[Bug target/40983] The scheduler incorrectly swaps MMX and floating point instructions

["ubizjak at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #3 from ubizjak at gmail dot com  2009-08-06 10:47 -------
Hm, we can fix this by teaching scheduler that every access to %mm registers
clobbers FP state. Since scheduler already depend all x87 instructions on
Top-Of-Stack (TOS) register, we can perhaps extend this requirement for all
instructions that use %mm reg.

Something like the proof-of-concept patch bellow:

--cut here--
Index: sched-deps.c
===================================================================
--- sched-deps.c        (revision 150503)
+++ sched-deps.c        (working copy)
@@ -1898,7 +1898,12 @@
            sched_analyze_reg (deps, FIRST_STACK_REG, mode, code, insn);
          sched_analyze_reg (deps, FIRST_STACK_REG, mode, USE, insn);
        }
+
+#ifdef FIRST_MMX_REG
+      if (regno >= FIRST_MMX_REG && regno <= LAST_MMX_REG)
+       sched_analyze_reg (deps, FIRST_STACK_REG, VOIDmode, CLOBBER, insn);
 #endif
+#endif
     }
   else if (MEM_P (dest))
     {
@@ -2044,7 +2049,12 @@
            sched_analyze_reg (deps, FIRST_STACK_REG, mode, USE, insn);
          sched_analyze_reg (deps, FIRST_STACK_REG, mode, SET, insn);
        }
+
+#ifdef FIRST_MMX_REG
+      if (regno >= FIRST_MMX_REG && regno <= LAST_MMX_REG)
+       sched_analyze_reg (deps, FIRST_STACK_REG, VOIDmode, CLOBBER, insn);
 #endif
+#endif

        if (cslr_p && sched_deps_info->finish_rhs)
          sched_deps_info->finish_rhs ();
--cut here--

Otherwise, you can just add "asm volatile ("")" as a scheduling barrier.


-- 

ubizjak at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2009-08-06 10:47:08
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40983