[LLVMbugs] [Bug 2659] New: redundant movl generated on x86

bugzilla-daemon at cs.uiuc.edu bugzilla-daemon at cs.uiuc.edu
Sun Aug 10 02:13:11 PDT 2008


           Summary: redundant movl generated on x86
           Product: new-bugs
           Version: unspecified
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: ianh at berkeley.edu
                CC: llvmbugs at cs.uiuc.edu

I compiled the attached .ll file to x86 assembly and found something odd. 
Namely, in the inner loop: 

LBB1_3: ## forbody
  imull %ecx, %eax
  xorl  %edx, %edx
  divl  %edi
  decl  %ecx
  incl  %edi
  cmpl  %esi, %edi
  movl  %eax, %edx
  movl  %edx, %eax
  jbe LBB1_3  ## forbody
  jmp LBB1_5  ## afterfor

It moves %eax into %edx... then moves it right back again!

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