Hi Andrew, Thanks for your detailed comment. There are two problem I wanted to discuss with you about:
a) The optimization I have sent patch, does optimize variable length "<<" too(for example B0 << x, where x is variable). This [1] link shows the actual optimization and a link for the proof is included in the editor. b) I am unable to prove the optimization you are describing for non-constant length shift. You can take a look at the code example [2] and proof [3]. I am getting "Transformation doesn't verify!" when I do implement the optimization you mentioned for non-constant shift. The optimization you are describing only works for "(take: (t << 1) != 0) -> ((t & 0x7fffffff) != 0)" which only is provable and works for INTEGER_CST. My understanding might be incorrect here, please don't hesitate to correct me. 1) https://compiler-explorer.com/z/r46znh4Tj 2) https://compiler-explorer.com/z/K1so39dbK 3) https://alive2.llvm.org/ce/z/-54zZv Best wishes, Navid. ________________________________________ From: Andrew Pinski <pins...@gmail.com> Sent: Tuesday, November 30, 2021 14:03 To: Navid Rahimi Cc: Navid Rahimi via Gcc-patches Subject: [EXTERNAL] Re: [PATCH] tree-optimization/98956 Optimizing out boolean left shift On Tue, Nov 30, 2021 at 8:35 AM Navid Rahimi via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > > Hi GCC community, > > This patch will add the missed pattern described in bug 98956 [1] to the > match.pd. The codegen and correctness proof for this pattern is here [2,3] in > case anyone is curious. Tested on x86_64 Linux. > A better way to optimize this is the following (which I describe in PR 64992): take: (t << 1) != 0; This should be transformed into: (t & 0x7fffffff) != 0 The rest will just fall out really. That is there is no reason to special case bool here. I have most of the patch except for creating the mask part which should be simple, I just did not want to look up the wi:: functions at the time I was writing it into the bug report. Thanks, Andrew Pinski > Tree-optimization/98956: > > Adding new optimization to match.pd: > * match.pd ((B0 << x) cmp 0) -> B0 cmp 0 : New optimization. > * gcc.dg/tree-ssa/pr98956.c: testcase for this optimization. > * gcc.dg/tree-ssa/pr98956-2.c: testcase for node with > side-effect. > > 1) > https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgcc.gnu.org%2Fbugzilla%2Fshow_bug.cgi%3Fid%3D98956&data=04%7C01%7Cnavidrahimi%40microsoft.com%7Cd83f36080fd94b563ab608d9b44d4d1f%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637739066369079450%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=EO7zAIa9sux4JklTDeALImoX3Kcjqeug%2BssU0E%2Fp6mY%3D&reserved=0 > 2) > https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcompiler-explorer.com%2Fz%2Fnj4PTrecW&data=04%7C01%7Cnavidrahimi%40microsoft.com%7Cd83f36080fd94b563ab608d9b44d4d1f%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637739066369079450%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=GyivNuda31%2FPXJQQ4Z9tK2cFtj3N9YcvRdtM7rVkhHg%3D&reserved=0 > 3) > https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Falive2.llvm.org%2Fce%2Fz%2FjyJAoS&data=04%7C01%7Cnavidrahimi%40microsoft.com%7Cd83f36080fd94b563ab608d9b44d4d1f%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637739066369079450%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=esqOKjKS5JZDbNBmAi0Bwwk0JTTHzInQ2Lgeq%2BPHJ9w%3D&reserved=0 > > Best wishes, > Navid.
