i386: Add new insvti_lowpart_1 and insvdi_lowpart_1 patterns.

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

2023-07-10  Roger Sayle  <roger@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.

0 files changed, 0 insertions, 0 deletions