Re: [Qemu-devel] [PATCH] Fix extlh instruction on Alpha

[Vince Weaver <vince@csl.cornell.edu>]

On Wed, 16 Sep 2009, Aurelien Jarno wrote:

> In case tmp1 = 0, it becomes 64, and then 0 again after the and, so
> rc=ra<<0.

Ah, I see.  I completely missed that optimization.

How does this updated patch look?  I removed one of the TCGv variables 
too.  Does that help performance?  What would be nice is a tcg 
subtract-from instruction, which I know some architectures have.  Maybe 
tcg does have it and I should look harder.



diff --git a/target-alpha/translate.c b/target-alpha/translate.c
index 9d2bc45..af2a43c 100644
--- a/target-alpha/translate.c
+++ b/target-alpha/translate.c
@@ -524,14 +524,16 @@ static inline void gen_ext_h(void(*tcg_gen_ext_i64)(TCGv t0, TCGv t1),
             else
                 tcg_gen_mov_i64(cpu_ir[rc], cpu_ir[ra]);
         } else {
-            TCGv tmp1, tmp2;
+            TCGv tmp1;
             tmp1 = tcg_temp_new();
+
             tcg_gen_andi_i64(tmp1, cpu_ir[rb], 7);
             tcg_gen_shli_i64(tmp1, tmp1, 3);
-            tmp2 = tcg_const_i64(64);
-            tcg_gen_sub_i64(tmp1, tmp2, tmp1);
-            tcg_temp_free(tmp2);
+            tcg_gen_andi_i64(tmp1, tmp1, 0x3f);
+            tcg_gen_neg_i64(tmp1, tmp1);
+            tcg_gen_addi_i64(tmp1, tmp1, 64);
             tcg_gen_shl_i64(cpu_ir[rc], cpu_ir[ra], tmp1);
+
             tcg_temp_free(tmp1);
         }
         if (tcg_gen_ext_i64)
@@ -1316,7 +1318,7 @@ static inline int translate_one(DisasContext *ctx, uint32_t insn)
             break;
         case 0x6A:
             /* EXTLH */
-            gen_ext_h(&tcg_gen_ext16u_i64, ra, rb, rc, islit, lit);
+            gen_ext_h(&tcg_gen_ext32u_i64, ra, rb, rc, islit, lit);
             break;
         case 0x72:
             /* MSKQH */