[llvm-bugs] [Bug 35774] New: "Simplify the CFG" pass moves musttail call from tail position

via llvm-bugs llvm-bugs at lists.llvm.org
Fri Dec 29 16:45:58 PST 2017


            Bug ID: 35774
           Summary: "Simplify the CFG" pass moves musttail call from tail
           Product: libraries
           Version: 5.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Transformation Utilities
          Assignee: unassignedbugs at nondot.org
          Reporter: benzrf at gmail.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 19611
  --> https://bugs.llvm.org/attachment.cgi?id=19611&action=edit
Files mentioned in the description

The attached file `musttail.ll` branches before making a call. The callee is
the same in both branches, but it is a non-tail call in one branch and a
`musttail` call in the other. The optimizer mistakenly merges the two calls
into a single one before the branch, resulting in incorrect output. Running
`clang -O1 -S -emit-llvm musttail.ll -o musttail_O1.ll` produces an attached
malformed file which is rejected by `llc` for containing a `musttail` call in
non-tail position. I have also attached the output of `opt -O1 -S
-print-after-all musttail.ll`.

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