On Sat, May 6, 2023 at 4:00 PM Roger Sayle <ro...@nextmovesoftware.com> wrote:
>
>
> Hi Uros,
> This is a repost/respin of a patch that was conditionally approved:
> https://gcc.gnu.org/pipermail/gcc-patches/2023-January/609470.html
>
> This patch adds a convenient post-reload splitter for setting/updating
> the highpart of a TImode variable, using i386's previously added
> split_double_concat infrastructure.
>
> For the new test case below:
>
> __int128 foo(__int128 x, unsigned long long y)
> {
> __int128 t = (__int128)y << 64;
> __int128 r = (x & ~0ull) | t;
> return r;
> }
>
> mainline GCC with -O2 currently generates:
>
> foo: movq %rdi, %rcx
> xorl %eax, %eax
> xorl %edi, %edi
> orq %rcx, %rax
> orq %rdi, %rdx
> ret
>
> with this patch, GCC instead now generates the much better:
>
> foo: movq %rdi, %rcx
> movq %rcx, %rax
> ret
>
> It turns out that the -m32 equivalent of this testcase, already
> avoids using explict orl/xor instructions, as it gets optimized
> (in combine) by a completely different path. Given that this idiom
> isn't seen in 32-bit code (so this pattern doesn't match with -m32),
> and also that the shorter 32-bit AND bitmask is represented as a
> CONST_INT rather than a CONST_WIDE_INT, this new define_insn_and_split
> is implemented for just TARGET_64BIT rather than contort a "generic"
> implementation using DWI mode iterators.
>
> 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 now that we're back in stage 1?
>
>
> 2023-05-06 Roger Sayle <ro...@nextmovesoftware.com>
>
> gcc/ChangeLog
> * config/i386/i386.md (any_or_plus): Move definition earlier.
> (*insvti_highpart_1): New define_insn_and_split to overwrite
> (insv) the highpart of a TImode register/memory.
>
> gcc/testsuite/ChangeLog
> * gcc.target/i386/insvti_highpart-1.c: New test case.
@@ -3479,6 +3479,31 @@
"mov{b}\t{%h1, %h0|%h0, %h1}"
[(set_attr "type" "imov")
(set_attr "mode" "QI")])
+
+(define_code_iterator any_or_plus [plus ior xor])
Please add a line of vertical space here.
+(define_insn_and_split "*insvti_highpart_1"
...
+ && CONST_WIDE_INT_P (operands[3])
+ && CONST_WIDE_INT_NUNITS (operands[3]) == 2
+ && CONST_WIDE_INT_ELT (operands[3], 0) == -1
+ && CONST_WIDE_INT_ELT (operands[3], 1) == 0"
+ "#"
+ "&& reload_completed"
+ [(clobber (const_int 0))]
The above RTX is unreachable, but please use
[(const_int 0)]
as is the case with similar patterns.
OK with the above changes.
Thanks,
Uros.
