Fold constant adds into loads and stores to frame indices.

For the following code:
double %ext(int %A.0__, long %A.1__) {
        %A_addr = alloca %typedef.DComplex              ; <%typedef.DComplex*> [#uses=2]
        %tmp.1 = cast %typedef.DComplex* %A_addr to int*                ; <int*> [#uses=1]
        store int %A.0__, int* %tmp.1
        %tmp.2 = getelementptr %typedef.DComplex* %A_addr, int 0, uint 1                ; <double*> [#uses=2]
        %tmp.3 = cast double* %tmp.2 to long*           ; <long*> [#uses=1]
        store long %A.1__, long* %tmp.3
        %tmp.5 = load double* %tmp.2            ; <double> [#uses=1]
        ret double %tmp.5
}

We now generate:
_ext:
.LBB_ext_0:     ;
        stw r3, -12(r1)
        stw r4, -8(r1)
        stw r5, -4(r1)
        lfd f1, -8(r1)
        blr

Instead of:
_ext:
.LBB_ext_0:     ;
        stw r3, -12(r1)
        addi r2, r1, -12
        stw r4, 4(r2)
        stw r5, 8(r2)
        lfd f1, 4(r2)
        blr

This also fires hundreds of times on MultiSource.

llvm-svn: 22533