[LLVMbugs] [Bug 1949] New: instcombine doesn't fold away add/icmp ult

bugzilla-daemon at cs.uiuc.edu bugzilla-daemon at cs.uiuc.edu
Sat Jan 26 21:37:33 PST 2008


           Summary: instcombine doesn't fold away add/icmp ult
           Product: libraries
           Version: trunk
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: nicholas at mxc.ca
                CC: llvmbugs at cs.uiuc.edu

>From other optimizations, instcombine will produce this:

define i1 @f(i32 %a) {
  %a.off = add i32 %a, 4          ; <i32> [#uses=1]
  %C = icmp ult i32 %a.off, 4             ; <i1> [#uses=1]
  ret i1 %C

which is actually equivalent to:

define i1 @f(i32 %a) {
  %C = icmp ugt i32 %a.off, -5             ; <i1> [#uses=1]
  ret i1 %C

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