[LLVMbugs] [Bug 7868] New: major missed optimizations

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue Aug 10 16:16:25 PDT 2010


           Summary: major missed optimizations
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: rwgk at yahoo.com
                CC: llvmbugs at cs.uiuc.edu

Created an attachment (id=5361)
 --> (http://llvm.org/bugs/attachment.cgi?id=5361)
reduced test case

Per request of Douglas Gregor and Chris Lattner, attached is reduced C++ code
to demonstrate major missed optimizations.
(The original code is from LAPACK 3.2.1, automatically converted to C++.)

clang version 2.8 (trunk 108205)
clang++ -O3 -ffast-math reduced_dlasr.cpp
% time a.out
1.118u 0.005s 0:01.12 99.1%     0+0k 0+0io 0pf+0w

g++ (GCC) 4.4.4 20100630 (Red Hat 4.4.4-10)
g++ -O3 -ffast-math reduced_dlasr.cpp
% time a.out
0.316u 0.005s 0:00.32 96.8%     0+0k 0+0io 0pf+0w

See also:
cfe-dev at cs.uiuc.edu thread "food for optimizer developers"
started 8/9/2010.

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