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88 lines
3.3 KiB
88 lines
3.3 KiB
commit ba1c3f23d9ba63c38333116eec6043c471c378c4 |
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Author: Noah Goldstein <goldstein.w.n@gmail.com> |
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Date: Wed Jun 15 10:41:28 2022 -0700 |
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x86: Cleanup bounds checking in large memcpy case |
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1. Fix incorrect lower-bound threshold in L(large_memcpy_2x). |
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Previously was using `__x86_rep_movsb_threshold` and should |
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have been using `__x86_shared_non_temporal_threshold`. |
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2. Avoid reloading __x86_shared_non_temporal_threshold before |
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the L(large_memcpy_4x) bounds check. |
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3. Document the second bounds check for L(large_memcpy_4x) |
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more clearly. |
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(cherry picked from commit 89a25c6f64746732b87eaf433af0964b564d4a92) |
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diff --git a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S |
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index 7b27cbdda5fb99f7..618d46d8ce28828c 100644 |
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--- a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S |
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+++ b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S |
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@@ -118,7 +118,13 @@ |
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# define LARGE_LOAD_SIZE (VEC_SIZE * 4) |
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#endif |
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-/* Amount to shift rdx by to compare for memcpy_large_4x. */ |
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+/* Amount to shift __x86_shared_non_temporal_threshold by for |
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+ bound for memcpy_large_4x. This is essentially use to to |
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+ indicate that the copy is far beyond the scope of L3 |
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+ (assuming no user config x86_non_temporal_threshold) and to |
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+ use a more aggressively unrolled loop. NB: before |
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+ increasing the value also update initialization of |
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+ x86_non_temporal_threshold. */ |
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#ifndef LOG_4X_MEMCPY_THRESH |
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# define LOG_4X_MEMCPY_THRESH 4 |
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#endif |
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@@ -724,9 +730,14 @@ L(skip_short_movsb_check): |
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.p2align 4,, 10 |
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#if (defined USE_MULTIARCH || VEC_SIZE == 16) && IS_IN (libc) |
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L(large_memcpy_2x_check): |
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- cmp __x86_rep_movsb_threshold(%rip), %RDX_LP |
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- jb L(more_8x_vec_check) |
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+ /* Entry from L(large_memcpy_2x) has a redundant load of |
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+ __x86_shared_non_temporal_threshold(%rip). L(large_memcpy_2x) |
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+ is only use for the non-erms memmove which is generally less |
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+ common. */ |
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L(large_memcpy_2x): |
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+ mov __x86_shared_non_temporal_threshold(%rip), %R11_LP |
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+ cmp %R11_LP, %RDX_LP |
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+ jb L(more_8x_vec_check) |
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/* To reach this point it is impossible for dst > src and |
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overlap. Remaining to check is src > dst and overlap. rcx |
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already contains dst - src. Negate rcx to get src - dst. If |
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@@ -774,18 +785,21 @@ L(large_memcpy_2x): |
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/* ecx contains -(dst - src). not ecx will return dst - src - 1 |
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which works for testing aliasing. */ |
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notl %ecx |
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+ movq %rdx, %r10 |
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testl $(PAGE_SIZE - VEC_SIZE * 8), %ecx |
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jz L(large_memcpy_4x) |
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- movq %rdx, %r10 |
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- shrq $LOG_4X_MEMCPY_THRESH, %r10 |
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- cmp __x86_shared_non_temporal_threshold(%rip), %r10 |
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+ /* r11 has __x86_shared_non_temporal_threshold. Shift it left |
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+ by LOG_4X_MEMCPY_THRESH to get L(large_memcpy_4x) threshold. |
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+ */ |
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+ shlq $LOG_4X_MEMCPY_THRESH, %r11 |
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+ cmp %r11, %rdx |
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jae L(large_memcpy_4x) |
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/* edx will store remainder size for copying tail. */ |
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andl $(PAGE_SIZE * 2 - 1), %edx |
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/* r10 stores outer loop counter. */ |
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- shrq $((LOG_PAGE_SIZE + 1) - LOG_4X_MEMCPY_THRESH), %r10 |
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+ shrq $(LOG_PAGE_SIZE + 1), %r10 |
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/* Copy 4x VEC at a time from 2 pages. */ |
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.p2align 4 |
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L(loop_large_memcpy_2x_outer): |
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@@ -850,7 +864,6 @@ L(large_memcpy_2x_end): |
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.p2align 4 |
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L(large_memcpy_4x): |
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- movq %rdx, %r10 |
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/* edx will store remainder size for copying tail. */ |
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andl $(PAGE_SIZE * 4 - 1), %edx |
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/* r10 stores outer loop counter. */
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