The existing interpreter zero-extends, ignoring high bits.
Simply add a separate sign-extension opcode if required.
Ensure that the interpreter supports ext16s when bswap16 is enabled.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 tcg/tci.c                |  3 ++-
 tcg/tci/tcg-target.c.inc | 23 ++++++++++++++++++++---
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/tcg/tci.c b/tcg/tci.c
index d68c5a4e55..109522a865 100644
--- a/tcg/tci.c
+++ b/tcg/tci.c
@@ -733,7 +733,8 @@ uintptr_t QEMU_DISABLE_CFI tcg_qemu_tb_exec(CPUArchState *env,
             regs[r0] = (int8_t)regs[r1];
             break;
 #endif
-#if TCG_TARGET_HAS_ext16s_i32 || TCG_TARGET_HAS_ext16s_i64
+#if TCG_TARGET_HAS_ext16s_i32 || TCG_TARGET_HAS_ext16s_i64 || \
+    TCG_TARGET_HAS_bswap16_i32 || TCG_TARGET_HAS_bswap16_i64
         CASE_32_64(ext16s)
             tci_args_rr(&tb_ptr, &r0, &r1);
             regs[r0] = (int16_t)regs[r1];
diff --git a/tcg/tci/tcg-target.c.inc b/tcg/tci/tcg-target.c.inc
index 823ecd5d35..1e92688dca 100644
--- a/tcg/tci/tcg-target.c.inc
+++ b/tcg/tci/tcg-target.c.inc
@@ -617,6 +617,8 @@ static void tcg_out_op(TCGContext *s, TCGOpcode opc,
                        const TCGArg args[TCG_MAX_OP_ARGS],
                        const int const_args[TCG_MAX_OP_ARGS])
 {
+    TCGOpcode exts;
+
     switch (opc) {
     case INDEX_op_exit_tb:
         tcg_out_op_p(s, opc, (void *)args[0]);
@@ -710,12 +712,27 @@ static void tcg_out_op(TCGContext *s, TCGOpcode opc,
     CASE_64(ext32u)      /* Optional (TCG_TARGET_HAS_ext32u_i64). */
     CASE_64(ext_i32)
     CASE_64(extu_i32)
-    CASE_32_64(bswap16)  /* Optional (TCG_TARGET_HAS_bswap16_*). */
-    CASE_32_64(bswap32)  /* Optional (TCG_TARGET_HAS_bswap32_*). */
-    CASE_64(bswap64)     /* Optional (TCG_TARGET_HAS_bswap64_i64). */
+    case INDEX_op_bswap32_i32: /* Optional (TCG_TARGET_HAS_bswap32_i32). */
+    case INDEX_op_bswap64_i64: /* Optional (TCG_TARGET_HAS_bswap64_i64). */
         tcg_out_op_rr(s, opc, args[0], args[1]);
         break;
 
+    case INDEX_op_bswap16_i32: /* Optional (TCG_TARGET_HAS_bswap16_i32). */
+        exts = INDEX_op_ext16s_i32;
+        goto do_bswap;
+    case INDEX_op_bswap16_i64: /* Optional (TCG_TARGET_HAS_bswap16_i64). */
+        exts = INDEX_op_ext16s_i64;
+        goto do_bswap;
+    case INDEX_op_bswap32_i64: /* Optional (TCG_TARGET_HAS_bswap32_i64). */
+        exts = INDEX_op_ext32s_i64;
+    do_bswap:
+        /* The base tci bswaps zero-extend, and ignore high bits. */
+        tcg_out_op_rr(s, opc, args[0], args[1]);
+        if (args[2] & TCG_BSWAP_OS) {
+            tcg_out_op_rr(s, exts, args[0], args[0]);
+        }
+        break;
+
 #if TCG_TARGET_REG_BITS == 32
     case INDEX_op_add2_i32:
     case INDEX_op_sub2_i32:
-- 
2.25.1

On 6/14/21 10:37 AM, Richard Henderson wrote:
> The existing interpreter zero-extends, ignoring high bits.
> Simply add a separate sign-extension opcode if required.
> Ensure that the interpreter supports ext16s when bswap16 is enabled.
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  tcg/tci.c                |  3 ++-
>  tcg/tci/tcg-target.c.inc | 23 ++++++++++++++++++++---
>  2 files changed, 22 insertions(+), 4 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>