diff --git a/tcg/optimize.c b/tcg/optimize.c
index c239c3bd07..148e360fc6 100644
--- a/tcg/optimize.c
+++ b/tcg/optimize.c
@@ -41,7 +41,7 @@ typedef struct TempOptInfo {
     TCGTemp *prev_copy;
     TCGTemp *next_copy;
     uint64_t val;
-    uint64_t mask;
+    uint64_t z_mask;  /* mask bit is 0 if and only if value bit is 0 */
 } TempOptInfo;
 
 static inline TempOptInfo *ts_info(TCGTemp *ts)
@@ -81,7 +81,7 @@ static void reset_ts(TCGTemp *ts)
     ti->next_copy = ts;
     ti->prev_copy = ts;
     ti->is_const = false;
-    ti->mask = -1;
+    ti->z_mask = -1;
 }
 
 static void reset_temp(TCGArg arg)
@@ -111,14 +111,14 @@ static void init_ts_info(TCGTempSet *temps_used, TCGTemp *ts)
     if (ts->kind == TEMP_CONST) {
         ti->is_const = true;
         ti->val = ts->val;
-        ti->mask = ts->val;
+        ti->z_mask = ts->val;
         if (TCG_TARGET_REG_BITS > 32 && ts->type == TCG_TYPE_I32) {
             /* High bits of a 32-bit quantity are garbage.  */
-            ti->mask |= ~0xffffffffull;
+            ti->z_mask |= ~0xffffffffull;
         }
     } else {
         ti->is_const = false;
-        ti->mask = -1;
+        ti->z_mask = -1;
     }
 }
 
@@ -186,7 +186,7 @@ static void tcg_opt_gen_mov(TCGContext *s, TCGOp *op, TCGArg dst, TCGArg src)
     const TCGOpDef *def;
     TempOptInfo *di;
     TempOptInfo *si;
-    uint64_t mask;
+    uint64_t z_mask;
     TCGOpcode new_op;
 
     if (ts_are_copies(dst_ts, src_ts)) {
@@ -210,12 +210,12 @@ static void tcg_opt_gen_mov(TCGContext *s, TCGOp *op, TCGArg dst, TCGArg src)
     op->args[0] = dst;
     op->args[1] = src;
 
-    mask = si->mask;
+    z_mask = si->z_mask;
     if (TCG_TARGET_REG_BITS > 32 && new_op == INDEX_op_mov_i32) {
         /* High bits of the destination are now garbage.  */
-        mask |= ~0xffffffffull;
+        z_mask |= ~0xffffffffull;
     }
-    di->mask = mask;
+    di->z_mask = z_mask;
 
     if (src_ts->type == dst_ts->type) {
         TempOptInfo *ni = ts_info(si->next_copy);
@@ -621,7 +621,7 @@ void tcg_optimize(TCGContext *s)
     }
 
     QTAILQ_FOREACH_SAFE(op, &s->ops, link, op_next) {
-        uint64_t mask, partmask, affected, tmp;
+        uint64_t z_mask, partmask, affected, tmp;
         int nb_oargs, nb_iargs;
         TCGOpcode opc = op->opc;
         const TCGOpDef *def = &tcg_op_defs[opc];
@@ -855,170 +855,172 @@ void tcg_optimize(TCGContext *s)
 
         /* Simplify using known-zero bits. Currently only ops with a single
            output argument is supported. */
-        mask = -1;
+        z_mask = -1;
         affected = -1;
         switch (opc) {
         CASE_OP_32_64(ext8s):
-            if ((arg_info(op->args[1])->mask & 0x80) != 0) {
+            if ((arg_info(op->args[1])->z_mask & 0x80) != 0) {
                 break;
             }
             QEMU_FALLTHROUGH;
         CASE_OP_32_64(ext8u):
-            mask = 0xff;
+            z_mask = 0xff;
             goto and_const;
         CASE_OP_32_64(ext16s):
-            if ((arg_info(op->args[1])->mask & 0x8000) != 0) {
+            if ((arg_info(op->args[1])->z_mask & 0x8000) != 0) {
                 break;
             }
             QEMU_FALLTHROUGH;
         CASE_OP_32_64(ext16u):
-            mask = 0xffff;
+            z_mask = 0xffff;
             goto and_const;
         case INDEX_op_ext32s_i64:
-            if ((arg_info(op->args[1])->mask & 0x80000000) != 0) {
+            if ((arg_info(op->args[1])->z_mask & 0x80000000) != 0) {
                 break;
             }
             QEMU_FALLTHROUGH;
         case INDEX_op_ext32u_i64:
-            mask = 0xffffffffU;
+            z_mask = 0xffffffffU;
             goto and_const;
 
