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[Bug tree-optimization/50557] [4.7 Regression] Register pressure increase after reassociation (x86, 32 bits)
- From: "wschmidt at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Mon, 10 Oct 2011 12:40:01 +0000
- Subject: [Bug tree-optimization/50557] [4.7 Regression] Register pressure increase after reassociation (x86, 32 bits)
- Auto-submitted: auto-generated
- References: <bug-50557-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50557
--- Comment #7 from William J. Schmidt <wschmidt at gcc dot gnu.org> 2011-10-10 12:40:01 UTC ---
I don't have anything too helpful to add. This code as it stands is balanced
on a knife's edge for register usage for the particular target, so it's always
going to be sensitive to compiler changes (not just this one).
One thing I notice is that the loop is hand-unrolled four times. Why not let
the compiler intelligently choose the unroll factor? I don't know what the
result would be, but presumably the unroller has some heuristics to take target
characteristics into account. Seems to me the factor of 4 is a bit aggressive
for this target.