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From: "ustcw0ng at mail dot ustc.edu.cn" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/99823] New: -funroll-all-loops bugs when using contexpr
 variable
Date: Tue, 30 Mar 2021 04:42:34 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99823

            Bug ID: 99823
           Summary: -funroll-all-loops bugs when using contexpr variable
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ustcw0ng at mail dot ustc.edu.cn
  Target Milestone: ---

Created attachment 50483
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D50483&action=3Dedit
constexpr.cpp && unroll.cpp

-funroll-all-loops indicates "Unroll all loops, even if their number of
iterations is uncertain when the loop is entered. This usually makes progra=
ms
run more slowly.". But in the following example constexpr.cpp can never tur=
n to
unroll.cpp, even if number of iterations is certain due to constexpr.

compiler flag: -O3 -std=3Dc++2a -DNDEBUG -funroll-all-loops=