target-ppc: fix rlwimi, rlwinm, rlwnm for Clang-9

Starting with Clang v9, -Wtype-limits is implemented and triggers a
few "result of comparison is always true" errors when compiling PPC32
targets.

The comparisons seem to be necessary only on PPC64, since the
else branch in PPC32 only has a "g_assert_not_reached();" in all cases.

This patch restructures the code so that the actual if/else is done on a
local flag variable, that is set accordingly for PPC64, and always
true for PPC32.

Signed-off-by: Daniele Buono <dbuono@linux.vnet.ibm.com>
Message-Id: <20200505183818.32688-2-dbuono@linux.vnet.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

target/ppc/translate.c

@@ -1882,6 +1882,7 @@ static void gen_rlwimi(DisasContext *ctx)
         tcg_gen_deposit_tl(t_ra, t_ra, t_rs, sh, me - mb + 1);
     } else {
         target_ulong mask;
+        bool mask_in_32b = true;
         TCGv t1;
 
 #if defined(TARGET_PPC64)
@@ -1890,8 +1891,13 @@ static void gen_rlwimi(DisasContext *ctx)
 #endif
         mask = MASK(mb, me);
 
+#if defined(TARGET_PPC64)
+        if (mask > 0xffffffffu) {
+            mask_in_32b = false;
+        }
+#endif
         t1 = tcg_temp_new();
-        if (mask <= 0xffffffffu) {
+        if (mask_in_32b) {
             TCGv_i32 t0 = tcg_temp_new_i32();
             tcg_gen_trunc_tl_i32(t0, t_rs);
             tcg_gen_rotli_i32(t0, t0, sh);
@@ -1933,12 +1939,18 @@ static void gen_rlwinm(DisasContext *ctx)
         tcg_gen_extract_tl(t_ra, t_rs, rsh, len);
     } else {
         target_ulong mask;
+        bool mask_in_32b = true;
 #if defined(TARGET_PPC64)
         mb += 32;
         me += 32;
 #endif
         mask = MASK(mb, me);
-        if (mask <= 0xffffffffu) {
+#if defined(TARGET_PPC64)
+        if (mask > 0xffffffffu) {
+            mask_in_32b = false;
+        }
+#endif
+        if (mask_in_32b) {
             if (sh == 0) {
                 tcg_gen_andi_tl(t_ra, t_rs, mask);
             } else {
@@ -1973,14 +1985,20 @@ static void gen_rlwnm(DisasContext *ctx)
     uint32_t mb = MB(ctx->opcode);
     uint32_t me = ME(ctx->opcode);
     target_ulong mask;
+    bool mask_in_32b = true;
 
 #if defined(TARGET_PPC64)
     mb += 32;
     me += 32;
 #endif
     mask = MASK(mb, me);
 
-    if (mask <= 0xffffffffu) {
+#if defined(TARGET_PPC64)
+    if (mask > 0xffffffffu) {
+        mask_in_32b = false;
+    }
+#endif
+    if (mask_in_32b) {
         TCGv_i32 t0 = tcg_temp_new_i32();
         TCGv_i32 t1 = tcg_temp_new_i32();
         tcg_gen_trunc_tl_i32(t0, t_rb);