https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127326
--- Comment #9 from Uroš Bizjak <ubizjak at gmail dot com> ---
Whent asm constraint in the testcase is changed to "+rm":
movl 48(%esp), %eax
movl $10, (%esp)
movl $0, 4(%esp)
movl $0, 8(%esp)
movl $809369600, 12(%esp)
<--- **asm is here**
movl (%esp), %esi
movl 4(%esp), %ebx
movl $10, 16(%esp) <-- dead store
movl 8(%esp), %ecx
movl 12(%esp), %edx
movl $0, 20(%esp) <-- dead store
movl %esi, (%eax)
movl %ebx, 4(%eax)
movl %ecx, 8(%eax)
movl %edx, 12(%eax)
movl $0, 24(%esp) <-- dead store
movl $809369600, 28(%esp) <-- dead store
where .reload pass creates:
11: [sp:SI+0x10]=0xa
12: [sp:SI+0x14]=0
13: [sp:SI+0x18]=0
14: [sp:SI+0x1c]=0x303e0000 <--- the constant is already on stack
36: dx:SI=[sp:SI+0x10]
30: [sp:SI]=dx:SI
37: cx:SI=[sp:SI+0x14]
31: [sp:SI+0x4]=cx:SI
38: bx:SI=[sp:SI+0x18]
32: [sp:SI+0x8]=bx:SI
39: si:SI=[sp:SI+0x1c]
33: [sp:SI+0xc]=si:SI <--- another copy of the constant on stack
16: {[sp:SI]=asm_operands;clobber flags:CC;}
6: si:SI=[sp:SI]
7: bx:SI=[sp:SI+0x4]
8: cx:SI=[sp:SI+0x8]
9: dx:SI=[sp:SI+0xc]
17: [ax:SI]=si:SI
18: [ax:SI+0x4]=bx:SI
19: [ax:SI+0x8]=cx:SI
20: [ax:SI+0xc]=dx:SI
and finally, when the constraint is changed to "+m", we get optimal assembly:
movl 32(%esp), %eax
movl $10, (%esp)
movl $0, 4(%esp)
movl $0, 8(%esp)
movl $809369600, 12(%esp)
<--- **asm is here**
movl (%esp), %edx
movl %edx, (%eax)
movl 4(%esp), %edx
movl %edx, 4(%eax)
movl 8(%esp), %edx
movl %edx, 8(%eax)
movl 12(%esp), %edx
movl %edx, 12(%eax)
where .reload pass creates:
6: [sp:SI]=0xa
7: [sp:SI+0x4]=0
8: [sp:SI+0x8]=0
9: [sp:SI+0xc]=0x303e0000
10: {[sp:SI]=asm_operands;clobber flags:CC;}
11: dx:SI=[sp:SI]
REG_EQUIV [frame:SI-0x10]
12: [ax:SI]=dx:SI
13: dx:SI=[sp:SI+0x4]
REG_EQUIV [frame:SI-0xc]
14: [ax:SI+0x4]=dx:SI
15: dx:SI=[sp:SI+0x8]
REG_EQUIV [frame:SI-0x8]
16: [ax:SI+0x8]=dx:SI
17: dx:SI=[sp:SI+0xc]
REG_EQUIV [frame:SI-0x4]
18: [ax:SI+0xc]=dx:SI
