Hello!
> 2015-11-09 Segher Boessenkool <seg...@kernel.crashing.org>
>
> * gcc/simplify-rtx.c (simplify_truncation): Simplify TRUNCATE
> of AND of [LA]SHIFTRT.
Revision r230164 (the above patch) regressed:
FAIL: gcc.target/alpha/pr42269-1.c scan-assembler-not addl
on alpha-linux-gnu.
The difference starts in combine, where before the patch, we were able
to combine insns:
(insn 7 6 8 2 (set (reg:DI 82)
(lshiftrt:DI (reg:DI 81 [ x ])
(const_int 16 [0x10]))) pr42269-1.c:8 66 {lshrdi3}
(expr_list:REG_DEAD (reg:DI 81 [ x ])
(nil)))
(insn 8 7 11 2 (set (reg:DI 70 [ _2 ])
(sign_extend:DI (subreg:SI (reg:DI 82) 0))) pr42269-1.c:8 2
{*extendsidi2_1}
(expr_list:REG_DEAD (reg:DI 82)
(nil)))
to:
Trying 7 -> 8:
Successfully matched this instruction:
(set (reg:DI 70 [ _2 ])
(zero_extract:DI (reg/v:DI 80 [ x ])
(const_int 16 [0x10])
(const_int 16 [0x10])))
allowing combination of insns 7 and 8
original costs 4 + 4 = 8
replacement cost 4
deferring deletion of insn with uid = 7.
modifying insn i3 8: r70:DI=zero_extract(r80:DI,0x10,0x10)
deferring rescan insn with uid = 8.
After the patch, the combination fails:
Trying 7 -> 8:
Failed to match this instruction:
(set (reg:DI 70 [ _2 ])
(sign_extend:DI (lshiftrt:SI (subreg:SI (reg/v:DI 80 [ x ]) 0)
(const_int 16 [0x10]))))
Uros.
