Notice when the input is known to be zero-extended and force
the TCG_BSWAP_IZ flag on.  Honor the TCG_BSWAP_OS bit during
constant folding.  Propagate the input to the output mask.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 tcg/optimize.c | 56 +++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 51 insertions(+), 5 deletions(-)

diff --git a/tcg/optimize.c b/tcg/optimize.c
index 37c902283e..3b6983fbef 100644
--- a/tcg/optimize.c
+++ b/tcg/optimize.c
@@ -354,10 +354,12 @@ static uint64_t do_constant_folding_2(TCGOpcode op, uint64_t x, uint64_t y)
         return (uint16_t)x;
 
     CASE_OP_32_64(bswap16):
-        return bswap16(x);
+        x = bswap16(x);
+        return y & TCG_BSWAP_OS ? (int16_t)x : x;
 
     CASE_OP_32_64(bswap32):
-        return bswap32(x);
+        x = bswap32(x);
+        return y & TCG_BSWAP_OS ? (int32_t)x : x;
 
     case INDEX_op_bswap64_i64:
         return bswap64(x);
@@ -1028,6 +1030,42 @@ void tcg_optimize(TCGContext *s)
             }
             break;
 
+        CASE_OP_32_64(bswap16):
+            mask = arg_info(op->args[1])->mask;
+            if (mask <= 0xffff) {
+                op->args[2] |= TCG_BSWAP_IZ;
+            }
+            mask = bswap16(mask);
+            switch (op->args[2] & (TCG_BSWAP_OZ | TCG_BSWAP_OS)) {
+            case TCG_BSWAP_OZ:
+                break;
+            case TCG_BSWAP_OS:
+                mask = (int16_t)mask;
+                break;
+            default: /* undefined high bits */
+                mask |= MAKE_64BIT_MASK(16, 48);
+                break;
+            }
+            break;
+
+        case INDEX_op_bswap32_i64:
+            mask = arg_info(op->args[1])->mask;
+            if (mask <= 0xffffffffu) {
+                op->args[2] |= TCG_BSWAP_IZ;
+            }
+            mask = bswap32(mask);
+            switch (op->args[2] & (TCG_BSWAP_OZ | TCG_BSWAP_OS)) {
+            case TCG_BSWAP_OZ:
+                break;
+            case TCG_BSWAP_OS:
+                mask = (int32_t)mask;
+                break;
+            default: /* undefined high bits */
+                mask |= MAKE_64BIT_MASK(32, 32);
+                break;
+            }
+            break;
+
         default:
             break;
         }
@@ -1134,9 +1172,6 @@ void tcg_optimize(TCGContext *s)
         CASE_OP_32_64(ext16s):
         CASE_OP_32_64(ext16u):
         CASE_OP_32_64(ctpop):
-        CASE_OP_32_64(bswap16):
-        CASE_OP_32_64(bswap32):
-        case INDEX_op_bswap64_i64:
         case INDEX_op_ext32s_i64:
         case INDEX_op_ext32u_i64:
         case INDEX_op_ext_i32_i64:
@@ -1150,6 +1185,17 @@ void tcg_optimize(TCGContext *s)
             }
             goto do_default;
 
+        CASE_OP_32_64(bswap16):
+        CASE_OP_32_64(bswap32):
+        case INDEX_op_bswap64_i64:
+            if (arg_is_const(op->args[1])) {
+                tmp = do_constant_folding(opc, arg_info(op->args[1])->val,
+                                          op->args[2]);
+                tcg_opt_gen_movi(s, &temps_used, op, op->args[0], tmp);
+                break;
+            }
+            goto do_default;
+
         CASE_OP_32_64(add):
         CASE_OP_32_64(sub):
         CASE_OP_32_64(mul):
-- 
2.25.1

On Mon, 14 Jun 2021 at 09:45, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Notice when the input is known to be zero-extended and force
> the TCG_BSWAP_IZ flag on.  Honor the TCG_BSWAP_OS bit during
> constant folding.  Propagate the input to the output mask.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  tcg/optimize.c | 56 +++++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 51 insertions(+), 5 deletions(-)

Not really familiar with the TCG optimizer internals, so review
from somebody who is would be useful, but this looks plausible:

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM