[LLVMbugs] [Bug 2655] New: memcpyopt doesn't zap an alloca + memmove

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=2655

           Summary: memcpyopt doesn't zap an alloca + memmove
           Product: libraries
           Version: 1.0
          Platform: PC
        OS/Version: All
            Status: NEW
          Keywords: code-quality
          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 this case, memcpyopt should "out->replaceAllUsesWith(agg.result)" and then
nuke the memmove as an identity memmove:

target datalayout =
"e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
target triple = "i686-pc-linux-gnu"
        %struct.out = type <{ i32, i32 }>

define void @foo(%struct.out* sret %agg.result) {
entry:
        %out = alloca %struct.out, align 4              ; <%struct.out*>
[#uses=3]
        %tmp = getelementptr %struct.out* %out, i32 0, i32 0            ;
<i32*> [#uses=1]
        %call = call i32 @bar( )                ; <i32> [#uses=1]
        store i32 %call, i32* %tmp
        %tmp1 = getelementptr %struct.out* %out, i32 0, i32 1           ;
<i32*> [#uses=1]
        %call2 = call i32 @bar( )               ; <i32> [#uses=1]
        store i32 %call2, i32* %tmp1
        %tmp3 = bitcast %struct.out* %agg.result to i8*         ; <i8*>
[#uses=1]
        %tmp4 = bitcast %struct.out* %out to i8*                ; <i8*>
[#uses=1]
        call void @llvm.memmove.i32( i8* %tmp3, i8* %tmp4, i32 8, i32 4 )
        ret void
}

declare void @llvm.memmove.i32(i8*, i8*, i32, i32) nounwind

declare i32 @bar()


This produces:

define void @foo(%struct.out* sret %agg.result) {
entry:
        %call = call i32 @bar( )                ; <i32> [#uses=1]
        %call2 = call i32 @bar( )               ; <i32> [#uses=1]
        %tmp3 = bitcast %struct.out* %agg.result to i8*         ; <i8*>
[#uses=0]
        %agg.result.0 = getelementptr %struct.out* %agg.result, i32 0, i32 0   
        ; <i32*> [#uses=1]
        store i32 %call, i32* %agg.result.0
        %agg.result.1 = getelementptr %struct.out* %agg.result, i32 0, i32 1   
        ; <i32*> [#uses=1]
        store i32 %call2, i32* %agg.result.1
        ret void
}


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