------- Comment #3 from rguenth at gcc dot gnu dot org 2006-10-09 14:58 -------
Confirmed. Ok for x86_64:
f:
.LFB2:
movslq %edi,%rdi
movslq %esi,%rsi
imulq %rdi, %rsi
sarq $15, %rsi
movl %esi, %eax
ret
We are expanding (int) ((long long int) b * (long long int) a >> 15).
We split
(insn:HI 11 31 12 2 (parallel [
(set (reg:DI 0 ax [62])
(mult:DI (sign_extend:DI (reg/v:SI 0 ax [orig:60 b ] [60]))
(sign_extend:DI (mem/c/i:SI (plus:SI (reg/f:SI 7 sp)
(const_int 4 [0x4])) [2 a+0 S4 A32]))))
(clobber (reg:CC 17 flags))
]) 265 {*mulsidi3_insn} (insn_list:REG_DEP_TRUE 7 (nil))
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil)))
(insn:HI 12 11 17 2 (parallel [
(set (reg:DI 0 ax [62])
(ashiftrt:DI (reg:DI 0 ax [62])
(const_int 15 [0xf])))
(clobber (reg:CC 17 flags))
]) 437 {*ashrdi3_1} (insn_list:REG_DEP_TRUE 11 (nil))
(expr_list:REG_UNUSED (reg:CC 17 flags)
(expr_list:REG_UNUSED (reg:SI 1 dx)
(nil))))
into
(insn:TI 11 31 37 2 (parallel [
(set (reg:DI 0 ax [62])
(mult:DI (sign_extend:DI (reg/v:SI 0 ax [orig:60 b ] [60]))
(sign_extend:DI (mem/c/i:SI (plus:SI (reg/f:SI 7 sp)
(const_int 4 [0x4])) [2 a+0 S4 A32]))))
(clobber (reg:CC 17 flags))
]) 265 {*mulsidi3_insn} (nil)
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil)))
(insn:TI 37 11 38 2 (parallel [
(set (reg:SI 0 ax [62])
(ior:SI (ashiftrt:SI (reg:SI 0 ax [62])
(const_int 15 [0xf]))
(ashift:SI (reg:SI 1 dx [+4 ])
(minus:QI (const_int 32 [0x20])
(const_int 15 [0xf])))))
(clobber (reg:CC 17 flags))
]) 438 {x86_shrd_1} (nil)
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil)))
(insn:TI 38 37 26 2 (parallel [
(set (reg:SI 1 dx [+4 ])
(ashiftrt:SI (reg:SI 1 dx [+4 ])
(const_int 15 [0xf])))
(clobber (reg:CC 17 flags))
]) 443 {*ashrsi3_1} (nil)
(expr_list:REG_UNUSED (reg:CC 17 flags)
(expr_list:REG_UNUSED (reg:SI 1 dx [+4 ])
(nil))))
note the problematic partially dead DI ax:dx which flow does not handle,
so the redundant instruction does not get deleted. A peephole might be
able to fix this until new dataflow maybe handles this case(?).
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu dot
| |org, hubicka at gcc dot gnu
| |dot org
Severity|enhancement |normal
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
GCC host triplet|i486 |
GCC target triplet| |i?86-*-*
Known to fail|4.0.3 4.1.1 |4.0.3 4.1.1 4.2.0
Last reconfirmed|0000-00-00 00:00:00 |2006-10-09 14:58:01
date| |
Summary|[regression] missed- |[4.0/4.1/4.2 Regression]
|optimization (in unneeded |missed-optimization (in
|code elimination) |unneeded code elimination)
Target Milestone|--- |4.0.4
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29401
