[llvm-bugs] [Bug 43414] New: DAGCombiner never finishes

via llvm-bugs llvm-bugs at lists.llvm.org
Mon Sep 23 10:51:37 PDT 2019


            Bug ID: 43414
           Summary: DAGCombiner never finishes
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: trass3r at gmail.com
                CC: llvm-bugs at lists.llvm.org, neeilans at live.com,
                    richard-llvm at metafoo.co.uk

Created attachment 22549
  --> https://bugs.llvm.org/attachment.cgi?id=22549&action=edit
test files

$ clang++ -O2 -fno-exceptions -fno-rtti -c test.cpp -ftime-trace
seems to be stuck in DAGCombiner, even after 20 minutes.

test.smaller.cpp finishes after 2 minutes and spends its time in InstCombine
mainly. The generated code is really bad, tens of thousands of mov dword ptr
[rsp + i], x
It's possible to force it to do the right thing with an explicit constexpr but
that shouldn't be necessary.

$ clang++ -v
clang version 10.0.0 (https://github.com/llvm/llvm-project.git
Target: x86_64-pc-windows-msvc

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