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From: "pskocik at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c/98418] New: Valid integer constant expressions based on
 expressions that trigger -Wshift-overflow are treated as non-constants
Date: Tue, 22 Dec 2020 10:47:14 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98418

            Bug ID: 98418
           Summary: Valid integer constant expressions based on
                    expressions that trigger -Wshift-overflow are treated
                    as non-constants
           Product: gcc
           Version: 6.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pskocik at gmail dot com
  Target Milestone: ---

This causes things like:

struct foo { unsigned bit: (0xffffffffll<<40)!=3D0; };

to elicit a -pedantic warning about the bitfield width not being a proper
integer constant expression, even though it is.

In other contexts, a complete compilation error might ensue:

extern int bar[ (0xffffffffll<<40)!=3D0 ]; //seen as an invalid VLA


https://gcc.godbolt.org/z/7zfz96

Neither clang nor gcc <=3D 5 appear to have this bug.

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D93241 seems related.=