target/arm: Fix calculation of LTP mask when LR is 0

In mve_element_mask(), we calculate a mask for tail predication which
should have a number of 1 bits based on the value of LR.  However,
our MAKE_64BIT_MASK() macro has undefined behaviour when passed a
zero length.  Special case this to give the all-zeroes mask we
require.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

diff --git a/target/arm/mve_helper.c b/target/arm/mve_helper.c
index 1a4b2ef..bc67b86 100644 (file)
--- a/target/arm/mve_helper.c
+++ b/target/arm/mve_helper.c
@@ -64,7 +64,8 @@ static uint16_t mve_element_mask(CPUARMState *env)
          */
         int masklen = env->regs[14] << env->v7m.ltpsize;
         assert(masklen <= 16);
-        mask &= MAKE_64BIT_MASK(0, masklen);
+        uint16_t ltpmask = masklen ? MAKE_64BIT_MASK(0, masklen) : 0;
+        mask &= ltpmask;
     }
 
     if ((env->condexec_bits & 0xf) == 0) {