64 lines
3.0 KiB
Diff
64 lines
3.0 KiB
Diff
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From 07dfcad1b3d9ecbf1afe65d3457a6dbcb31f1b94 Mon Sep 17 00:00:00 2001
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From: gubin <gubin_yewu@cmss.chinamobile.com>
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Date: Tue, 17 Dec 2024 14:47:59 +0800
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Subject: [PATCH] target/arm: Fix UMOPA/UMOPS of 16-bit values
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cherry-pick from ea3f5a90f036734522e9af3bffd77e69e9f47355
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The UMOPA/UMOPS instructions are supposed to multiply unsigned 8 or
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16 bit elements and accumulate the products into a 64-bit element.
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In the Arm ARM pseudocode, this is done with the usual
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infinite-precision signed arithmetic. However our implementation
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doesn't quite get it right, because in the DEF_IMOP_64() macro we do:
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sum += (NTYPE)(n >> 0) * (MTYPE)(m >> 0);
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where NTYPE and MTYPE are uint16_t or int16_t. In the uint16_t case,
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the C usual arithmetic conversions mean the values are converted to
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"int" type and the multiply is done as a 32-bit multiply. This means
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that if the inputs are, for example, 0xffff and 0xffff then the
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result is 0xFFFE0001 as an int, which is then promoted to uint64_t
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for the accumulation into sum; this promotion incorrectly sign
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extends the multiply.
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Avoid the incorrect sign extension by casting to int64_t before
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the multiply, so we do the multiply as 64-bit signed arithmetic,
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which is a type large enough that the multiply can never
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overflow into the sign bit.
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(The equivalent 8-bit operations in DEF_IMOP_32() are fine, because
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the 8-bit multiplies can never overflow into the sign bit of a
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32-bit integer.)
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Cc: qemu-stable@nongnu.org
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Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2372
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Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
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Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
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Message-id: 20240722172957.1041231-3-peter.maydell@linaro.org
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Signed-off-by: gubin <gubin_yewu@cmss.chinamobile.com>
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---
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target/arm/tcg/sme_helper.c | 8 ++++----
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1 file changed, 4 insertions(+), 4 deletions(-)
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diff --git a/target/arm/tcg/sme_helper.c b/target/arm/tcg/sme_helper.c
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index 1ee2690ceb..e94b5335e1 100644
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--- a/target/arm/tcg/sme_helper.c
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+++ b/target/arm/tcg/sme_helper.c
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@@ -1134,10 +1134,10 @@ static uint64_t NAME(uint64_t n, uint64_t m, uint64_t a, uint8_t p, bool neg) \
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uint64_t sum = 0; \
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/* Apply P to N as a mask, making the inactive elements 0. */ \
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n &= expand_pred_h(p); \
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- sum += (NTYPE)(n >> 0) * (MTYPE)(m >> 0); \
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- sum += (NTYPE)(n >> 16) * (MTYPE)(m >> 16); \
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- sum += (NTYPE)(n >> 32) * (MTYPE)(m >> 32); \
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- sum += (NTYPE)(n >> 48) * (MTYPE)(m >> 48); \
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+ sum += (int64_t)(NTYPE)(n >> 0) * (MTYPE)(m >> 0); \
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+ sum += (int64_t)(NTYPE)(n >> 16) * (MTYPE)(m >> 16); \
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+ sum += (int64_t)(NTYPE)(n >> 32) * (MTYPE)(m >> 32); \
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+ sum += (int64_t)(NTYPE)(n >> 48) * (MTYPE)(m >> 48); \
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return neg ? a - sum : a + sum; \
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}
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--
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2.41.0.windows.1
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