         CASE_OP_32_64(and):
-            mask = arg_info(op->args[2])->mask;
+            z_mask = arg_info(op->args[2])->z_mask;
             if (arg_is_const(op->args[2])) {
         and_const:
-                affected = arg_info(op->args[1])->mask & ~mask;
+                affected = arg_info(op->args[1])->z_mask & ~z_mask;
             }
-            mask = arg_info(op->args[1])->mask & mask;
+            z_mask = arg_info(op->args[1])->z_mask & z_mask;
             break;
 
         case INDEX_op_ext_i32_i64:
-            if ((arg_info(op->args[1])->mask & 0x80000000) != 0) {
+            if ((arg_info(op->args[1])->z_mask & 0x80000000) != 0) {
                 break;
             }
             QEMU_FALLTHROUGH;
         case INDEX_op_extu_i32_i64:
             /* We do not compute affected as it is a size changing op.  */
-            mask = (uint32_t)arg_info(op->args[1])->mask;
+            z_mask = (uint32_t)arg_info(op->args[1])->z_mask;
             break;
 
         CASE_OP_32_64(andc):
             /* Known-zeros does not imply known-ones.  Therefore unless
                op->args[2] is constant, we can't infer anything from it.  */
             if (arg_is_const(op->args[2])) {
-                mask = ~arg_info(op->args[2])->mask;
+                z_mask = ~arg_info(op->args[2])->z_mask;
                 goto and_const;
             }
             /* But we certainly know nothing outside args[1] may be set. */
-            mask = arg_info(op->args[1])->mask;
+            z_mask = arg_info(op->args[1])->z_mask;
             break;
 
         case INDEX_op_sar_i32:
             if (arg_is_const(op->args[2])) {
                 tmp = arg_info(op->args[2])->val & 31;
-                mask = (int32_t)arg_info(op->args[1])->mask >> tmp;
+                z_mask = (int32_t)arg_info(op->args[1])->z_mask >> tmp;
             }
             break;
         case INDEX_op_sar_i64:
             if (arg_is_const(op->args[2])) {
                 tmp = arg_info(op->args[2])->val & 63;
-                mask = (int64_t)arg_info(op->args[1])->mask >> tmp;
+                z_mask = (int64_t)arg_info(op->args[1])->z_mask >> tmp;
             }
             break;
 
         case INDEX_op_shr_i32:
             if (arg_is_const(op->args[2])) {
                 tmp = arg_info(op->args[2])->val & 31;
-                mask = (uint32_t)arg_info(op->args[1])->mask >> tmp;
+                z_mask = (uint32_t)arg_info(op->args[1])->z_mask >> tmp;
             }
             break;
         case INDEX_op_shr_i64:
             if (arg_is_const(op->args[2])) {
                 tmp = arg_info(op->args[2])->val & 63;
-                mask = (uint64_t)arg_info(op->args[1])->mask >> tmp;
+                z_mask = (uint64_t)arg_info(op->args[1])->z_mask >> tmp;
             }
             break;
 
         case INDEX_op_extrl_i64_i32:
-            mask = (uint32_t)arg_info(op->args[1])->mask;
+            z_mask = (uint32_t)arg_info(op->args[1])->z_mask;
             break;
         case INDEX_op_extrh_i64_i32:
-            mask = (uint64_t)arg_info(op->args[1])->mask >> 32;
+            z_mask = (uint64_t)arg_info(op->args[1])->z_mask >> 32;
             break;
 
         CASE_OP_32_64(shl):
             if (arg_is_const(op->args[2])) {
                 tmp = arg_info(op->args[2])->val & (TCG_TARGET_REG_BITS - 1);
-                mask = arg_info(op->args[1])->mask << tmp;
+                z_mask = arg_info(op->args[1])->z_mask << tmp;
             }
             break;
 
