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From: "wilson at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/94092] Code size and performance degradations
 after -ftree-loop-distribute-patterns was enabled at -O[2s]+
Date: Tue, 23 Feb 2021 23:57:36 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94092

--- Comment #6 from Jim Wilson <wilson at gcc dot gnu.org> ---
Trying Alex's patch, it doesn't work on this testcase.

One problem is that the loop bound is unknown, so the memset size is estima=
ted
as max 0x1fffffffc bytes.  The code calls
default_use_by_pieces_infrastructure_p which wants the total number of
instructions to be less than SET_RATIO which is 16.  The total number of
instructions is computed as 0x1fffffffc.  So the attempt fails.

There is a contributing problem here that the alignment of the dest was
computed as 8-bits, even though we have a pointer to int which has 32-bit
alignment on a strict alignment system.  That problem happens in
expand_builtin_memset_args which calls get_pointer_alignment on dest.  DEST=
 is
a SSN_NAME, and the SSA_NAME pointer info says align is 0, so it defaults to
8-bit byte alignment.  I haven't tried to figure out where that went wrong.

The patch does work as advertised on libgcc soft-float code.  For an rv32i
build I see the memset calls in libgcc.a reduced from 31 to 10.=