[LLVMbugs] [Bug 3198] New: GVN not eliminating fully redundant GEPs

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=3198

           Summary: GVN not eliminating fully redundant GEPs
           Product: libraries
           Version: 1.0
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: clattner at apple.com
                CC: resistor at mac.com, llvmbugs at cs.uiuc.edu


In the testcase test/Transforms/GVN/rle-must-alias.ll, if you disable load
elimination, you'll see that GVN produces:

bb:             ; preds = %entry
        %2 = tail call i32 (...)* @bar() nounwind               ; <i32>
[#uses=0]
        %3 = getelementptr [100 x i32]* @H, i32 0, i32 %i               ;
<i32*> [#uses=1]
        %4 = load i32* %3, align 4              ; <i32> [#uses=1]
        store i32 %4, i32* @G, align 4
        br label %bb3

bb1:            ; preds = %entry
        %5 = tail call i32 (...)* @baz() nounwind               ; <i32>
[#uses=0]
        %6 = getelementptr [100 x i32]* @H, i32 0, i32 %i               ;
<i32*> [#uses=1]
        %7 = load i32* %6, align 4              ; <i32> [#uses=2]
        store i32 %7, i32* @G, align 4
        %8 = icmp eq i32 %7, 0          ; <i1> [#uses=1]
        br i1 %8, label %bb3, label %bb4

bb3:            ; preds = %bb1, %bb
        %9 = getelementptr [100 x i32]* @H, i32 0, i32 %i               ;
<i32*> [#uses=1]

The %9 load is fully redundant with %3/%6.  I thought that GVN could handle
this case already?


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