[LLVMbugs] [Bug 21470] New: Clang miscompiles fabs on x86_64-w64-windows-gnu

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=21470

            Bug ID: 21470
           Summary: Clang miscompiles fabs on x86_64-w64-windows-gnu
           Product: clang
           Version: 3.5
          Hardware: PC
                OS: other
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: szabo.antal.92 at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 13283
  --> http://llvm.org/bugs/attachment.cgi?id=13283&action=edit
Test case

Clang miscompiles fabs on windows x64 using -O1 or greater, if it's parameter
is passed by reference to another function. Instead of the correct value, it
always returns 0. I couldn't reproduce the bug by separately optimizing with
opt, but using "clang -O1 -mllvm -print-before-all -mllvm -print-after-all
bug.cpp" I found that the "Interprocedural Sparse Conditional Constant
Propagation" pass is probably the cause; it replaces the correct return value
in @fabs with an undef ( see https://gist.github.com/Sh4rK/4ec63273c387f9978799
). Test case attached.

Clang version:
Downloaded from the MSYS2 project with pacman, package
"mingw64/mingw-w64-x86_64-clang" version 3.5.0-5 ( MSYS2 installation
instructions: http://sourceforge.net/p/msys2/wiki/MSYS2%20installation/ )

clang -v
clang version 3.5.0 (tags/RELEASE_350/final)
Target: x86_64-w64-windows-gnu
Thread model: posix

OS: Windows 8 x64

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