On Sun, Jul 9, 2023 at 11:30 PM Roger Sayle <ro...@nextmovesoftware.com> wrote:
>
>
> This patch implements another of Uros' suggestions, to investigate a
> insvti_lowpart_1 pattern to improve TImode parameter passing on x86_64.
> In PR 88873, the RTL the middle-end expands for passing V2DF in TImode
> is subtly different from what it does for V2DI in TImode, sufficiently so
> that my explanations for why insvti_lowpart_1 isn't required don't apply
> in this case.
>
> This patch adds an insvti_lowpart_1 pattern, complementing the existing
> insvti_highpart_1 pattern, and also a 32-bit variant, insvdi_lowpart_1.
> Because the middle-end represents 128-bit constants using CONST_WIDE_INT
> and 64-bit constants using CONST_INT, it's easiest to treat these as
> different patterns, rather than attempt <dwi> parameterization.
>
> This patch also includes a peephole2 (actually a pair) to transform
> xchg instructions into mov instructions, when one of the destinations
> is unused. This optimization is required to produce the optimal code
> sequences below.
>
> For the 64-bit case:
>
> __int128 foo(__int128 x, unsigned long long y)
> {
> __int128 m = ~((__int128)~0ull);
> __int128 t = x & m;
> __int128 r = t | y;
> return r;
> }
>
> Before:
> xchgq %rdi, %rsi
> movq %rdx, %rax
> xorl %esi, %esi
> xorl %edx, %edx
> orq %rsi, %rax
> orq %rdi, %rdx
> ret
>
> After:
> movq %rdx, %rax
> movq %rsi, %rdx
> ret
>
> For the 32-bit case:
>
> long long bar(long long x, int y)
> {
> long long mask = ~0ull << 32;
> long long t = x & mask;
> long long r = t | (unsigned int)y;
> return r;
> }
>
> Before:
> pushl %ebx
> movl 12(%esp), %edx
> xorl %ebx, %ebx
> xorl %eax, %eax
> movl 16(%esp), %ecx
> orl %ebx, %edx
> popl %ebx
> orl %ecx, %eax
> ret
>
> After:
> movl 12(%esp), %eax
> movl 8(%esp), %edx
> ret
>
> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> and make -k check, both with and without --target_board=unix{-m32}
> with no new failures. Ok for mainline?
>
>
> 2023-07-09 Roger Sayle <ro...@nextmovesoftware.com>
>
> gcc/ChangeLog
> * config/i386/i386.md (peephole2): Transform xchg insn with a
> REG_UNUSED note to a (simple) move.
> (*insvti_lowpart_1): New define_insn_and_split.
> (*insvdi_lowpart_1): Likewise.
>
> gcc/testsuite/ChangeLog
> * gcc.target/i386/insvdi_lowpart-1.c: New test case.
> * gcc.target/i386/insvti_lowpart-1.c: Likewise.
OK.
Thanks,
Uros.
>
>
> Cheers,
> Roger
> --
>
