diff mbox

m68k: handle register conflict with PRE_DEC in notice_update_cc

Message ID mvmfvrt7a8p.fsf@hawking.suse.de
State New
Headers show

Commit Message

Andreas Schwab Oct. 22, 2013, 12:36 p.m. UTC 
When compiling libxml2 with -O2 -fomit-frame-pointer the following pair
of insns is generated:

(insn 113 112 114 (set (mem:SI (pre_dec:SI (reg/f:SI 15 %sp)) [0 S4 A16])
        (mem/c:SI (plus:SI (reg/f:SI 15 %sp)
                (const_int 44 [0x2c])) [5 strict+0 S4 A32])) xpath.i:269 38 {*movsi_m68k2}
     (expr_list:REG_ARGS_SIZE (const_int 12 [0xc])
        (nil)))
(insn 114 113 115 (set (cc0)
        (compare (mem/c:SI (plus:SI (reg/f:SI 15 %sp)
                    (const_int 44 [0x2c])) [5 inf+0 S4 A32])
            (const_int 0 [0]))) xpath.i:269 4 {*tstsi_internal_68020_cf}
     (nil))

For rtl_equal_p (mem/c:SI (plus:SI (reg/f:SI 15 %sp) (const_int 44
[0x2c])) [5 strict+0 S4 A32]) and (mem/c:SI (plus:SI (reg/f:SI 15 %sp)
(const_int 44 [0x2c])) [5 inf+0 S4 A32]) look the same, so
final_scan_insn thinks the latter insn is a redundant test.  But since
pre_dec has modified %sp the two mems refer to two different stack
slots.  notice_update_cc should not register the src operand in the
first insn as a CC status setter in this case.

Bootstrapped and tested on m68k-suse-linux, committed to trunk.

Andreas.

	* config/m68k/m68k.c (notice_update_cc): Handle register conflict
	with PRE_DEC.
diff mbox

Patch

diff --git a/gcc/config/m68k/m68k.c b/gcc/config/m68k/m68k.c
index 5e3236f..7035504 100644
--- a/gcc/config/m68k/m68k.c
+++ b/gcc/config/m68k/m68k.c
@@ -4209,6 +4209,13 @@  notice_update_cc (rtx exp, rtx insn)
       && cc_status.value2
       && reg_overlap_mentioned_p (cc_status.value1, cc_status.value2))
     cc_status.value2 = 0;
+  /* Check for PRE_DEC in dest modifying a register used in src.  */
+  if (cc_status.value1 && GET_CODE (cc_status.value1) == MEM
+      && GET_CODE (XEXP (cc_status.value1, 0)) == PRE_DEC
+      && cc_status.value2
+      && reg_overlap_mentioned_p (XEXP (XEXP (cc_status.value1, 0), 0),
+				  cc_status.value2))
+    cc_status.value2 = 0;
   if (((cc_status.value1 && FP_REG_P (cc_status.value1))
        || (cc_status.value2 && FP_REG_P (cc_status.value2))))
     cc_status.flags = CC_IN_68881;