[Bug target/39429] compiler create bad asm codes.

["mikpe at it dot uu dot se" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #8 from mikpe at it dot uu dot se  2009-07-13 13:05 -------
Mystery solved. Buried in revision 146451, which should just fix enum
conversions for C++ compatibility, is the following bug fix:

--- trunk/gcc/config/arm/arm.c  2009/04/20 19:30:55     146450
+++ trunk/gcc/config/arm/arm.c  2009/04/20 19:35:00     146451
@@ -7408,7 +7410,7 @@
       /* Don't accept any offset that will require multiple
         instructions to handle, since this would cause the
         arith_adjacentmem pattern to output an overlong sequence.  */
-      if (!const_ok_for_op (PLUS, val0) || !const_ok_for_op (PLUS, val1))
+      if (!const_ok_for_op (val0, PLUS) || !const_ok_for_op (val1, PLUS))
        return 0;

       /* Don't allow an eliminable register: register elimination can make

The parameters to const_ok_for_op had been swapped, causing this if statement
to not reject offsets that are awkward for ARM. Combined with a non-FL_LDSCHED
cpu type this enabled arith_adjacentmem for a bad offset, which forced it to
split the LDM into two LDRs, and that code fails to order the LDRs to avoid
clobbering the shared base register. With the above patch arith_adjacentmem
will not trigger for bad offsets, avoiding the broken LDM splitting code.

This patch is needed also for the 4.4 and 4.3 branches, and I've checked that
it fixes this test case there too.

It seems that there is a bit of redundancy between the adjacent_mem_locations
test and the arith_adjacentmem pattern. Both check const_ok_for_arm on the
offset and the negated offset. The first attempts to reject bad offsets, while
the second attempts to handle them. I'm not sure, but I _think_ that the code
in arith_adjacentmem to split an LDM into two LDRs is now dead (after the bug
fix above). However, just in case it isn't, I'm attaching a patch to correct
it.

Unrelated to this PR, buried in revision 146451 is another bug fix:

--- trunk/gcc/config/arm/arm.c  2009/04/20 19:30:55     146450
+++ trunk/gcc/config/arm/arm.c  2009/04/20 19:35:00     146451
@@ -5465,7 +5465,7 @@
       return true;

     case ABS:
-      if (GET_MODE_CLASS (mode == MODE_FLOAT))
+      if (GET_MODE_CLASS (mode) == MODE_FLOAT)
        {
          if (TARGET_HARD_FLOAT && (mode == SFmode || mode == DFmode))
            {

This one is also needed in 4.4, but not in 4.3.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39429