         CASE_OP_32_64(neg):
             /* Set to 1 all bits to the left of the rightmost.  */
-            mask = -(arg_info(op->args[1])->mask
-                     & -arg_info(op->args[1])->mask);
+            z_mask = -(arg_info(op->args[1])->z_mask
+                       & -arg_info(op->args[1])->z_mask);
             break;
 
         CASE_OP_32_64(deposit):
-            mask = deposit64(arg_info(op->args[1])->mask,
-                             op->args[3], op->args[4],
-                             arg_info(op->args[2])->mask);
+            z_mask = deposit64(arg_info(op->args[1])->z_mask,
+                               op->args[3], op->args[4],
+                               arg_info(op->args[2])->z_mask);
             break;
 
         CASE_OP_32_64(extract):
-            mask = extract64(arg_info(op->args[1])->mask,
-                             op->args[2], op->args[3]);
+            z_mask = extract64(arg_info(op->args[1])->z_mask,
+                               op->args[2], op->args[3]);
             if (op->args[2] == 0) {
-                affected = arg_info(op->args[1])->mask & ~mask;
+                affected = arg_info(op->args[1])->z_mask & ~z_mask;
             }
             break;
         CASE_OP_32_64(sextract):
-            mask = sextract64(arg_info(op->args[1])->mask,
-                              op->args[2], op->args[3]);
-            if (op->args[2] == 0 && (tcg_target_long)mask >= 0) {
-                affected = arg_info(op->args[1])->mask & ~mask;
+            z_mask = sextract64(arg_info(op->args[1])->z_mask,
+                                op->args[2], op->args[3]);
+            if (op->args[2] == 0 && (tcg_target_long)z_mask >= 0) {
+                affected = arg_info(op->args[1])->z_mask & ~z_mask;
             }
             break;
 
         CASE_OP_32_64(or):
         CASE_OP_32_64(xor):
-            mask = arg_info(op->args[1])->mask | arg_info(op->args[2])->mask;
+            z_mask = arg_info(op->args[1])->z_mask
+                   | arg_info(op->args[2])->z_mask;
             break;
 
         case INDEX_op_clz_i32:
         case INDEX_op_ctz_i32:
-            mask = arg_info(op->args[2])->mask | 31;
+            z_mask = arg_info(op->args[2])->z_mask | 31;
             break;
 
         case INDEX_op_clz_i64:
         case INDEX_op_ctz_i64:
-            mask = arg_info(op->args[2])->mask | 63;
+            z_mask = arg_info(op->args[2])->z_mask | 63;
             break;
 
         case INDEX_op_ctpop_i32:
-            mask = 32 | 31;
+            z_mask = 32 | 31;
             break;
         case INDEX_op_ctpop_i64:
-            mask = 64 | 63;
+            z_mask = 64 | 63;
             break;
 
         CASE_OP_32_64(setcond):
         case INDEX_op_setcond2_i32:
-            mask = 1;
+            z_mask = 1;
             break;
 
         CASE_OP_32_64(movcond):
-            mask = arg_info(op->args[3])->mask | arg_info(op->args[4])->mask;
+            z_mask = arg_info(op->args[3])->z_mask
+                   | arg_info(op->args[4])->z_mask;
             break;
 
         CASE_OP_32_64(ld8u):
-            mask = 0xff;
+            z_mask = 0xff;
             break;
         CASE_OP_32_64(ld16u):
-            mask = 0xffff;
+            z_mask = 0xffff;
             break;
         case INDEX_op_ld32u_i64:
-            mask = 0xffffffffu;
+            z_mask = 0xffffffffu;
             break;
 
         CASE_OP_32_64(qemu_ld):
@@ -1026,43 +1028,43 @@ void tcg_optimize(TCGContext *s)
                 MemOpIdx oi = op->args[nb_oargs + nb_iargs];
                 MemOp mop = get_memop(oi);
                 if (!(mop & MO_SIGN)) {
-                    mask = (2ULL << ((8 << (mop & MO_SIZE)) - 1)) - 1;
+                    z_mask = (2ULL << ((8 << (mop & MO_SIZE)) - 1)) - 1;
                 }
             }
             break;
 
