https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66822
--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> ---
X86_TUNE_USE_BT also reduces code size:
[hjl@gnu-tools-1 pr66822]$ cat y.i
void bar (void);
void
foo (int x)
{
if (x != 2 && x != 3 && x != 10 && x != 11 && x != 17 && x != 18 && x != 23)
bar ();
}
[hjl@gnu-tools-1 pr66822]$ make y.o
/export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -O2 -m32 -miamcu -mtune=iamcu
-S -o y.s y.i
/export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -O2 -m32 -miamcu -mtune=iamcu
-c -o y.o y.s
rm y.s
[hjl@gnu-tools-1 pr66822]$ objdump -dwr y.o
y.o: file format elf32-i386
Disassembly of section .text:
00000000 <foo>:
0: 83 f8 17 cmp $0x17,%eax
3: 76 0b jbe 10 <foo+0x10>
5: e9 fc ff ff ff jmp 6 <foo+0x6> 6: R_386_PC32 bar
a: 8d b6 00 00 00 00 lea 0x0(%esi),%esi
10: ba 0c 0c 86 00 mov $0x860c0c,%edx
15: 88 c1 mov %al,%cl
17: d3 ea shr %cl,%edx
19: 83 e2 01 and $0x1,%edx
1c: 74 e7 je 5 <foo+0x5>
1e: c3 ret
[hjl@gnu-tools-1 pr66822]$ /export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -O2 -m32 -miamcu -mtune=iamcu
-c y.i -mtune-ctrl=use_bt
[hjl@gnu-tools-1 pr66822]$ objdump -dwr y.o
y.o: file format elf32-i386
Disassembly of section .text:
00000000 <foo>:
0: 83 f8 17 cmp $0x17,%eax
3: 76 0b jbe 10 <foo+0x10>
5: e9 fc ff ff ff jmp 6 <foo+0x6> 6: R_386_PC32 bar
a: 8d b6 00 00 00 00 lea 0x0(%esi),%esi
10: ba 0c 0c 86 00 mov $0x860c0c,%edx
15: 0f a3 c2 bt %eax,%edx
18: 73 eb jae 5 <foo+0x5>
1a: c3 ret
[hjl@gnu-tools-1 pr66822]$
