target/arm: Introduce pred_count_test

For WHILE, we have the count of enabled predicates, so we don't
need to search to compute the PredTest result.  Reuse the logic
that will shortly be required for counted predicates.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20250704142112.1018902-71-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/tcg/sve_helper.c

@@ -4102,30 +4102,46 @@ uint64_t HELPER(sve_cntp)(void *vn, void *vg, uint32_t pred_desc)
     return sum;
 }
 
+/* C.f. Arm pseudocode PredCountTest */
+static uint32_t pred_count_test(uint32_t elements, uint32_t count, bool invert)
+{
+    uint32_t flags;
+
+    if (count == 0) {
+        flags = 1;                              /* !N, Z, C */
+    } else if (!invert) {
+        flags = (1u << 31) | 2;                 /* N, !Z */
+        flags |= count != elements;             /* C */
+    } else {
+        flags = 2;                              /* !Z, !C */
+        flags |= (count == elements) << 31;     /* N */
+    }
+    return flags;
+}
+
 uint32_t HELPER(sve_whilel)(void *vd, uint32_t count, uint32_t pred_desc)
 {
     intptr_t oprsz = FIELD_EX32(pred_desc, PREDDESC, OPRSZ);
     intptr_t esz = FIELD_EX32(pred_desc, PREDDESC, ESZ);
     uint64_t esz_mask = pred_esz_masks[esz];
     ARMPredicateReg *d = vd;
-    uint32_t flags;
-    intptr_t i;
+    intptr_t i, oprbits = oprsz * 8;
 
-    /* Begin with a zero predicate register.  */
-    flags = do_zero(d, oprsz);
-    if (count == 0) {
-        return flags;
-    }
+    tcg_debug_assert(count <= oprbits);
 
-    /* Set all of the requested bits.  */
-    for (i = 0; i < count / 64; ++i) {
-        d->p[i] = esz_mask;
-    }
-    if (count & 63) {
-        d->p[i] = MAKE_64BIT_MASK(0, count & 63) & esz_mask;
+    /* Begin with a zero predicate register.  */
+    do_zero(d, oprsz);
+    if (count) {
+        /* Set all of the requested bits.  */
+        for (i = 0; i < count / 64; ++i) {
+            d->p[i] = esz_mask;
+        }
+        if (count & 63) {
+            d->p[i] = MAKE_64BIT_MASK(0, count & 63) & esz_mask;
+        }
     }
 
-    return predtest_ones(d, oprsz, esz_mask);
+    return pred_count_test(oprbits, count, false);
 }
 
 uint32_t HELPER(sve_whileg)(void *vd, uint32_t count, uint32_t pred_desc)
@@ -4134,34 +4150,29 @@ uint32_t HELPER(sve_whileg)(void *vd, uint32_t count, uint32_t pred_desc)
     intptr_t esz = FIELD_EX32(pred_desc, PREDDESC, ESZ);
     uint64_t esz_mask = pred_esz_masks[esz];
     ARMPredicateReg *d = vd;
-    intptr_t i, invcount, oprbits;
+    intptr_t i, invcount, oprbits = oprsz * 8;
     uint64_t bits;
 
-    if (count == 0) {
-        return do_zero(d, oprsz);
-    }
-
-    oprbits = oprsz * 8;
     tcg_debug_assert(count <= oprbits);
 
-    bits = esz_mask;
-    if (oprbits & 63) {
-        bits &= MAKE_64BIT_MASK(0, oprbits & 63);
-    }
-
-    invcount = oprbits - count;
-    for (i = (oprsz - 1) / 8; i > invcount / 64; --i) {
-        d->p[i] = bits;
+    /* Begin with a zero predicate register.  */
+    do_zero(d, oprsz);
+    if (count) {
+        /* Set all of the requested bits.  */
         bits = esz_mask;
-    }
-
-    d->p[i] = bits & MAKE_64BIT_MASK(invcount & 63, 64);
+        if (oprbits & 63) {
+            bits &= MAKE_64BIT_MASK(0, oprbits & 63);
+        }
 
-    while (--i >= 0) {
-        d->p[i] = 0;
+        invcount = oprbits - count;
+        for (i = (oprsz - 1) / 8; i > invcount / 64; --i) {
+            d->p[i] = bits;
+            bits = esz_mask;
+        }
+        d->p[i] = bits & MAKE_64BIT_MASK(invcount & 63, 64);
     }
 
-    return predtest_ones(d, oprsz, esz_mask);
+    return pred_count_test(oprbits, count, true);
 }
 
 /* Recursive reduction on a function;