Current GCC generates:


&nbsp;test2:
.LFB0:
&nbsp; &nbsp; &nbsp; &nbsp; .cfi_startproc
&nbsp; &nbsp; &nbsp; &nbsp; xorl &nbsp; &nbsp;%edx, %edx
&nbsp; &nbsp; &nbsp; &nbsp; cmpl &nbsp; &nbsp;$3, (%rdi)
&nbsp; &nbsp; &nbsp; &nbsp; jle &nbsp; &nbsp; .L1
&nbsp; &nbsp; &nbsp; &nbsp; movl &nbsp; &nbsp;16(%rdi), %eax
&nbsp; &nbsp; &nbsp; &nbsp; cmpl &nbsp; &nbsp;$1, %eax
&nbsp; &nbsp; &nbsp; &nbsp; je &nbsp; &nbsp; &nbsp;.L4
&nbsp; &nbsp; &nbsp; &nbsp; subl &nbsp; &nbsp;$2, %eax
&nbsp; &nbsp; &nbsp; &nbsp; cmpl &nbsp; &nbsp;$4, %eax
&nbsp; &nbsp; &nbsp; &nbsp; ja &nbsp; &nbsp; &nbsp;.L1
&nbsp; &nbsp; &nbsp; &nbsp; movl &nbsp; &nbsp;CSWTCH.1(,%rax,4), %edx
.L1:
&nbsp; &nbsp; &nbsp; &nbsp; movl &nbsp; &nbsp;%edx, %eax
&nbsp; &nbsp; &nbsp; &nbsp; ret
&nbsp; &nbsp; &nbsp; &nbsp; .p2align 4,,10
&nbsp; &nbsp; &nbsp; &nbsp; .p2align 3
.L4:
&nbsp; &nbsp; &nbsp; &nbsp; movl &nbsp; &nbsp;$12, %edx
&nbsp; &nbsp; &nbsp; &nbsp; jmp &nbsp; &nbsp; .L1
&nbsp; &nbsp; &nbsp; &nbsp; .cfi_endproc
.LFE0:
&nbsp; &nbsp; &nbsp; &nbsp; .size &nbsp; test2, .-test2
&nbsp; &nbsp; &nbsp; &nbsp; .section &nbsp; &nbsp; &nbsp; &nbsp;.rodata
&nbsp; &nbsp; &nbsp; &nbsp; .align 16
&nbsp; &nbsp; &nbsp; &nbsp; .type &nbsp; CSWTCH.1, @object
&nbsp; &nbsp; &nbsp; &nbsp; .size &nbsp; CSWTCH.1, 20
CSWTCH.1:
&nbsp; &nbsp; &nbsp; &nbsp; .long &nbsp; 27
&nbsp; &nbsp; &nbsp; &nbsp; .long &nbsp; 38
&nbsp; &nbsp; &nbsp; &nbsp; .long &nbsp; 18
&nbsp; &nbsp; &nbsp; &nbsp; .long &nbsp; 58
&nbsp; &nbsp; &nbsp; &nbsp; .long &nbsp; 68




With the patch attatched:


&nbsp;test2:
.LFB0:
&nbsp; &nbsp; &nbsp; &nbsp; .cfi_startproc
&nbsp; &nbsp; &nbsp; &nbsp; xorl &nbsp; &nbsp;%edx, %edx
&nbsp; &nbsp; &nbsp; &nbsp; cmpl &nbsp; &nbsp;$3, (%rdi)
&nbsp; &nbsp; &nbsp; &nbsp; jle &nbsp; &nbsp; .L1
&nbsp; &nbsp; &nbsp; &nbsp; movl &nbsp; &nbsp;16(%rdi), %eax
&nbsp; &nbsp; &nbsp; &nbsp; subl &nbsp; &nbsp;$1, %eax
&nbsp; &nbsp; &nbsp; &nbsp; cmpl &nbsp; &nbsp;$5, %eax
&nbsp; &nbsp; &nbsp; &nbsp; jbe &nbsp; &nbsp; .L6
.L1:
&nbsp; &nbsp; &nbsp; &nbsp; movl &nbsp; &nbsp;%edx, %eax
&nbsp; &nbsp; &nbsp; &nbsp; ret
&nbsp; &nbsp; &nbsp; &nbsp; .p2align 4,,10
&nbsp; &nbsp; &nbsp; &nbsp; .p2align 3
.L6:
&nbsp; &nbsp; &nbsp; &nbsp; movl &nbsp; &nbsp;CSWTCH.1(,%rax,4), %edx
&nbsp; &nbsp; &nbsp; &nbsp; movl &nbsp; &nbsp;%edx, %eax
&nbsp; &nbsp; &nbsp; &nbsp; ret
&nbsp; &nbsp; &nbsp; &nbsp; .cfi_endproc
.LFE0:
&nbsp; &nbsp; &nbsp; &nbsp; .size &nbsp; test2, .-test2
&nbsp; &nbsp; &nbsp; &nbsp; .section &nbsp; &nbsp; &nbsp; &nbsp;.rodata
&nbsp; &nbsp; &nbsp; &nbsp; .align 16
&nbsp; &nbsp; &nbsp; &nbsp; .type &nbsp; CSWTCH.1, @object
&nbsp; &nbsp; &nbsp; &nbsp; .size &nbsp; CSWTCH.1, 24
CSWTCH.1:
&nbsp; &nbsp; &nbsp; &nbsp; .long &nbsp; 12
&nbsp; &nbsp; &nbsp; &nbsp; .long &nbsp; 27
&nbsp; &nbsp; &nbsp; &nbsp; .long &nbsp; 38
&nbsp; &nbsp; &nbsp; &nbsp; .long &nbsp; 18
&nbsp; &nbsp; &nbsp; &nbsp; .long &nbsp; 58
&nbsp; &nbsp; &nbsp; &nbsp; .long &nbsp; 68


Bootstrap and regression tested pass on x86_64-linux-gnu, OK for master?