[Patch, mips] Fix compiler abort with -mips32r2 -mips16 -msynci

["Steve Ellcey " <sellcey at mips dot com>]

While working on my favorite mips option (-msynci) I noticed an odd thing.
If I compile with '-mips32 -mips16 -msynci' I got a warning about synci not
being supported but if I compiled with '-mips32r2 -mips16 -msynci' I did not
get a warning, even though -mips16 mode does not support synci.  Furthermore
if I compiled a program that called __builtin___clear_cache with '-mips32r2
-mips16 -msynci', the compiler would abort.

In mips.h we have:

/* ISA includes synci, jr.hb and jalr.hb.  */
#define ISA_HAS_SYNCI ((ISA_MIPS32R2            \
                        || ISA_MIPS64R2)        \
                       && !TARGET_MIPS16)

What I found was that in mips_option_override, where we check this macro
to generate the warning we have this code at the front of the function:

  /* Process flags as though we were generating non-MIPS16 code.  */
  mips_base_mips16 = TARGET_MIPS16;
  target_flags &= ~MASK_MIPS16;

Then later, we check ISA_HAS_SYNCI, but at that point TARGET_MIPS16 is
always false because of the above lines.

I looked at changing ISA_HAS_SYNCI to use target_flag_explicit but that
seems like the wrong thing to do for the use of ISA_HAS_SYNCI in mips.md.
Then I modified the if statement in mips_option_override but that resulted
in the use of 'mips32r2 -mips16 -msynci' giving an odd warning message:

warning: the âmips32r2â architecture does not support the synci instruction

But of course mips32r2 does support synci, it is -mips16 that does not.  So I
added a new if statement with an explicit check against mips_base_mips16 to
give a better warning.

OK to checkin?

Steve Ellcey
sellcey@mips.com



2012-07-17  Steve Ellcey  <sellcey@mips.com>

	* config/mips/mips.c (mips_option_override): Fix check for -mips16
	-msynci combination of flags.


diff --git a/gcc/config/mips/mips.c b/gcc/config/mips/mips.c
index 7356ce5..889cfb5 100644
--- a/gcc/config/mips/mips.c
+++ b/gcc/config/mips/mips.c
@@ -16212,6 +16212,14 @@ mips_option_override (void)
       target_flags &= ~MASK_SYNCI;
     }
 
+  /* ISA_HAS_SYNCI checks TARGET_MIPS16 but that was turned off at the
+     beginning of this function so we need to check mips_base_mips16.  */
+  if (TARGET_SYNCI && mips_base_mips16)
+    {
+      warning (0, "the \'mips16\' ASE does not support the synci instruction");
+      target_flags &= ~MASK_SYNCI;
+    }
+
   /* Only optimize PIC indirect calls if they are actually required.  */
   if (!TARGET_USE_GOT || !TARGET_EXPLICIT_RELOCS)
     target_flags &= ~MASK_RELAX_PIC_CALLS;