[llvm-bugs] [Bug 32398] New: std::exp() produces infinite loop on Windows with -Ofast

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=32398

            Bug ID: 32398
           Summary: std::exp() produces infinite loop on Windows with
                    -Ofast
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Windows XP
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: techmeology at techmeology.co.uk
                CC: llvm-bugs at lists.llvm.org

Created attachment 18159
  --> https://bugs.llvm.org/attachment.cgi?id=18159&action=edit
Demonstration of the bug

When cross compiling for Windows (I haven't tested native compile on Windows),
std::exp() is miscompiled as an infinite loop if -Ofast is used. exp() works
correctly, and std::exp() works correctly on Linux.

Clang version: 297935 (Also tried a 4.0.0 pre-release with similar results)
OS: Arch Linux

Steps to reproduce: see build.sh in the tarball

Expected result: No infinite loop should be produced.
Actual result: The produced IR has a branch to a branch to itself (i.e: an
infinite loop).

Contents of the tarball:
build.sh
    Shows how I produced all the files in the out directory.
exp.cpp
    A minimal reproducer that demonstrates the bug.
out/windows_ofast/exp_expanded.cpp
    The preprocessed version of exp.cpp on my system for -Ofast on Windows
out/windows_ofast/exp.bc
    The generated IR bitcode for exp.cpp

The remaining files are analogous for -O3 and for native build.

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