* doc/invoke.texi (Option Summary) <MMIX Options>: Document

	-mbranch-predict, -mreg-stack-fill-bug-workaround and their
	negatives.
	(MMIX Options): Ditto.  Fix item/itemx typo for -mno-zero-extend.
	* config/mmix/mmix.c (mmix_target_asm_function_prologue): Rework
	kludge for pre-october-14th mmix versions to handle new-found bug
	with PUSHJ/PUSHGO and the register stack.
	* config/mmix/mmix.h (struct machine_function): Rename member
	has_call_value_without_parameters to has_call_without_parameters.
	All referers changed.
	(TARGET_MASK_REG_STACK_FILL_BUG, TARGET_DEFAULT
	TARGET_MASK_BRANCH_PREDICT): New macros.
	(TARGET_SWITCHES): New options -mreg-stack-fill-bug-workaround,
	-mno-reg-stack-fill-bug-workaround.
	* config/mmix/mmix.md ("call"): Set struct machine member
	has_call_without_parameters.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@48558 138bc75d-0d04-0410-961f-82ee72b054a4

3 files changed, 64 insertions, 16 deletions

diff --git a/gcc/config/mmix/mmix.c b/gcc/config/mmix/mmix.c
index b23365a8c93..5f9b4a8f387 100644
--- a/gcc/config/mmix/mmix.c
+++ b/gcc/config/mmix/mmix.c
@@ -967,19 +967,51 @@ mmix_target_asm_function_prologue (stream, locals_size)
 
   mmix_highest_saved_stack_register = regno;
 
-  /* FIXME: A kludge for the MMIXware ABI.  The return value comes back in
-     L of the caller, not just the register number of the X field of
-     PUSH{J,GO}.  So we need to make L agree with that number if there's a
-     function call in this function that returns a value but takes no
-     parameters (if there were parameters, L would be set to at least the
-     first parameter register, $16).  A real solution includes a pass to
-     test that settings of $15 (MMIX_RETURN_VALUE_REGNUM for the MMIXware
-     ABI) dominate all function calls that return a value.  This could be
-     done in the planned machine_dep_reorg pass to rename all registers.  */
-  if (! TARGET_ABI_GNU && cfun->machine->has_call_value_without_parameters)
-    fprintf (stream, "\tSET %s,%s\n",
-	     reg_names[MMIX_RETURN_VALUE_REGNUM],
-	     reg_names[MMIX_RETURN_VALUE_REGNUM]);
+  /* FIXME: Remove this when a corrected mmix version is released.
+
+     This kludge is a work-around for a presumed bug in the mmix simulator
+     (reported to knuth-bug), all versions up and including "Version of 14
+     October 2001".  When the circular register stack fills up, the parts
+     that would be overwritten need to be written to memory.  If the
+     "filling" instruction is a PUSHJ or PUSHGO, rL == 0 afterwards.  That
+     precise condition (rS == rO && rL == 0) is the same as for an empty
+     register stack, which means no more data is written to memory for
+     that round.  A hack is to remove the "&& L!=0" from "@<Increase
+     rL@>=" in mmix-sim.w: the register stack isn't empty under normal
+     circumstances, unless SAVE or UNSAVE is used, interrupts are enabled
+     or cases where rS == rO and rL is explicitly written to 0 as in
+     "PUT rL,0".
+
+     A workaround is to make sure PUSHJ or PUSHGO isn't filling up the
+     register stac.  This is accomplished if $16 or higher is written
+     before the function call.  This doesn't happen from a leaf functions
+     of course.  For the MMIXware ABI, this can't happen if all called
+     functions have parameters, because parameters start at $16.
+     Otherwise, and for the GNU ABI, if any register $16 and up is used,
+     we can see if it's mentioned before any function-call without
+     parameters.  This isn't too important; the bug will probably be fixed
+     soon and there's an option to not emit the work-around code.  The
+     call-with-parameters kludge wouldn't be there if it hadn't been for
+     it being left-over from a previous mmix version.
+
+     The actual code makes sure any register stack fill happens as early
+     as in the function prologue with a "SET $16,$16" (essentially a nop
+     except for the effects on the register stack).  */
+  if (TARGET_REG_STACK_FILL_BUG
+      && ((TARGET_ABI_GNU && !leaf_function_p ())
+	  || (!TARGET_ABI_GNU
+	      && cfun->machine->has_call_without_parameters)))
+    {
+      /* We don't have a specific macro or derivable expression for the
+	 first non-call-saved register.  If we need it in other places
+	 than here (which is temporary code anyway), such a macro should
+	 be added.  */
+      int flush_regno
+	= TARGET_ABI_GNU ? mmix_highest_saved_stack_register + 2 : 16;
+
+      fprintf (stream, "\tSET %s,%s\n",
+	       reg_names[flush_regno], reg_names[flush_regno]);
+    }
 }
 
