[LLVMbugs] [Bug 1345] NEW: instcombine should recover more type info

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=1345

           Summary: instcombine should recover more type info
           Product: libraries
           Version: trunk
          Platform: Macintosh
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: sabre at nondot.org


Instcombine should eliminate the two bitcasts in this example:

define i8* @test(i8* %v) {
        %A = alloca [4 x i8*], align 16         ; <[4 x i8*]*> [#uses=3]
        %B = getelementptr [4 x i8*]* %A, i32 0, i32 0          ; <i8**> [#uses=1]
        store i8* null, i8** %B
        %C = bitcast [4 x i8*]* %A to { [16 x i8] }*            ; <{ [16 x i8] }*> [#uses=1]
        %D = getelementptr { [16 x i8] }* %C, i32 0, i32 0, i32 8               ; <i8*> [#uses=1]
        %E = bitcast i8* %D to i8**             ; <i8**> [#uses=1]
        store i8* %v, i8** %E
        %F = getelementptr [4 x i8*]* %A, i32 0, i32 2          ; <i8**> [#uses=1]
        %G = load i8** %F               ; <i8*> [#uses=1]
        ret i8* %G
}

Doing so would allow SROA to eliminate the alloca, turning the function into an identity function.

-Chris



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