[Bug middle-end/39284] Computed gotos combined too aggressively

[hubicka at gcc dot gnu dot org]

------- Comment #11 from hubicka at gcc dot gnu dot org  2009-06-09 15:18 -------
Hmm, it is not exactly load.  In first case I get:

(code_label 12524 16482 12523 70 1249 "" [4 uses])

(note 12523 12524 149 70 [bb 70] NOTE_INSN_BASIC_BLOCK)

(insn:TI 149 12523 13690 70 ../src/Include/ceval-vm.i:47 (set (mem/c:SI
(plus:SI (reg/f:SI 6 bp)
                (const_int -64 [0xffffffffffffffc0])) [72 %sfp+-40 S4 A32])
        (const_int 1 [0x1])) 47 {*movsi_1} (expr_list:REG_EQUAL (const_int 1
[0x1])
        (nil)))

(insn 13690 149 1351 70 (set (reg/v:SI 0 ax [orig:155 why ] [155])
        (const_int 1 [0x1])) 47 {*movsi_1} (nil))

(code_label 1351 13690 1352 71 382 "" [0 uses])

(note 1352 1351 1353 71 [bb 71] NOTE_INSN_BASIC_BLOCK)

(jump_insn:TI 1353 1352 1354 71 ../src/Python/ceval.c:1000 (set (pc)
        (mem/c:SI (plus:SI (reg/f:SI 6 bp)
                (const_int -60 [0xffffffffffffffc4])) [72 %sfp+-36 S4 A32]))
640 {*indirect_jump} (nil))

(barrier 1354 1353 1477)


So there are 4 edges reaching WHY set.  In the second case it is move of WHY to
1:

(code_label 1363 1365 1349 150 384 "" [127 uses])

(note 1349 1363 1350 150 [bb 150] NOTE_INSN_BASIC_BLOCK)

(insn:TI 1350 1349 19980 150 ../src/Python/ceval.c:1000 (set (reg/v:SI 0 ax
[orig:155 why ] [155])
        (const_int 1 [0x1])) 47 {*movsi_1} (nil))

(note 19980 1350 19979 151 [bb 151] NOTE_INSN_BASIC_BLOCK)

(jump_insn 19979 19980 19982 151 ../src/Python/ceval.c:1000 (set (pc)
        (mem/c:SI (plus:SI (reg/f:SI 6 bp)
                (const_int -60 [0xffffffffffffffc4])) [72 %sfp+-36 S4 A32]))
640 {*indirect_jump} (nil))

(barrier 19982 19979 1373)


that prevents duplicating.  Probably ordirnary bb-reorder should be convincable
to handle this well?
This don't seem to happen at 64bit compilation.

I also posted the patch fixing optimize_for_size check


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39284