[llvm-bugs] [Bug 47221] New: Miscompile with collapse(4) on a triangular loop nest

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=47221

            Bug ID: 47221
           Summary: Miscompile with collapse(4) on a triangular loop nest
           Product: OpenMP
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Clang Compiler Support
          Assignee: unassignedclangbugs at nondot.org
          Reporter: huberjn at ornl.gov
                CC: llvm-bugs at lists.llvm.org

Created attachment 23859
  --> https://bugs.llvm.org/attachment.cgi?id=23859&action=edit
Makefile and test code used on x86-64 Linux with clang trunk to produce the
error.

The following triangular loop nest miscompiles on trunk when attempting to
collapse the whole loop nest. Device code is not generated causing `undefined
reference to` errors in the device linker.

https://godbolt.org/z/1xv6Eo

Using collapse(3) on the outer loop, the program compiles without errors but
miscompiles and returns incorrect values. Collapsing with < 3 works as expected
as does collapsing on the second loop instead.

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