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simplify-rtx: Simplify sign_extend of lshiftrt to zero_extend (PR68330) 

Since r230164, in PR68330 combine ends up with a sign_extend of an
lshiftrt by some constant, and it does not know to morph that into a
zero_extract (the extend will always extend with zeroes).  I think
it is best to let simplify-rtx always replace such a sign_extend by
a zero_extend, after which everything works as expected.


2015-11-15  Segher Boessenkool  <segher@kernel.crashing.org>

	PR rtl-optimization/68330
	* simplify-rtx.c (simplify_unary_operation_1): Simplify SIGN_EXTEND
	of LSHIFTRT by a non-zero constant integer.

From-SVN: r230429
This commit is contained in:
Segher Boessenkool 2015-11-16 16:51:33 +01:00 committed by Segher Boessenkool
parent 513ecaea6f
commit 7d006b0d34
2 changed files with 13 additions and 0 deletions
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gcc/ChangeLog
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@ -1,3 +1,9 @@
2015-11-16 Segher Boessenkool <segher@kernel.crashing.org>
PR rtl-optimization/68330
* simplify-rtx.c (simplify_unary_operation_1): Simplify SIGN_EXTEND
of LSHIFTRT by a non-zero constant integer.
2015-11-16 Richard Biener <rguenther@suse.de>
PR tree-optimization/68306

7
gcc/simplify-rtx.c
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@ -1462,6 +1462,13 @@ simplify_unary_operation_1 (enum rtx_code code, machine_mode mode, rtx op)
}
}
/* (sign_extend:M (lshiftrt:N <X> (const_int I))) is better as
(zero_extend:M (lshiftrt:N <X> (const_int I))) if I is not 0. */
if (GET_CODE (op) == LSHIFTRT
&& CONST_INT_P (XEXP (op, 1))
&& XEXP (op, 1) != const0_rtx)
return simplify_gen_unary (ZERO_EXTEND, mode, op, GET_MODE (op));
#if defined(POINTERS_EXTEND_UNSIGNED)
/* As we do not know which address space the pointer is referring to,
we can do this only if the target does not support different pointer