[LLVMbugs] [Bug 9939] New: Loop strength reduction breaks this test

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue May 17 18:03:41 PDT 2011


           Summary: Loop strength reduction breaks this test
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Common Code Generator Code
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: rafael.espindola at gmail.com
                CC: llvmbugs at cs.uiuc.edu

Created an attachment (id=6604)
 --> (http://llvm.org/bugs/attachment.cgi?id=6604)

Loop strength reduction is breaking firefox's test_jsctypes.js.

I reduced the problem to the attached testcase, but haven't been able to find
the bug itself yet. Looks like what it gets wrong is the compensation added
when the loop condition is converted from 

        cmpq    %r9, %rdx
        jne     .LBB0_4

        addq    $-2, %rcx
        jne     .LBB0_4

I checked that building with " -Xclang -mllvm -Xclang -disable-lsr" added
causes the original test to pass.

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