[LLVMbugs] [Bug 1810] New: Scalar evolution incorrectly handles Or instruction

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=1810

           Summary: Scalar evolution incorrectly handles Or instruction
           Product: new-bugs
           Version: unspecified
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: miscompilation
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: wmatyjewicz at fastmail.fm
                CC: llvmbugs at cs.uiuc.edu


Given the following code:

define void @fun() {
entry:
        br label %header
header:
        %i = phi i32 [ 1, %entry ], [ %i.next, %body ]
        %cond = icmp eq i32 %i, 10
        br i1 %cond, label %exit, label %body
body:
        %a = mul i32 %i, 5
        %b = or i32 %a, 1
        %i.next = add i32 %i, 1
        br label %header
exit:        
        ret void
}

scalar evolution pass (opt -analyze -scalar-evolution) produces incorrect chrec
for %b:
  %a = mul i32 %i, 5   
--> { 5,+, 5}<header>
  %b = or i32 %a, 1
--> { 6,+, 5}<header>
It is incorrect, because at the first iteration %b should be assigned 5, not 6.


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