On Thu, Aug 20, 2015 at 10:22 AM, Bin.Cheng <amker.ch...@gmail.com> wrote: > On Fri, Aug 14, 2015 at 4:28 PM, Richard Biener > <richard.guent...@gmail.com> wrote: >> 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. > Yes, this is corner case targeting induction variables of small signed > types, just like added test cases. We need to convert it to unsigned, > do the stepping, and convert back. I collected statistics for gcc > bootstrap and spec2k6. The function is called about 400-500 times in > both case. About 45% of calls succeeded in bootstrap, while only ~3% > succeeded in spec2k6. > > I will prepare a new version patch if you think it's worthwhile in > terms of compilation cost and benefit.
Yes. Richard. > Thanks, > bin >> >> + || !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.