGET_DEFAULT & MASK_MUL_BUG)
+#define MUL_BUG_ASM_DEFAULT "-mul-bug-abort"
+#else
+#define MUL_BUG_ASM_DEFAULT "-no-mul-bug-abort"
+#endif
+
 /* Local, providing a default for cris_cpu_version.  */
 #define CRIS_DEFAULT_CPU_VERSION TARGET_CPU_DEFAULT
 
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index cfd415110cdf..7af5c51cc3c7 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -22268,7 +22268,7 @@  The options @option{-metrax4} and @option{-metrax100} are synonyms for
 @opindex mmul-bug-workaround
 @opindex mno-mul-bug-workaround
 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
-models where it applies.  This option is active by default.
+models where it applies.  This option is disabled by default.
 
 @item -mpdebug
 @opindex mpdebug