On Tue, Apr 29, 2025 at 5:52 PM Uros Bizjak <ubiz...@gmail.com> wrote:
>
> MOVS instructions allow segment override of their source operand, e.g.:
>
> rep movsq %gs:(%rsi), (%rdi)
>
> where %rsi is the address of the source location (with %gs segment override)
> and %rdi is the address of the destination location.
Please be aware that 0x67 prefix (used by x32) is applied before segment
register. That is in
rep movsq %gs:(%esi), (%edi)
the address is %gs + %esi.
> The testcase improves from (-O2 -mno-sse -mtune=generic):
>
> xorl %eax, %eax
> .L2:
> movl %eax, %edx
> addl $8, %eax
> movq %gs:m(%rdx), %rcx
> movq %rcx, (%rdi,%rdx)
> cmpl $240, %eax
> jb .L2
> ret
>
> to:
> movl $m, %esi
> movl $30, %ecx
> rep movsq %gs:(%rsi), (%rdi)
> ret
>
> PR 111657
>
> gcc/ChangeLog:
>
> * config/i386/i386-expand.cc (alg_usable_p): Remove have_as bool
> argument and add dst_as and src_as address space arguments. Reject
> libcall algorithm with dst_as and src_as in the non-default address
> spaces. Reject rep_prefix_{1,4,8}_byte algorithms with dst_as in
> the non-default address space.
> (decide_alg): Remove have_as bool argument and add dst_as and src_as
> address space arguments. Update calls to alg_usable_p.
> (ix86_expand_set_or_cpymem): Update call to decide_alg.
> * config/i386/i386.md (strmov): Do not fail if operand[3] (source)
> is in the non-default address space. Expand with gen_strmov_singleop
> only when operand[1] (destination) is in the default address space.
> (*strmovdi_rex_1): Determine memory operands from insn pattern.
> Allow only when destination is in the default address space.
> Rewrite asm template to use explicit operands.
> (*strmovsi_1): Ditto.
> (*strmovhi_1): DItto.
> (*strmovqi_1): Ditto.
> (*rep_movdi_rex64): Ditto.
> (*rep_movsi): Ditto.
> (*rep_movqi): Ditto.
> (*strsetdi_rex_1): Determine memory operands from insn pattern.
> Allow only when destination is in the default address space.
> (*strsetsi_1): Ditto.
> (*strsethi_1): Ditto.
> (*strsetqi_1): Ditto.
> (*rep_stosdi_rex64): Ditto.
> (*rep_stossi): Ditto.
> (*rep_stosqi): Ditto.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/i386/pr111657-1.c: New test.
>
> Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.
>
> Uros.
--
H.J.
