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Re: [tree-ssa] Fix cgraph related PR opt/13729
> On Sun, 18 Jan 2004, Jan Hubicka wrote:
> > I also included patch to remove releavant changes in fold-const so the
> > combining does not happen early.
> > I am not quite sure what approach is better, both has it's advantages and
> > disadvantages. I will run SPECs on combination of these patches on x86-64
> > and alpha and send results.
> > Sat Jun 1 20:10:19 CEST 2002 Jan Hubicka <email@example.com>
> > * fold-const.c (RANGE_TEST_NON_SHORT_CIRCUIT): Kill.
> > (fold_range_test): Kill branch combining.
> > (fold_truthop): Kill branch combining.
> Hi Jan,
> Rather than simply delete these optimizations, have you considered
> simply changing their conditions such that they only trigger for
> "BRANCH_COST >= 3" or "BRANCH_COST >= 4"? You've only recently
> increased the default BRANCH_COST for x86 to two, so this could
> simply be an issue with parameter fine tuning.
> I'd much rather that we are more selective about whether an
> optimization fires or not, rather than simply remove it completely
> from the source code [unless of course, its clearly a looser].
> There may be non IA-32 platforms that still benefit from these
> transformations! And we still don't have the benchmark results
> for IA-32 yet.
The idea has been that the ifcvt patch will take care of these
transfomration later when it has more information about their
profitability. Doing the transformation early confuse some other
optimizations such as jump threading, constant propagation and such,
becuase originally parseable conditionals were replaced.
The tree-SSA for instance has one or two testcases on CCP that are fixed
by removing these transformations.