https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87678
Uroš Bizjak <ubizjak at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2018-10-22
CC| |segher at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #1 from Uroš Bizjak <ubizjak at gmail dot com> ---
This is due to combine, which only tries to propagate REG_EQUAL to the user.
Consider this slightly simpler test:
--cut here--
float
foo (float x, float y)
{
float z = x + y;
return z * 2.387f;
}
--cut here--
gcc -O2 -m32 -fpic -mfpmath=sse -msse:
movss .LC0@GOTOFF(%eax), %xmm1
mulss %xmm1, %xmm0
Where combine tries to combine:
(insn 8 7 9 2 (set (reg:SF 89)
(mem/u/c:SF (plus:SI (reg:SI 82)
(const:SI (unspec:SI [
(symbol_ref/u:SI ("*.LC0") [flags 0x2])
] UNSPEC_GOTOFF))) [0 S4 A32])) "pic.c":5:12 112
{*movsf_internal}
(expr_list:REG_DEAD (reg:SI 82)
(expr_list:REG_EQUAL (const_double:SF 2.38700008392333984375e+0
[0x0.98c49cp+2])
(nil))))
(insn 9 8 14 2 (set (reg:SF 87)
(mult:SF (reg:SF 88 [ z ])
(reg:SF 89))) "pic.c":5:12 815 {*fop_sf_comm}
(expr_list:REG_DEAD (reg:SF 89)
(expr_list:REG_DEAD (reg:SF 88 [ z ])
(nil))))
Trying 8 -> 9:
8: r89:SF=[r82:SI+const(unspec[`*.LC0'] 1)]
REG_DEAD r82:SI
REG_EQUAL 2.38700008392333984375e+0
9: r87:SF=r88:SF*r89:SF
REG_DEAD r89:SF
REG_DEAD r88:SF
Failed to match this instruction:
(set (reg:SF 87)
(mult:SF (reg:SF 88 [ z ])
(const_double:SF 2.38700008392333984375e+0 [0x0.98c49cp+2])))
Combine should retry with the original source insn.
