[LLVMbugs] [Bug 2265] New: Can't solve trip count for simple loop

bugzilla-daemon at cs.uiuc.edu bugzilla-daemon at cs.uiuc.edu
Wed Apr 30 00:27:59 PDT 2008


           Summary: Can't solve trip count for simple loop
           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: resistor at mac.com
                CC: llvmbugs at cs.uiuc.edu

Here's a pretty simple loop:

define i32 @"test function"(i32 %i0, i32 %j0) {
        br label %BB2

BB2:            ; preds = %BB5, %BB1
        %k2 = phi i32 [ 0, %BB1 ], [ %k3, %BB5 ]                ; <i32>
        %kcond = icmp slt i32 %k2, 100          ; <i1> [#uses=1]
        br i1 %kcond, label %BB5, label %BB4

BB4:            ; preds = %BB2
        ret i32 1

BB5:            ; preds = %BB2
        %k3 = add i32 %k2, 1            ; <i32> [#uses=1]
        br label %BB2

The {BB2, BB5} loop has an obvious trip count of 100, Loop::getTripCount fails
to realize this.  This is blocking loop deletion from removing the loop.

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