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simplify-rtx: Simplify trunc of and of shiftrt 

If we have

	(truncate:M1 (and:M2 (lshiftrt:M2 (x:M2) C) C2))

we can write it instead as

	(and:M1 (lshiftrt:M1 (truncate:M1 (x:M2)) C) C2)

(if that is valid, of course), which has smaller modes for the
binary ops, and the truncate can often simplify further (if "x"
is a register, for example).


	* gcc/simplify-rtx.c (simplify_truncation): Simplify TRUNCATE
	of AND of [LA]SHIFTRT.

From-SVN: r230164
This commit is contained in:
Segher Boessenkool 2015-11-11 15:09:30 +01:00 committed by Segher Boessenkool
parent 7ad291c0e8
commit 3b1da8bb77
2 changed files with 33 additions and 0 deletions
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
2015-11-11 Segher Boessenkool <segher@kernel.crashing.org>
* gcc/simplify-rtx.c (simplify_truncation): Simplify TRUNCATE
of AND of [LA]SHIFTRT.
2015-11-11 Martin Liska <mliska@suse.cz>
Richard Biener <rguenther@suse.de>

28
gcc/simplify-rtx.c
View File

@ -714,6 +714,34 @@ simplify_truncation (machine_mode mode, rtx op,
return simplify_gen_binary (ASHIFT, mode,
XEXP (XEXP (op, 0), 0), XEXP (op, 1));
/* Likewise (truncate:QI (and:SI (lshiftrt:SI (x:SI) C) C2)) into
(and:QI (lshiftrt:QI (truncate:QI (x:SI)) C) C2) for suitable C
and C2. */
if (GET_CODE (op) == AND
&& (GET_CODE (XEXP (op, 0)) == LSHIFTRT
|| GET_CODE (XEXP (op, 0)) == ASHIFTRT)
&& CONST_INT_P (XEXP (XEXP (op, 0), 1))
&& CONST_INT_P (XEXP (op, 1)))
{
rtx op0 = (XEXP (XEXP (op, 0), 0));
rtx shift_op = XEXP (XEXP (op, 0), 1);
rtx mask_op = XEXP (op, 1);
unsigned HOST_WIDE_INT shift = UINTVAL (shift_op);
unsigned HOST_WIDE_INT mask = UINTVAL (mask_op);
if (shift < precision
/* If doing this transform works for an X with all bits set,
it works for any X. */
&& ((GET_MODE_MASK (mode) >> shift) & mask)
== ((GET_MODE_MASK (op_mode) >> shift) & mask)
&& (op0 = simplify_gen_unary (TRUNCATE, mode, op0, op_mode))
&& (op0 = simplify_gen_binary (LSHIFTRT, mode, op0, shift_op)))
{
mask_op = GEN_INT (trunc_int_for_mode (mask, mode));
return simplify_gen_binary (AND, mode, op0, mask_op);
}
}
/* Recognize a word extraction from a multi-word subreg. */
if ((GET_CODE (op) == LSHIFTRT
|| GET_CODE (op) == ASHIFTRT)