target/arm: Make asimd_imm_const() public

The function asimd_imm_const() in translate-neon.c is an
implementation of the pseudocode AdvSIMDExpandImm(), which we will
also want for MVE.  Move the implementation to translate.c, with a
prototype in translate.h.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210628135835.6690-4-peter.maydell@linaro.org

target/arm/translate-neon.c

@@ -1781,69 +1781,6 @@ DO_FP_2SH(VCVT_UH, gen_helper_gvec_vcvt_uh)
 DO_FP_2SH(VCVT_HS, gen_helper_gvec_vcvt_hs)
 DO_FP_2SH(VCVT_HU, gen_helper_gvec_vcvt_hu)
 
-static uint64_t asimd_imm_const(uint32_t imm, int cmode, int op)
-{
-    /*
-     * Expand the encoded constant.
-     * Note that cmode = 2,3,4,5,6,7,10,11,12,13 imm=0 is UNPREDICTABLE.
-     * We choose to not special-case this and will behave as if a
-     * valid constant encoding of 0 had been given.
-     * cmode = 15 op = 1 must UNDEF; we assume decode has handled that.
-     */
-    switch (cmode) {
-    case 0: case 1:
-        /* no-op */
-        break;
-    case 2: case 3:
-        imm <<= 8;
-        break;
-    case 4: case 5:
-        imm <<= 16;
-        break;
-    case 6: case 7:
-        imm <<= 24;
-        break;
-    case 8: case 9:
-        imm |= imm << 16;
-        break;
-    case 10: case 11:
-        imm = (imm << 8) | (imm << 24);
-        break;
-    case 12:
-        imm = (imm << 8) | 0xff;
-        break;
-    case 13:
-        imm = (imm << 16) | 0xffff;
-        break;
-    case 14:
-        if (op) {
-            /*
-             * This is the only case where the top and bottom 32 bits
-             * of the encoded constant differ.
-             */
-            uint64_t imm64 = 0;
-            int n;
-
-            for (n = 0; n < 8; n++) {
-                if (imm & (1 << n)) {
-                    imm64 |= (0xffULL << (n * 8));
-                }
-            }
-            return imm64;
-        }
-        imm |= (imm << 8) | (imm << 16) | (imm << 24);
-        break;
-    case 15:
-        imm = ((imm & 0x80) << 24) | ((imm & 0x3f) << 19)
-            | ((imm & 0x40) ? (0x1f << 25) : (1 << 30));
-        break;
-    }
-    if (op) {
-        imm = ~imm;
-    }
-    return dup_const(MO_32, imm);
-}
-
 static bool do_1reg_imm(DisasContext *s, arg_1reg_imm *a,
                         GVecGen2iFn *fn)
 {

target/arm/translate.c

@@ -90,6 +90,63 @@ void arm_translate_init(void)
     a64_translate_init();
 }
 
+uint64_t asimd_imm_const(uint32_t imm, int cmode, int op)
+{
+    /* Expand the encoded constant as per AdvSIMDExpandImm pseudocode */
+    switch (cmode) {
+    case 0: case 1:
+        /* no-op */
+        break;
+    case 2: case 3:
+        imm <<= 8;
+        break;
+    case 4: case 5:
+        imm <<= 16;
+        break;
+    case 6: case 7:
+        imm <<= 24;
+        break;
+    case 8: case 9:
+        imm |= imm << 16;
+        break;
+    case 10: case 11:
+        imm = (imm << 8) | (imm << 24);
+        break;
+    case 12:
+        imm = (imm << 8) | 0xff;
+        break;
+    case 13:
+        imm = (imm << 16) | 0xffff;
+        break;
+    case 14:
+        if (op) {
+            /*
+             * This is the only case where the top and bottom 32 bits
+             * of the encoded constant differ.
+             */
+            uint64_t imm64 = 0;
+            int n;
+
+            for (n = 0; n < 8; n++) {
+                if (imm & (1 << n)) {
+                    imm64 |= (0xffULL << (n * 8));
+                }
+            }
+            return imm64;
+        }
+        imm |= (imm << 8) | (imm << 16) | (imm << 24);
+        break;
+    case 15:
+        imm = ((imm & 0x80) << 24) | ((imm & 0x3f) << 19)
+            | ((imm & 0x40) ? (0x1f << 25) : (1 << 30));
+        break;
+    }
+    if (op) {
+        imm = ~imm;
+    }
+    return dup_const(MO_32, imm);
+}
+
 /* Generate a label used for skipping this instruction */
 void arm_gen_condlabel(DisasContext *s)
 {

target/arm/translate.h

@@ -532,4 +532,20 @@ static inline MemOp finalize_memop(DisasContext *s, MemOp opc)
     return opc | s->be_data;
 }
 
+/**
+ * asimd_imm_const: Expand an encoded SIMD constant value
+ *
+ * Expand a SIMD constant value. This is essentially the pseudocode
+ * AdvSIMDExpandImm, except that we also perform the boolean NOT needed for
+ * VMVN and VBIC (when cmode < 14 && op == 1).
+ *
+ * The combination cmode == 15 op == 1 is a reserved encoding for AArch32;
+ * callers must catch this.
+ *
+ * cmode = 2,3,4,5,6,7,10,11,12,13 imm=0 was UNPREDICTABLE in v7A but
+ * is either not unpredictable or merely CONSTRAINED UNPREDICTABLE in v8A;
+ * we produce an immediate constant value of 0 in these cases.
+ */
+uint64_t asimd_imm_const(uint32_t imm, int cmode, int op);
+
 #endif /* TARGET_ARM_TRANSLATE_H */