On Tue, Jul 28, 2015 at 11:38 AM, Bin Cheng <bin.ch...@arm.com> wrote: > Hi, > For now, SCEV may compute iv base in the form of "(signed T)((unsigned > T)base + step))". This complicates other optimizations/analysis depending > on SCEV because it's hard to dive into type conversions. For many cases, > such type conversions can be simplified with additional range information > implied by loop initial conditions. This patch does such simplification. > With simplified iv base, loop niter analysis can compute more accurate bound > information since sensible value range can be derived for "base+step". For > example, accurate loop bound&may_be_zero information is computed for cases > added by this patch. > The code is actually borrowed from loop_exits_before_overflow. Moreover, > with simplified iv base, the second case handled in that function now > becomes the first case. I didn't remove that part of code because it may(?) > still be visited in scev analysis itself and simple_iv isn't an interface > for that. > > Is it OK?
It looks quite special given it only handles a very specific pattern. Did you do any larger collecting of statistics on how many times this triggers, esp. how many times simplify_using_initial_conditions succeeds and how many times not? This function is somewhat expensive. + || !operand_equal_p (iv->step, + fold_convert (type, + TREE_OPERAND (e, 1)), 0)) operand_equal_p can handle sign-differences in integer constants, no need to fold_convert here. Also if you know that you are comparing integer constants please use tree_int_cst_equal_p. + extreme = lower_bound_in_type (type, type); that's a strange function to call here (with two same types). Looks like just wide_int_to_tree (type, wi::max/min_value (type)). + extreme = fold_build2 (MINUS_EXPR, type, extreme, iv->step); so as iv->step is an INTEGER_CST please do this whole thing using wide_ints and only build trees here: + e = fold_build2 (code, boolean_type_node, base, extreme); Thanks, Richard. > Thanks, > bin > > 2015-07-28 Bin Cheng <bin.ch...@arm.com> > > * tree-ssa-loop-niter.c (tree_simplify_using_condition): Export > the interface. > * tree-ssa-loop-niter.h (tree_simplify_using_condition): Declare. > * tree-scalar-evolution.c (simple_iv): Simplify type conversions > in iv base using loop initial conditions. > > gcc/testsuite/ChangeLog > 2015-07-28 Bin Cheng <bin.ch...@arm.com> > > * gcc.dg/tree-ssa/loop-bound-2.c: New test. > * gcc.dg/tree-ssa/loop-bound-4.c: New test. > * gcc.dg/tree-ssa/loop-bound-6.c: New test.
