http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47379
Summary: fwprop1 generates bad codes for x32
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: hjl.to...@gmail.com
On x32 branch, for
---
typedef unsigned IPos;
typedef unsigned char uch;
extern uch window[];
unsigned max_chain_length;
unsigned strstart;
int longest_match(IPos cur_match, int len, int best_len)
{
unsigned chain_length = max_chain_length;
register uch *scan = window + strstart;
register uch *match;
register uch scan_end1 = scan[best_len-1];
register uch scan_end = scan[best_len];
do {
;
match = window + cur_match;
if (match[best_len] != scan_end ||
match[best_len-1] != scan_end1 ||
*match != *scan ||
*++match != scan[1]) continue;
best_len = len;
} while ( --chain_length != 0);
return best_len;
}
---
compiled with -mx32 -O, fwprop1 pass turns:
(insn 14 13 15 2 (parallel [
(set (reg/f:SI 86)
(plus:SI (reg:SI 63 [ strstart.0 ])
(symbol_ref:SI ("window") [flags 0x40] <var_decl
0x7f7a44198000 window>)))
(clobber (reg:CC 17 flags))
]) x.i:9 253 {*addsi_1}
(nil))
(insn 15 14 16 2 (set (reg/v/f:DI 64 [ scan ])
(zero_extend:DI (reg/f:SI 86))) x.i:9 115 {*zero_extendsidi2_rex64}
(nil))
(insn 16 15 17 2 (set (reg:SI 65 [ best_len.1 ])
(reg/v:SI 85 [ best_len ])) x.i:11 64 {*movsi_internal}
(nil))
(insn 17 16 18 2 (parallel [
(set (reg:SI 89)
(plus:SI (reg/v:SI 85 [ best_len ])
(subreg/s/u:SI (reg/v/f:DI 64 [ scan ]) 0)))
(clobber (reg:CC 17 flags))
]) x.i:11 253 {*addsi_1}
(nil))
into
(insn 14 13 15 2 (parallel [
(set (reg/f:SI 86)
(plus:SI (reg:SI 63 [ strstart.0 ])
(symbol_ref:SI ("window") [flags 0x40] <var_decl
0x7f7a44198000 window>)))
(clobber (reg:CC 17 flags))
]) x.i:9 253 {*addsi_1}
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil)))
(insn 15 14 17 2 (set (reg/v/f:DI 64 [ scan ])
(zero_extend:DI (reg/f:SI 86))) x.i:9 115 {*zero_extendsidi2_rex64}
(expr_list:REG_DEAD (reg/f:SI 86)
(nil)))
(insn 17 15 18 2 (parallel [
(set (reg:SI 89)
(plus:SI (reg/v:SI 85 [ best_len ])
(reg/f:SI 86)))
(clobber (reg:CC 17 flags))
]) x.i:11 253 {*addsi_1}
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil)))
with
In insn 17, replacing
(subreg/s/u:SI (reg/v/f:DI 64 [ scan ]) 0)
with (reg/f:SI 86)
Changed insn 17
deferring rescan insn with uid = 17.
deferring rescan insn with uid = 17.
For x32, (subreg/s/u:SI (reg/v/f:DI 64 [ scan ]) 0) is
free while (reg/f:SI 86) is an extra register.
