On Wed, Jun 7, 2023 at 1:05 AM Roger Sayle <ro...@nextmovesoftware.com> wrote:
>
>
> This patch addresses the last remaining issue with PR target/31985, that
> GCC could make better use of memory addressing modes when implementing
> double word addition. This is achieved by adding a define_insn_and_split
> that combines an *add<dwi>3_doubleword with a *concat<mode><dwi>3, so
> that the components of the concat can be used directly, without first
> being loaded into a double word register.
>
> For test_c in the bugzilla PR:
>
> Before:
> pushl %ebx
> subl $16, %esp
> movl 28(%esp), %eax
> movl 36(%esp), %ecx
> movl 32(%esp), %ebx
> movl 24(%esp), %edx
> addl %ecx, %eax
> adcl %ebx, %edx
> movl %eax, 8(%esp)
> movl %edx, 12(%esp)
> addl $16, %esp
> popl %ebx
> ret
>
> After:
> test_c:
> subl $20, %esp
> movl 36(%esp), %eax
> movl 32(%esp), %edx
> addl 28(%esp), %eax
> adcl 24(%esp), %edx
> movl %eax, 8(%esp)
> movl %edx, 12(%esp)
> addl $20, %esp
> ret
>
>
> If this approach is considered acceptable, similar splitters can be
> used for other doubleword operations.
Yes, the approach looks good to me. But please take care not to
interfere with STV transformations.
> 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 <ro...@nextmovesoftware.com>
>
> gcc/ChangeLog
> PR target/31985
> * config/i386/i386.md (*add<dwi>3_doubleword_concat): New
> define_insn_and_split combine *add<dwi>3_doubleword with a
> *concat<mode><dwi>3 for more efficient lowering after reload.
>
> gcc/testsuite/ChangeLog
> PR target/31985
> * gcc.target/i386/pr31985.c: New test case.
OK.
Thanks,
Uros.
>
>
> Roger
> --
>
