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[PULL,03/44] target/arm: Fix MVE VSLI by 0 and VSRI by <dt>

Message ID 20210825103534.6936-4-peter.maydell@linaro.org
State New
Headers show
Series [PULL,01/44] target/arm: Note that we handle VMOVL as a special case of VSHLL | expand

Commit Message

Peter Maydell Aug. 25, 2021, 10:34 a.m. UTC 
In the MVE shift-and-insert insns, we special case VSLI by 0
and VSRI by <dt>. VSRI by <dt> means "don't update the destination",
which is what we've implemented. However VSLI by 0 is "set
destination to the input", so we don't want to use the same
special-casing that we do for VSRI by <dt>.

Since the generic logic gives the right answer for a shift
by 0, just use that.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/mve_helper.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)
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Patch

diff --git a/target/arm/mve_helper.c b/target/arm/mve_helper.c
index db5d6220854..f14fa914b68 100644
--- a/target/arm/mve_helper.c
+++ b/target/arm/mve_helper.c
@@ -1279,11 +1279,12 @@  DO_2SHIFT_S(vrshli_s, DO_VRSHLS)
         uint16_t mask;                                                  \
         uint64_t shiftmask;                                             \
         unsigned e;                                                     \
-        if (shift == 0 || shift == ESIZE * 8) {                         \
+        if (shift == ESIZE * 8) {                                       \
             /*                                                          \
-             * Only VSLI can shift by 0; only VSRI can shift by <dt>.   \
-             * The generic logic would give the right answer for 0 but  \
-             * fails for <dt>.                                          \
+             * Only VSRI can shift by <dt>; it should mean "don't       \
+             * update the destination". The generic logic can't handle  \
+             * this because it would try to shift by an out-of-range    \
+             * amount, so special case it here.                         \
              */                                                         \
             goto done;                                                  \
         }                                                               \