Hello,
This patch fixes ICE in reload on the gcc testsuite.
Below is analysis of the problem:
(define_expand "cmpdi"
[(parallel
[(set (cc0)
(compare (match_operand:DI 0 "nonimmediate_operand" "")
(match_operand:DI 1 "general_operand" "")))
(clobber (match_dup 2))])]
""
"m68k_last_compare_had_fp_operands = 0; operands[2] = gen_reg_rtx
(DImode);")
(define_insn ""
[(set (cc0)
(compare (match_operand:DI 1 "nonimmediate_operand" "0,d")
(match_operand:DI 2 "general_operand" "d,0")))
(clobber (match_operand:DI 0 "register_operand" "=d,d"))]
...)
Here cmpdi expander creates a third operand, that, basically, is a
scratch register, and constraints in the instruction pattern specify
that one of the original operands should be placed in that register.
Reload then failures in find_reloads() on the following instruction
(both registers 30 and 31 are pseudos):
(insn 8 7 9 3 (parallel [
(set (cc0)
(compare (reg:DI 30 [ D.1179 ])
(const_double -1 [0xffffffff] 0 [0x0] 0 [0x0] 0
[0x0] 0 [0x0] 0 [0x0])))
(clobber (reg:DI 31))
]) 12 {*m68k.md:430} (nil))
What reload needs here to do is to generate move of const_double to
register 31, but, for some reason, it fails.
I speculate that the fact that the additional operand is not trivially
dead puts additional pressure on reload, which, combined with
restrictions of m68k being cc0 target (reload can't use output_reloads
for this pattern as it sets cc0) makes reload to fail.
The fix I come up with is to rewrite the expander and the pattern to
use (match_scratch) instead. It seems easier for reload to replace
(scratch) than to replace a pseudo with a hard register. And, in the
context of cmpdi instruction, pseudo and scratch are equivalent.
Tested on ColdFire bare-metal with no regression (gcc, g++ and
libstdc++ testsuites). Ok for trunk?