On Mon, Aug 8, 2022 at 11:06 AM Roger Sayle <ro...@nextmovesoftware.com> wrote: > > > This patch resolves both PR tree-optimization/64992 and PR > tree-optimization/98956 which are missed optimization enhancement > request, for which Andrew Pinski already has a proposed solution > (related to a fix for PR tree-optimization/98954). Yesterday, > I proposed an alternate improved patch for PR98954, which although > superior in most respects, alas didn't address this case [which > doesn't include a BIT_AND_EXPR], hence this follow-up fix. > > For many functions, F(B), of a (zero-one) Boolean value B, the > expression F(B) != 0 can often be simplified to just B. Hence > "(B * 5) != 0" is B, "-B != 0" is B, "bswap(B) != 0" is B, > "(B >>r 3) != 0" is B. These are all currently optimized by GCC, > with the strange exception of left shifts by a constant (possibly > due to the undefined/implementation defined behaviour when the > shift constant is larger than the first operand's precision). > This patch adds support for this particular case, when the shift > constant is valid. > > This patch has been tested on x86_64-pc-linux-gnu with make bootstrap > and make -k check, both with and without --target_board=unix{-m32}, > with no new failures. Ok for mainline?
+/* (X << C) != 0 can be simplified to X, when X is zero_one_valued_p. */ +(simplify + (ne (lshift zero_one_valued_p@0 INTEGER_CST@1) integer_zerop@2) + (if (tree_fits_shwi_p (@1) + && tree_to_shwi (@1) > 0 + && tree_to_shwi (@1) < TYPE_PRECISION (TREE_TYPE (@0))) + (convert @0))) while we deliberately do not fold int << 34 since the result is undefined there is IMHO no reason to not fold the above for any (even non-constant) shift value. We have guards with TYPE_OVERFLOW_SANITIZED in some cases but I think that's not appropriate here, there's one flag_sanitize check, maybe there's a special bit for SHIFT overflow we can use. Why is (X << 0) != 0 excempt in the condition? > > 2022-08-08 Roger Sayle <ro...@nextmovesoftware.com> > > gcc/ChangeLog > PR tree-optimization/64992 > PR tree-optimization/98956 > * match.pd (ne (lshift @0 @1) 0): Simplify (X << C) != 0 to X > when X is zero_one_valued_p and the shift constant C is valid. > (eq (lshift @0 @1) 0): Likewise, simplify (X << C) == 0 to !X > when X is zero_one_valued_p and the shift constant C is valid. > > gcc/testsuite/ChangeLog > PR tree-optimization/64992 > * gcc.dg/pr64992.c: New test case. > > > Thanks in advance, > Roger > -- >