[patch, mips] Fix for PR 54619, GCC aborting with -O -mips16

[Steve Ellcey]

While building newlib with -O2 -mips16 I ran into a problem with GCC
aborting due to the compiler trying to execute '0 % 0' in
mips16_unextended_reference_p.  The problem was that the code checked
for BLKmode and skipped the modulo operation in that case because
GET_MODE_SIZE (BLKmode) is zero but it didn't check for VOIDmode whose
size is also zero.  Rather then add a check for VOIDmode I changed
the check to 'GET_MODE_SIZE (mode) != 0'.

While looking at the code I also noticed that if offset was zero then
we should return true even if mode is BLKmode or VOIDmode.  Returning
false would not generate bad code or cause problems but returning true
would result in better costing model in mips_address_insns so I made
that change too.

Tested on a mips elf target, OK to checkin?

Steve Ellcey
sell...@mips.com



2012-09-19  Steve Ellcey  <sell...@mips.com>

        PR target/54619
        * config/mips/mips.c (mips16_unextended_reference_p): Check for
        zero offset and zero size mode.


diff --git a/gcc/config/mips/mips.c b/gcc/config/mips/mips.c
index 7f9df4c..ecdb811 100644
--- a/gcc/config/mips/mips.c
+++ b/gcc/config/mips/mips.c
@@ -2230,7 +2230,10 @@ static bool
 mips16_unextended_reference_p (enum machine_mode mode, rtx base,
                               unsigned HOST_WIDE_INT offset)
 {
-  if (mode != BLKmode && offset % GET_MODE_SIZE (mode) == 0)
+  if (offset == 0)
+    return true;
+
+  if (GET_MODE_SIZE (mode) != 0 && offset % GET_MODE_SIZE (mode) == 0)
     {
       if (GET_MODE_SIZE (mode) == 4 && base == stack_pointer_rtx)
        return offset < 256U * GET_MODE_SIZE (mode);