[LLVMbugs] [Bug 1722] New: -indvars does not rewrite the exit condition for a two-level loop nest

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=1722

           Summary: -indvars does not rewrite the exit condition for a two-
                    level loop nest
           Product: libraries
           Version: 2.1
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Loop Optimizer
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: zhiruz at gmail.com
                CC: llvmbugs at cs.uiuc.edu


Created an attachment (id=1151)
 --> (http://llvm.org/bugs/attachment.cgi?id=1151)
foo.bc

//////// C code ////////////////
void foo()
{
    int i, j;
    for (i = 0; i < 100; ++i)
        for (j = 0; j < i; ++j)
            a[i][j] = i * j;
}

;;;;;;;;;;;;;;;;; ll code piece for the loop nest ;;;;;;;;;;;;;;;;;;;;;;

bb1:            ; preds = %bb10
        %tmp5 = mul i32 %i.0, %j.1              ; <i32> [#uses=1]
        %tmp7 = getelementptr [100 x [100 x i32]]* @a, i32 0, i32 %i.0, i32
%j.1                ; <i32*> [#uses=1]
        store i32 %tmp5, i32* %tmp7, align 4
        %tmp9 = add i32 %j.1, 1         ; <i32> [#uses=1]
        br label %bb10

bb10:           ; preds = %bb18, %bb1
        %j.1 = phi i32 [ %tmp9, %bb1 ], [ 0, %bb18 ]            ; <i32>
[#uses=4]
        %tmp13 = icmp slt i32 %j.1, %i.0                ; <i1> [#uses=1]
        br i1 %tmp13, label %bb1, label %bb15

bb15:           ; preds = %bb10
        %tmp17 = add i32 %i.0, 1                ; <i32> [#uses=1]
        br label %bb18

bb18:           ; preds = %bb15, %entry
        %i.0 = phi i32 [ 0, %entry ], [ %tmp17, %bb15 ]         ; <i32>
[#uses=5]
        %tmp20 = icmp slt i32 %i.0, 100         ; <i1> [#uses=1]
        br i1 %tmp20, label %bb10, label %return

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

After "opt -indvars -simplifycfg", 

;;;;;;;;;;;;;;;;; ll code piece after -indvars ;;;;;;;;;;;;;;;;;;;;;;
bb1:            ; preds = %bb10
        %tmp5 = mul i32 %i.0, %j.1              ; <i32> [#uses=1]
        %tmp7 = getelementptr [100 x [100 x i32]]* @a, i32 0, i32 %i.0, i32
%j.1                ; <i32*> [#uses=1]
        store i32 %tmp5, i32* %tmp7, align 4
        %indvar.next = add i32 %j.1, 1          ; <i32> [#uses=1]
        br label %bb10

bb10:           ; preds = %bb18, %bb1
        %j.1 = phi i32 [ %indvar.next, %bb1 ], [ 0, %bb18 ]             ; <i32>
[#uses=4]
        %tmp13 = icmp slt i32 %j.1, %i.0                ; <i1> [#uses=1]
        br i1 %tmp13, label %bb1, label %bb15

bb15:           ; preds = %bb10
        %indvar.next1 = add i32 %i.0, 1         ; <i32> [#uses=1]
        br label %bb18

bb18:           ; preds = %bb15, %entry
        %i.0 = phi i32 [ 0, %entry ], [ %indvar.next1, %bb15 ]          ; <i32>
[#uses=5]
        %exitcond = icmp ne i32 %i.0, 100               ; <i1> [#uses=1]
        br i1 %exitcond, label %bb10, label %return
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

I was hoping that the exit condition of the inner loop "%tmp13 = icmp slt i32
%j.1, %i.0" would be turned into "%tmp13 = icmp ne i32 %j.1, %i.0".
But this didnt happen. 

I didnt use tail duplicate and loop rotate to get the first bitcode (attached
as foo.bc). So my loop is in a bad form?


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