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Re: [Qemu-devel] [PATCH] tcg: fix dead computation for repeated input ar
From: |
Richard Henderson |
Subject: |
Re: [Qemu-devel] [PATCH] tcg: fix dead computation for repeated input arguments |
Date: |
Tue, 19 May 2015 07:46:04 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 |
On 05/19/2015 03:26 AM, Aurelien Jarno wrote:
> @@ -1522,6 +1522,9 @@ static void tcg_liveness_analysis(TCGContext *s)
> if (dead_temps[arg]) {
> dead_args |= (1 << i);
> }
> + }
> + for (i = nb_oargs; i < nb_oargs + nb_iargs; i++) {
> + arg = args[i];
> dead_temps[arg] = 0;
> }
> s->op_dead_args[oi] = dead_args;
How about another line of commentary for each loop?
Something like
/* Record arguments that die in this opcode. */
for the first and
/* Input arguments are live for preceeding opcodes. */
for the second.
As for the same loop for calls, you're right that it may well cause us to do a
tiny bit of redundant work, but nothing else bad will happen. We'll enter
temp_dead more times than necessary. I'm always skeptical about knowingly
giving a compiler bad information though. You tend to not know how data is
going to be used in future, and *then* get bad results.
r~