On 01/17/13 03:39, Bin.Cheng wrote:
On Thu, Jan 17, 2013 at 1:29 AM, Jan Hubicka <hubi...@ucw.cz> wrote:
Basic blocks 8/9/10 are identical and live until pass jump2, which is
after register allocation.
I think these duplicated BBs do not contain additional information and
should be better to be removed ASAP, because they might interfere with
other passes like ifcvt.
So should this issue be handled like in jump pass?
In this case, I'd expect DCE to optimize away the redundant assignments.
Yeah, we also used to be able to optimize these out in crossjumping before
regalloc but with SSA we now produce different pseudos in different copies so I
think it was path by Steven that disabled crossjumping proir jump2 (both passes
also ought to be renamed)
Unfortunately, this case can't be handled by DCE because just before
pass pass_into_cfg_layout_mode, the rtl is like:
1: NOTE_INSN_DELETED
9: NOTE_INSN_BASIC_BLOCK 2
2: r113:SI=r0:SI
3: r114:SI=r1:SI
4: NOTE_INSN_FUNCTION_BEG
11: pc={(r113:SI==0)?L39:pc}
REG_BR_PROB 0x3f6
12: NOTE_INSN_BASIC_BLOCK 4
13: r111:SI=zero_extend([r113:SI])
14: pc={(r111:SI==0x2d)?L43:pc}
REG_BR_PROB 0x7c7
15: NOTE_INSN_BASIC_BLOCK 5
16: pc={(r114:SI!=0)?L20:pc}
REG_BR_PROB 0x1388
22: L22:
17: NOTE_INSN_BASIC_BLOCK 6
6: r110:SI=0
18: pc=L24
19: barrier
20: L20:
21: NOTE_INSN_BASIC_BLOCK 7
23: pc={(r111:SI!=0x2b)?L22:pc}
REG_BR_PROB 0x1f49
35: NOTE_INSN_BASIC_BLOCK 8
8: r110:SI=0x1
36: pc=L24
37: barrier
39: L39:
38: NOTE_INSN_BASIC_BLOCK 9
7: r110:SI=0x1
40: pc=L24
41: barrier
43: L43:
42: NOTE_INSN_BASIC_BLOCK 10
5: r110:SI=0x1
24: L24:
25: NOTE_INSN_BASIC_BLOCK 11
26: r112:SI=r110:SI
30: r0:SI=r112:SI
33: use r0:SI
Insns 36/40 is deleted in pass pass_into_cfg_layout_mode to make each
edge possibly fall-through. The edges <8, 11> and <9, 11> still exist
in control flow and insns 7/8 are not dead code. It's just coincident
to have three identical basic blocks here. I don't think any passes
other than cross-jumping can handle this, right?
Right. This has to be caught by tail merging/cross jumping which occurs
during jump2.
jeff
