This patch resolves PR target/110104, a missed optimization on x86 around
adc with memory operands.  In i386.md, there's a peephole2 after the
pattern for *add<mode>3_cc_overflow_1 that converts the sequence
reg = add(reg,mem); mem = reg [where the reg is dead afterwards] into
the equivalent mem = add(mem,reg).  The equivalent peephole2 for adc
is missing (after addcarry<mode>), and is added by this patch.

For the example code provided in the bugzilla PR:

Before:
        movq    %rsi, %rax
        mulq    %rdx
        addq    %rax, (%rdi)
        movq    %rdx, %rax
        adcq    8(%rdi), %rax
        adcq    $0, 16(%rdi)
        movq    %rax, 8(%rdi)
        ret

After:
        movq    %rsi, %rax
        mulq    %rdx
        addq    %rax, (%rdi)
        adcq    %rdx, 8(%rdi)
        adcq    $0, 16(%rdi)
        ret

Note that the addq in this example has been transformed by the
existing peephole2 described above.

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?


2023-06-07  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
        PR target/110104
        * config/i386/i386.md (define_peephole2): Transform reg=adc(reg,mem)
        followed by mem=reg into mem=adc(mem,reg) when applicable.

gcc/testsuite/ChangeLog
        PR target/110104
        * gcc.target/i386/pr110104.c: New test case.


Thanks in advance,
Roger
--