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tcg/optimize: optimize "op r, a, a => movi r, 0"

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Now that it's possible to detect copies, we can optimize the case
the "op r, a, a => movi r, 0". This helps in the computation of
overflow flags when one of the two args is 0.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
This commit is contained in:
Aurelien Jarno 2012-09-18 19:12:36 +02:00
parent 0aba1c7376
commit 3c94193e0b
1 changed files with 16 additions and 0 deletions
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16
tcg/optimize.c
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@ -540,6 +540,22 @@ static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
break; break;
} }
/* Simplify expression for "op r, a, a => movi r, 0" cases */
switch (op) {
CASE_OP_32_64(sub):
CASE_OP_32_64(xor):
if (temps_are_copies(args[1], args[2])) {
gen_opc_buf[op_index] = op_to_movi(op);
tcg_opt_gen_movi(gen_args, args[0], 0);
gen_args += 2;
args += 3;
continue;
}
break;
default:
break;
}
/* Propagate constants through copy operations and do constant /* Propagate constants through copy operations and do constant
folding. Constants will be substituted to arguments by register folding. Constants will be substituted to arguments by register
allocator where needed and possible. Also detect copies. */ allocator where needed and possible. Also detect copies. */