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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/55894] No constant propagation in Intel intrinsics
Date: Mon, 07 Jan 2013 14:26:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55894

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-01-07 14:25:33 UTC ---
The reason why it doesn't happen during combine is that the insns don't allow
constants, they require loads from memory, so while the compiler is aware
of the folded constant, e.g. in the g function:
(insn 12 7 15 2 (set (reg/i:V2DF 21 xmm0)
        (subreg:V2DF (reg:V2DI 65 [ D.4526 ]) 0)) pr55894.c:16 1157
{*movv2df_internal}
     (expr_list:REG_DEAD (reg:V2DI 65 [ D.4526 ])
        (expr_list:REG_EQUAL (const_vector:V2DF [
                    (const_double:DF +QNaN [+QNaN])
                    (const_double:DF +QNaN [+QNaN])
                ])
            (nil))))
it fails to match and thus isn't actually used in the code.  A pass that would
see you load a constant from memory, do some transformations on it which are
all foldable by the compiler and transforming that into just load of a
different constant could handle this (or do it in combine?), but the problem
with that is that it could in theory increase the constant pool too much.