target/arm: Fix vd == vm overlap in sve_ldff1_z

If vd == vm, copy vm to scratch, so that we can pre-zero
the output and still access the gather indicies.

Cc: qemu-stable@nongnu.org
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1612
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20230504104232.1877774-1-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
(cherry picked from commit a6771f2)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

target/arm/tcg/sve_helper.c

@@ -6727,6 +6727,7 @@ void sve_ldff1_z(CPUARMState *env, void *vd, uint64_t *vg, void *vm,
     intptr_t reg_off;
     SVEHostPage info;
     target_ulong addr, in_page;
+    ARMVectorReg scratch;
 
     /* Skip to the first true predicate.  */
     reg_off = find_next_active(vg, 0, reg_max, esz);
@@ -6736,6 +6737,11 @@ void sve_ldff1_z(CPUARMState *env, void *vd, uint64_t *vg, void *vm,
         return;
     }
 
+    /* Protect against overlap between vd and vm. */
+    if (unlikely(vd == vm)) {
+        vm = memcpy(&scratch, vm, reg_max);
+    }
+
     /*
      * Probe the first element, allowing faults.
      */