target/i386: Introduce REX_PREFIX

The existing flag, x86_64_hregs, does not accurately describe
its setting.  It is true if and only if a REX prefix has been
seen.  Yes, that affects the "h" regs, but that's secondary.

Add PREFIX_REX and include this bit in s->prefix.  Add REX_PREFIX
so that the check folds away when x86_64 is compiled out.

Fold away the reg >= 8 check, because bit 3 of the register
number comes from the REX prefix in the first place.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210514151342.384376-16-richard.henderson@linaro.org>

1 files changed, 11 insertions, 18 deletions

diff --git a/target/i386/tcg/translate.c b/target/i386/tcg/translate.c
index 7d7ab3e03d..79a37fb1a7 100644
--- a/target/i386/tcg/translate.c
+++ b/target/i386/tcg/translate.c
@@ -39,6 +39,7 @@
 #define PREFIX_DATA   0x08
 #define PREFIX_ADR    0x10
 #define PREFIX_VEX    0x20
+#define PREFIX_REX    0x40
 
 #ifdef TARGET_X86_64
 #define REX_X(s) ((s)->rex_x)
@@ -105,9 +106,6 @@ typedef struct DisasContext {
     int vex_v;  /* vex vvvv register, without 1's complement.  */
     CCOp cc_op;  /* current CC operation */
     bool cc_op_dirty;
-#ifdef TARGET_X86_64
-    bool x86_64_hregs;
-#endif
     int f_st;   /* currently unused */
     int tf;     /* TF cpu flag */
     int jmp_opt; /* use direct block chaining for direct jumps */
@@ -173,6 +171,12 @@ typedef struct DisasContext {
 #define LMA(S)    (((S)->flags & HF_LMA_MASK) != 0)
 #endif
 
+#ifdef TARGET_X86_64
+#define REX_PREFIX(S)  (((S)->prefix & PREFIX_REX) != 0)
+#else
+#define REX_PREFIX(S)  false
+#endif
+
 static void gen_eob(DisasContext *s);
 static void gen_jr(DisasContext *s, TCGv dest);
 static void gen_jmp(DisasContext *s, target_ulong eip);
@@ -336,14 +340,10 @@ static void gen_update_cc_op(DisasContext *s)
  */
 static inline bool byte_reg_is_xH(DisasContext *s, int reg)
 {
-    if (reg < 4) {
-        return false;
-    }
-#ifdef TARGET_X86_64
-    if (reg >= 8 || s->x86_64_hregs) {
+    /* Any time the REX prefix is present, byte registers are uniform */
+    if (reg < 4 || REX_PREFIX(s)) {
         return false;
     }
-#endif
     return true;
 }
 
@@ -4559,7 +4559,6 @@ static target_ulong disas_insn(DisasContext *s, CPUState *cpu)
 #ifdef TARGET_X86_64
     s->rex_x = 0;
     s->rex_b = 0;
-    s->x86_64_hregs = false;
 #endif
     s->rip_offset = 0; /* for relative ip address */
     s->vex_l = 0;
@@ -4614,12 +4613,11 @@ static target_ulong disas_insn(DisasContext *s, CPUState *cpu)
     case 0x40 ... 0x4f:
         if (CODE64(s)) {
             /* REX prefix */
+            prefixes |= PREFIX_REX;
             rex_w = (b >> 3) & 1;
             rex_r = (b & 0x4) << 1;
             s->rex_x = (b & 0x2) << 2;
             REX_B(s) = (b & 0x1) << 3;
-            /* select uniform byte register addressing */
-            s->x86_64_hregs = true;
             goto next_byte;
         }
         break;
@@ -4643,14 +4641,9 @@ static target_ulong disas_insn(DisasContext *s, CPUState *cpu)
 
             /* 4.1.1-4.1.3: No preceding lock, 66, f2, f3, or rex prefixes. */
             if (prefixes & (PREFIX_REPZ | PREFIX_REPNZ
-                            | PREFIX_LOCK | PREFIX_DATA)) {
+                            | PREFIX_LOCK | PREFIX_DATA | PREFIX_REX)) {
                 goto illegal_op;
             }
-#ifdef TARGET_X86_64
-            if (s->x86_64_hregs) {
-                goto illegal_op;
-            }
-#endif
             rex_r = (~vex2 >> 4) & 8;
             if (b == 0xc5) {
                 /* 2-byte VEX prefix: RVVVVlpp, implied 0f leading opcode byte */