On Thu, Jul 6, 2023 at 3:14 AM liuhongt <[email protected]> wrote:
>
> For testcase
>
> void __cond_swap(double* __x, double* __y) {
> bool __r = (*__x < *__y);
> auto __tmp = __r ? *__x : *__y;
> *__y = __r ? *__y : *__x;
> *__x = __tmp;
> }
>
> GCC-14 with -O2 and -march=x86-64 options generates the following code:
>
> __cond_swap(double*, double*):
> movsd xmm1, QWORD PTR [rdi]
> movsd xmm0, QWORD PTR [rsi]
> comisd xmm0, xmm1
> jbe .L2
> movq rax, xmm1
> movapd xmm1, xmm0
> movq xmm0, rax
> .L2:
> movsd QWORD PTR [rsi], xmm1
> movsd QWORD PTR [rdi], xmm0
> ret
>
> rax is used to save and restore DFmode value. In RA both GENERAL_REGS
> and SSE_REGS cost zero since we didn't disparage the
> alternative in movdf_internal pattern, according to register
> allocation order, GENERAL_REGS is allocated. The patch add ? for
> alternative (r,v) and (v,r) just like we did for movsf/hf/bf_internal
> pattern, after that we get optimal RA.
>
> __cond_swap:
> .LFB0:
> .cfi_startproc
> movsd (%rdi), %xmm1
> movsd (%rsi), %xmm0
> comisd %xmm1, %xmm0
> jbe .L2
> movapd %xmm1, %xmm2
> movapd %xmm0, %xmm1
> movapd %xmm2, %xmm0
> .L2:
> movsd %xmm1, (%rsi)
> movsd %xmm0, (%rdi)
> ret
>
> Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}
> Ok for trunk?
>
>
> gcc/ChangeLog:
>
> PR target/110170
> * config/i386/i386.md (movdf_internal): Disparage slightly for
> 2 alternatives (r,v) and (v,r) by adding constraint modifier
> '?'.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/i386/pr110170-3.c: New test.
OK.
Thanks,
Uros.
> ---
> gcc/config/i386/i386.md | 4 ++--
> gcc/testsuite/gcc.target/i386/pr110170-3.c | 11 +++++++++++
> 2 files changed, 13 insertions(+), 2 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/i386/pr110170-3.c
>
> diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
> index a82cc353cfd..e47ced1bb70 100644
> --- a/gcc/config/i386/i386.md
> +++ b/gcc/config/i386/i386.md
> @@ -3915,9 +3915,9 @@ (define_split
> ;; Possible store forwarding (partial memory) stall in alternatives 4, 6 and
> 7.
> (define_insn "*movdf_internal"
> [(set (match_operand:DF 0 "nonimmediate_operand"
> - "=Yf*f,m ,Yf*f,?r ,!o,?*r ,!o,!o,?r,?m,?r,?r,v,v,v,m,*x,*x,*x,m ,r
> ,v,r ,o ,r ,m")
> + "=Yf*f,m ,Yf*f,?r ,!o,?*r ,!o,!o,?r,?m,?r,?r,v,v,v,m,*x,*x,*x,m
> ,?r,?v,r ,o ,r ,m")
> (match_operand:DF 1 "general_operand"
> - "Yf*fm,Yf*f,G ,roF,r ,*roF,*r,F ,rm,rC,C ,F ,C,v,m,v,C ,*x,m ,*x,v,r
> ,roF,rF,rmF,rC"))]
> + "Yf*fm,Yf*f,G ,roF,r ,*roF,*r,F ,rm,rC,C ,F ,C,v,m,v,C ,*x,m ,*x, v,
> r,roF,rF,rmF,rC"))]
> "!(MEM_P (operands[0]) && MEM_P (operands[1]))
> && (lra_in_progress || reload_completed
> || !CONST_DOUBLE_P (operands[1])
> diff --git a/gcc/testsuite/gcc.target/i386/pr110170-3.c
> b/gcc/testsuite/gcc.target/i386/pr110170-3.c
> new file mode 100644
> index 00000000000..70daa89e9aa
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr110170-3.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile { target { ! ia32 } } } */
> +/* { dg-options "-O2 -fno-if-conversion -fno-if-conversion2" } */
> +/* { dg-final { scan-assembler-not {(?n)movq.*r} } } */
> +
> +void __cond_swap(double* __x, double* __y) {
> + _Bool __r = (*__x < *__y);
> + double __tmp = __r ? *__x : *__y;
> + *__y = __r ? *__y : *__x;
> + *__x = __tmp;
> +}
> +
> --
> 2.39.1.388.g2fc9e9ca3c
>
