申威编译器优化指令操作数越界问题

发表于 分类于 本文字数： 3.7k 阅读时长 ≈ 3 分钟

申威上面的编译器问题看来还不少，上一篇文章说到了浮点型优化的问题，今天又遇到指令操作数越界的问题（虽然是个警告，但不排除可能存在其它隐含的问题）。

现象

环境与上篇文章提到的一致，在做申威平台的兼容时，采用嵌入式汇编实现 spinlock 时，开启 -O2 优化遇到了 operand out of range 警告。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
$ gcc -S -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wimplicit-fallthrough=3 -Wcast-function-type -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -Wno-stringop-truncation -O2 -I. -I/mnt/nvme0n1/postgres-14.2/build/../src/backend/replication -I../../../src/include -I/mnt/nvme0n1/postgres-14.2/build/../src/include  -D_GNU_SOURCE   -c -o walreceiverfuncs.s /mnt/nvme0n1/postgres-14.2/build/../src/backend/replication/walreceiverfuncs.c

$ gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wimplicit-fallthrough=3 -Wcast-function-type -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -Wno-stringop-truncation -O2 -I. -I/mnt/nvme0n1/postgres-14.2/build/../src/backend/replication -I../../../src/include -I/mnt/nvme0n1/postgres-14.2/build/../src/include  -D_GNU_SOURCE   -c -o walreceiverfuncs.o walreceiverfuncs.s
walreceiverfuncs.s: Assembler messages:
walreceiverfuncs.s:229: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:233: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:303: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:307: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:396: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:400: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:484: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:488: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:575: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:579: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:759: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:763: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:932: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:936: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:1053: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:1057: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:1159: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)
walreceiverfuncs.s:1163: 警告：operand out of range (0x00000000000008c0 is not between 0xfffffffffffff800 and 0x00000000000007ff)

$ sed -n 229,233p walreceiverfuncs.s
   lldl    $1, 2240($9)
   cmpeq   $1, 0, $2
   wr_f    $2
   mov     $2, $0
   lstl    $0, 2240($9)
   rd_f    $0

从警告信息来看，操作数的取值范围为 [-2048, 2047]，而实际上 lldl $1, 2240($9) 和 lstl $0, 2240($9) 这两个的取值已经超过了这个范围，从而导致警告（我想知道的是为什么是警告，而不是错误）。
程序能正常编译出来，回归测试也能顺利通过，但是这个警告总是让人不放心，为此将这个问题同样地转给了申威的人，希望他们能给出回答。

笑林广记 - 王监生

一监生姓王，加纳知县到任。
初落学，青衿呈书，得牵牛章，讲诵之际，忽问那“王见之”是何人，答曰：“此王诵之之兄也。”
又问那“王曰”然是何人，答曰：“此王曰，叟之弟也。”
曰：“妙得紧。且喜我王氏一门，都在书上。”