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Re: [Qemu-devel] [PATCH RFC v1 1/3] target/ppc: Emulate LL/SC using cmpx

From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH RFC v1 1/3] target/ppc: Emulate LL/SC using cmpxchg helpers
Date: Thu, 6 Apr 2017 08:51:52 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

On 04/06/2017 03:22 AM, Nikunj A Dadhania wrote:
+    TCGv_i32 tmp = tcg_temp_local_new_i32();
+    TCGv t0;

+    tcg_gen_movi_i32(tmp, 0);
     tcg_gen_trunc_tl_i32(cpu_crf[0], cpu_so);
     l1 = gen_new_label();
     tcg_gen_brcond_tl(TCG_COND_NE, EA, cpu_reserve, l1);
-    tcg_gen_ori_i32(cpu_crf[0], cpu_crf[0], CRF_EQ);
-    tcg_gen_qemu_st_tl(cpu_gpr[reg], EA, ctx->mem_idx, memop);
+    t0 = tcg_temp_new();
+    tcg_gen_atomic_cmpxchg_tl(t0, EA, cpu_reserve_val, cpu_gpr[reg],
+                              ctx->mem_idx, DEF_MEMOP(memop));
+    tcg_gen_setcond_tl(TCG_COND_EQ, t0, t0, cpu_reserve_val);
+    tcg_gen_trunc_tl_i32(tmp, t0);
+    tcg_gen_shli_i32(tmp, tmp, CRF_EQ_BIT);
+    tcg_gen_or_i32(cpu_crf[0], cpu_crf[0], tmp);

I encourage you to move these two lines up beside the setcond.
That way you don't need to use a local tmp, which implies a
spill/restore from the stack.


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