[Bug inline-asm/56148] [4.8 Regression] inline asm matching constraint with different mode

["steven at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56148

Steven Bosscher <steven at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |steven at gcc dot gnu.org

--- Comment #7 from Steven Bosscher <steven at gcc dot gnu.org> 2013-02-12 16:24:39 UTC ---
(in my previous post I of course mean inputs and constraints...)

Breaking down the insn once more in something that's more readable
to me at least:

(parallel [
   (set (reg:DI 63 [ a ]) (asm_in[0] (reg:SI 67) "0"))
   (set (reg:DI 64 [ c ]) (asm_in[1] (reg:DI 65) "mr"))
   (set (reg:DI 65 [ d ]) (asm_in[2] (reg:SI 69) "1"))
   (set (reg:DI 66 [ b ]) (asm_in[3] (reg:DI 65) "2"))
                          (asm_in[4] (reg:SI 67) "3")])

so
- r67:SI must match r63:DI
- r69:SI must match r64:DI
- r65:DI must match r65:DI
- r67:SI must match r66:DI

The last constraint comes from CSE, which transforms:

[   (reg:SI 67)
    (reg:DI 68)
    (reg:SI 69)
    (reg:DI 70)
    (reg:SI 71) ]

to

[   (reg:SI 67)
    (reg/f:DI 68)
    (reg:SI 69)
    (reg/f:DI 68)
    (reg:SI 67) ]

because r70 and r68 have the same value before CSE:

    6: {r68:DI=frame:DI-0x10;clobber flags:CC;}
    8: {r70:DI=frame:DI-0x10;clobber flags:CC;}

and CSE cleans that up:

    6: {r68:DI=frame:DI-0x10;clobber flags:CC;}
    8: r70:DI=r68:DI

Disabling or undoing that transformation makes the ICE disappear.
This is also in effect what old reload does with reload insn 21.