https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79593
--- Comment #7 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Jakub Jelinek from comment #2)
> That said, the reason why there is fld1 followed by fld %st(0) is that 1.0
> is used multiple times:
This one can be solved with following patch:
--cut here--
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index cfbe0b0..23f2ea0 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -3660,7 +3660,7 @@
(define_split
[(set (match_operand 0 "any_fp_register_operand")
- (match_operand 1 "memory_operand"))]
+ (match_operand 1 "nonimmediate_operand"))]
"reload_completed
&& (GET_MODE (operands[0]) == TFmode
|| GET_MODE (operands[0]) == XFmode
@@ -3672,7 +3672,7 @@
(define_split
[(set (match_operand 0 "any_fp_register_operand")
- (float_extend (match_operand 1 "memory_operand")))]
+ (float_extend (match_operand 1 "nonimmediate_operand")))]
"reload_completed
&& (GET_MODE (operands[0]) == TFmode
|| GET_MODE (operands[0]) == XFmode
--cut here--
This patch allows conversion from (reg->reg) move to (const->reg) when
appropriate constant can be determined from REG_EQUIV/REG_EQUAL note. It also
handles float_extend cases. Patched gcc now generates:
subl $12, %esp
fldz
movl 16(%esp), %eax
movl 20(%esp), %edx
cmpl %edx, (%eax)
jbe .L1
flds global_data
movl 4(%eax), %eax
fld %st(0)
flds global_data+4
fxch %st(3)
fcomip %st(2), %st
fstp %st(1)
ja .L12
movl %eax, (%esp)
flds (%esp)
fsubp %st, %st(2)
.L5:
fdivrp %st, %st(1)
fldz
fxch %st(1)
fcomi %st(1), %st
fcmovb %st(1), %st
fstp %st(1)
fld1
fcomip %st(1), %st
jnb .L6
fstp %st(0)
fld1
.L6:
.L1:
addl $12, %esp
ret
.p2align 4,,10
.p2align 3
.L12:
movl %eax, (%esp)
movl $0, 4(%esp)
fildq (%esp)
fsubrp %st, %st(2)
jmp .L5
