[LLVMbugs] [Bug 3694] New: missing instcombine for GEP 0, X, Y, Z of bitcast of Ty* to [ 0 x Ty]*

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=3694

           Summary: missing instcombine for GEP 0,X,Y,Z of bitcast of Ty* to
                    [0 x Ty]*
           Product: new-bugs
           Version: unspecified
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: baldrick at free.fr
                CC: llvmbugs at cs.uiuc.edu


test/FrontendC/2007-03-27-VarLengthArray.c now compiles to

define i32 @e(i32 %m, i32 %n) nounwind {
entry:
        %0 = alloca i32, i32 %n, align 4                ; <i32*> [#uses=2]
        %1 = bitcast i32* %0 to [0 x i32]*              ; <[0 x i32]*>
[#uses=1]
        call void @f(i32* %0) nounwind
        %2 = getelementptr [0 x i32]* %1, i32 0, i32 %m         ; <i32*>
[#uses=1]
        %3 = load i32* %2, align 4              ; <i32> [#uses=1]
        ret i32 %3
}

The bitcast could be eliminated by stripping the
first index off the GEP.


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