[LLVMbugs] [Bug 5146] New: Low perf compared to gcc for benchmark

bugzilla-daemon at cs.uiuc.edu bugzilla-daemon at cs.uiuc.edu
Wed Oct 7 05:42:10 PDT 2009


           Summary: Low perf compared to gcc for benchmark
           Product: libraries
           Version: 2.6
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: alenhar2 at uiuc.edu
                CC: llvmbugs at cs.uiuc.edu

Created an attachment (id=3618)
 --> (http://llvm.org/bugs/attachment.cgi?id=3618)

Filed on behalf of bearophile:

See beginning of C file for bearophile's 2.5 timings.  I get with llvm 2.6 and
gcc 4.3.4 at his compile options with -fno-math-errno
-funsafe-math-optimizations: 2.7 sec and 2.1 sec respectively (Intel Q6600), so
what ever is the problem hasn't gone completely away in 2.6.

Some potential items from a quick glance through the asm:

tfo_apply has more mmx adds than the gcc one
atan2 (maybe others) are tail calls in gcc but not llvm

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