tcg/mips: Conditionalize tcg_out_exts_i32_i64

Since TCG_TYPE_I32 values are kept sign-extended in registers, we need not
extend if the register matches.  This is already relied upon by comparisons.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tcg/mips/tcg-target.c.inc

@@ -582,7 +582,9 @@ static void tcg_out_ext32s(TCGContext *s, TCGReg rd, TCGReg rs)
 
 static void tcg_out_exts_i32_i64(TCGContext *s, TCGReg rd, TCGReg rs)
 {
-    tcg_out_ext32s(s, rd, rs);
+    if (rd != rs) {
+        tcg_out_ext32s(s, rd, rs);
+    }
 }
 
 static void tcg_out_extu_i32_i64(TCGContext *s, TCGReg rd, TCGReg rs)