[llvm-bugs] [Bug 43028] New: Regression in SVN r368898, "[RLEV] Rewrite loop exit values for multiple exit loops w/o overall loop exit count"

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https://bugs.llvm.org/show_bug.cgi?id=43028

            Bug ID: 43028
           Summary: Regression in SVN r368898, "[RLEV] Rewrite loop exit
                    values for multiple exit loops w/o overall loop exit
                    count"
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: martin at martin.st
                CC: listmail at philipreames.com, llvm-bugs at lists.llvm.org,
                    nikita.ppv at gmail.com

Created attachment 22385
  --> https://bugs.llvm.org/attachment.cgi?id=22385&action=edit
Reproduction C code

Since SVN r368898, "[RLEV] Rewrite loop exit values for multiple exit loops w/o
overall loop exit count", compilation of GLEW for x86_64 has regressed further.

Prior to this commit, compilation of the attached sample file ("clang -target
x86_64-w64-mingw32 -w -c -O3 glew-preproc-x86_64-edited.c") took 2 minutes, now
it takes close to 6 minutes.

Prior to SVN r363883, compiling this file used to take only one minute (this
previous regression is tracked in PR42357, and a potential workaround was
posted in https://reviews.llvm.org/D64533), and GCC compiles it in 5 seconds.

Whether it affects runtime is unknown, but originally (prior to r363883), the
output object file size was 650K, after that it was 1.2M, and now it's 1.5M.

The previous regression manifested itself for both 32 and 64 bit x86, but this
change only (notably) affected x86_64.

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