[llvm-bugs] [Bug 39836] New: Significant build time regression since SVN r347776, "[LICM] Reapply r347190 "Make LICM able to hoist phis" with fix"

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=39836

            Bug ID: 39836
           Summary: Significant build time regression since SVN r347776,
                    "[LICM] Reapply r347190 "Make LICM able to hoist phis"
                    with fix"
           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: john.brawn at arm.com, llvm-bugs at lists.llvm.org,
                    max.kazantsev at azul.com

Created attachment 21177
  --> https://bugs.llvm.org/attachment.cgi?id=21177&action=edit
Compressed reproduction sample

Since "[LICM] Reapply r347190 "Make LICM able to hoist phis" with fix", the
build time of one source file has regressed significantly.

With the attached sample file, before SVN r347776, compiling this source file
took ~45 seconds:

$ time clang -target i686-w64-mingw32 -O2 -c glew-preproc.c

real    0m46.052s
user    0m45.676s
sys     0m0.368s

After this change, building now takes over 140 seconds:

$ time clang -target i686-w64-mingw32 -O2 -c glew-preproc.c

real    2m22.770s
user    2m22.224s
sys     0m0.492s

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