[LLVMbugs] [Bug 12760] New: ARM: wrong pattern for SMMLS instruction

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Mon May 7 19:14:48 PDT 2012


             Bug #: 12760
           Summary: ARM: wrong pattern for SMMLS instruction
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: ARM
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: mans at mansr.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

The SMMLS instruction pattern is wrong, matching code of the form

  a - ((b * c) >> 32)

while the instruction actually performs the operation

  ((a << 32) - b * c) >> 32

This means incorrect code is generated in some cases.

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