         CASE_OP_32_64(bswap16):
-            mask = arg_info(op->args[1])->mask;
-            if (mask <= 0xffff) {
+            z_mask = arg_info(op->args[1])->z_mask;
+            if (z_mask <= 0xffff) {
                 op->args[2] |= TCG_BSWAP_IZ;
             }
-            mask = bswap16(mask);
+            z_mask = bswap16(z_mask);
             switch (op->args[2] & (TCG_BSWAP_OZ | TCG_BSWAP_OS)) {
             case TCG_BSWAP_OZ:
                 break;
             case TCG_BSWAP_OS:
-                mask = (int16_t)mask;
+                z_mask = (int16_t)z_mask;
                 break;
             default: /* undefined high bits */
-                mask |= MAKE_64BIT_MASK(16, 48);
+                z_mask |= MAKE_64BIT_MASK(16, 48);
                 break;
             }
             break;
 
         case INDEX_op_bswap32_i64:
-            mask = arg_info(op->args[1])->mask;
-            if (mask <= 0xffffffffu) {
+            z_mask = arg_info(op->args[1])->z_mask;
+            if (z_mask <= 0xffffffffu) {
                 op->args[2] |= TCG_BSWAP_IZ;
             }
-            mask = bswap32(mask);
+            z_mask = bswap32(z_mask);
             switch (op->args[2] & (TCG_BSWAP_OZ | TCG_BSWAP_OS)) {
             case TCG_BSWAP_OZ:
                 break;
             case TCG_BSWAP_OS:
-                mask = (int32_t)mask;
+                z_mask = (int32_t)z_mask;
                 break;
             default: /* undefined high bits */
-                mask |= MAKE_64BIT_MASK(32, 32);
+                z_mask |= MAKE_64BIT_MASK(32, 32);
                 break;
             }
             break;
@@ -1074,9 +1076,9 @@ void tcg_optimize(TCGContext *s)
         /* 32-bit ops generate 32-bit results.  For the result is zero test
            below, we can ignore high bits, but for further optimizations we
            need to record that the high bits contain garbage.  */
-        partmask = mask;
+        partmask = z_mask;
         if (!(def->flags & TCG_OPF_64BIT)) {
-            mask |= ~(tcg_target_ulong)0xffffffffu;
+            z_mask |= ~(tcg_target_ulong)0xffffffffu;
             partmask &= 0xffffffffu;
             affected &= 0xffffffffu;
         }
@@ -1472,7 +1474,7 @@ void tcg_optimize(TCGContext *s)
                    vs the high word of the input.  */
             do_setcond_high:
                 reset_temp(op->args[0]);
-                arg_info(op->args[0])->mask = 1;
+                arg_info(op->args[0])->z_mask = 1;
                 op->opc = INDEX_op_setcond_i32;
                 op->args[1] = op->args[2];
                 op->args[2] = op->args[4];
@@ -1498,7 +1500,7 @@ void tcg_optimize(TCGContext *s)
                 }
             do_setcond_low:
                 reset_temp(op->args[0]);
-                arg_info(op->args[0])->mask = 1;
+                arg_info(op->args[0])->z_mask = 1;
                 op->opc = INDEX_op_setcond_i32;
                 op->args[2] = op->args[3];
                 op->args[3] = op->args[5];
@@ -1543,7 +1545,7 @@ void tcg_optimize(TCGContext *s)
             /* Default case: we know nothing about operation (or were unable
                to compute the operation result) so no propagation is done.
                We trash everything if the operation is the end of a basic
-               block, otherwise we only trash the output args.  "mask" is
+               block, otherwise we only trash the output args.  "z_mask" is
                the non-zero bits mask for the first output arg.  */
             if (def->flags & TCG_OPF_BB_END) {
                 memset(&temps_used, 0, sizeof(temps_used));
@@ -1554,7 +1556,7 @@ void tcg_optimize(TCGContext *s)
                     /* Save the corresponding known-zero bits mask for the
                        first output argument (only one supported so far). */
                     if (i == 0) {
-                        arg_info(op->args[i])->mask = mask;
+                        arg_info(op->args[i])->z_mask = z_mask;
                     }
                 }
             }