 /* TARGET_ASM_FUNCTION_EPILOGUE.  */
diff --git a/gcc/config/mmix/mmix.h b/gcc/config/mmix/mmix.h
index bcc96f7c06a..32fa0e9300a 100644
--- a/gcc/config/mmix/mmix.h
+++ b/gcc/config/mmix/mmix.h
@@ -90,7 +90,7 @@ extern struct rtx_def *mmix_compare_op1;
    mmix.md too.  */
 struct machine_function
  {
-   int has_call_value_without_parameters;
+   int has_call_without_parameters;
    int has_landing_pad;
  };
 
@@ -157,6 +157,7 @@ extern int target_flags;
 #define TARGET_MASK_KNUTH_DIVISION 16
 #define TARGET_MASK_TOPLEVEL_SYMBOLS 32
 #define TARGET_MASK_BRANCH_PREDICT 64
+#define TARGET_MASK_REG_STACK_FILL_BUG 128
 
 /* FIXME: Get rid of this one.  */
 #define TARGET_LIBFUNC (target_flags & TARGET_MASK_LIBFUNCS)
@@ -166,8 +167,11 @@ extern int target_flags;
 #define TARGET_KNUTH_DIVISION (target_flags & TARGET_MASK_KNUTH_DIVISION)
 #define TARGET_TOPLEVEL_SYMBOLS (target_flags & TARGET_MASK_TOPLEVEL_SYMBOLS)
 #define TARGET_BRANCH_PREDICT (target_flags & TARGET_MASK_BRANCH_PREDICT)
+#define TARGET_REG_STACK_FILL_BUG \
+ (target_flags & TARGET_MASK_REG_STACK_FILL_BUG)
 
-#define TARGET_DEFAULT TARGET_MASK_BRANCH_PREDICT
+#define TARGET_DEFAULT \
+ (TARGET_MASK_BRANCH_PREDICT | TARGET_MASK_REG_STACK_FILL_BUG)
 
 /* FIXME: Provide a way to *load* the epsilon register.  */
 #define TARGET_SWITCHES							\
@@ -198,6 +202,12 @@ extern int target_flags;
    N_("Use P-mnemonics for branches statically predicted as taken")},	\
   {"no-branch-predict",	-TARGET_MASK_BRANCH_PREDICT,			\
    N_("Don't use P-mnemonics for branches")},				\
+  {"reg-stack-fill-bug-workaround",	TARGET_MASK_REG_STACK_FILL_BUG,	\
+   N_("Work around inconsistent behavior when a PUSHJ or PUSHGO\
+ instruction fills the register stack")},				\
+  {"no-reg-stack-fill-bug-workaround",	-TARGET_MASK_REG_STACK_FILL_BUG,\
+   N_("Don't work around inconsistent behavior when a PUSHJ or PUSHGO\
+ instruction fills the register stack")},	\
   {"",			TARGET_DEFAULT, ""}}
 
 /* Unfortunately, this must not reference anything in "mmix.c".  */
diff --git a/gcc/config/mmix/mmix.md b/gcc/config/mmix/mmix.md
index 7d1ae48401a..08ee0b309a4 100644
--- a/gcc/config/mmix/mmix.md
+++ b/gcc/config/mmix/mmix.md
@@ -995,6 +995,12 @@ DIVU %1,%1,%2\;GET %0,:rR\;NEGU %2,0,%0\;CSNN %0,$255,%2")
      error too.  */
   if (operands[2] == NULL_RTX)
     operands[2] = const0_rtx;
+
+  /* FIXME: Documentation bug: operands[3] (operands[2] for 'call') is the
+     *next* argument register, not the number of arguments in registers.  */
+  cfun->machine->has_call_without_parameters
+    |= REG_P (operands[2]) && REGNO (operands[2]) == MMIX_FIRST_ARG_REGNUM;
+
   operands[4] = gen_rtx_REG (DImode, MMIX_INCOMING_RETURN_ADDRESS_REGNUM);
 }")
 
@@ -1020,7 +1026,7 @@ DIVU %1,%1,%2\;GET %0,:rR\;NEGU %2,0,%0\;CSNN %0,$255,%2")
 
   /* FIXME: Documentation bug: operands[3] (operands[2] for 'call') is the
      *next* argument register, not the number of arguments in registers.  */
-  cfun->machine->has_call_value_without_parameters
+  cfun->machine->has_call_without_parameters
     |= REG_P (operands[3]) && REGNO (operands[3]) == MMIX_FIRST_ARG_REGNUM;
 
   operands[5] = gen_rtx_REG (DImode, MMIX_INCOMING_RETURN_ADDRESS_REGNUM);