https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106594
--- Comment #2 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #1)
> I believe this was some match.pd simplification - why does this affect the
> addressing mode? Is the IVOPTs result different or does it differ later?
The results in IVOpts don't change aside from the changes mentioned above. It
looks like this was previously being matched in RTL through combine.
Before we had
(insn 25 24 26 4 (set (reg:DI 118)
(sign_extend:DI (reg:SI 117))) "/app/example.c":12:35 109
{*extendsidi2_aarch64}
(expr_list:REG_DEAD (reg:SI 117)
(nil)))
(insn 26 25 27 4 (set (reg:SI 119 [ constellation_64qam[_6] ])
(mem/u:SI (plus:DI (mult:DI (reg:DI 118)
(const_int 4 [0x4]))
(reg/f:DI 120)) [1 constellation_64qam[_6]+0 S4 A32]))
"/app/example.c":12:14 52 {*movsi_aarch64}
Trying 25 -> 26:
25: r118:DI=sign_extend(r117:SI)
REG_DEAD r117:SI
26: r119:SI=[r118:DI*0x4+r120:DI]
REG_DEAD r118:DI
REG_EQUAL [r118:DI*0x4+`constellation_64qam']
Successfully matched this instruction:
(set (reg:SI 119 [ constellation_64qamD.3590[_6] ])
(mem/u:SI (plus:DI (mult:DI (sign_extend:DI (reg:SI 117))
(const_int 4 [0x4]))
(reg/f:DI 120)) [1 constellation_64qamD.3590[_6]+0 S4 A32]))
allowing combination of insns 25 and 26
original costs 4 + 16 = 20
replacement cost 16
deferring deletion of insn with uid = 25.
modifying insn i3 26: r119:SI=[sign_extend(r117:SI)*0x4+r120:DI]
REG_DEAD r117:SI
deferring rescan insn with uid = 26.
now, instead we have
(insn 24 23 25 4 (set (reg:DI 116)
(sign_extend:DI (reg:SI 115))) "/app/example.c":12:35 126
{*extendsidi2_aarch64}
(expr_list:REG_DEAD (reg:SI 115)
(nil)))
(insn 25 24 26 4 (set (reg:SI 117 [ constellation_64qam[_5] ])
(mem/u:SI (plus:DI (mult:DI (reg:DI 116)
(const_int 4 [0x4]))
(reg/f:DI 118)) [1 constellation_64qam[_5]+0 S4 A32]))
"/app/example.c":12:14 52 {*movsi_aarch64}
Trying 24 -> 25:
24: r116:DI=sign_extend(r115:SI)
REG_DEAD r115:SI
25: r117:SI=[r116:DI*0x4+r118:DI]
REG_DEAD r116:DI
REG_EQUAL [r116:DI*0x4+`constellation_64qam']
Failed to match this instruction:
(set (reg:SI 117 [ constellation_64qamD.3641[_5] ])
(mem/u:SI (plus:DI (and:DI (mult:DI (subreg:DI (reg:SI 115) 0)
(const_int 4 [0x4]))
(const_int 252 [0xfc]))
(reg/f:DI 118)) [1 constellation_64qamD.3641[_5]+0 S4 A32]))
where the sign extend has suddenly turned into an and.
I don't know why though, the two input RTLs look identical to me.
