implement a todo: pass a eight-byte that consists of a

implement a todo: pass a eight-byte that consists of a
small integer + padding as that small integer.  On code
like:

struct c { double x; int y; };
void bar(struct c C) { }

This means that we compile to:

define void @bar(double %C.coerce0, i32 %C.coerce1) nounwind {
entry:
  %C = alloca %struct.c, align 8                  ; <%struct.c*> [#uses=2]
  %0 = getelementptr %struct.c* %C, i32 0, i32 0  ; <double*> [#uses=1]
  store double %C.coerce0, double* %0
  %1 = getelementptr %struct.c* %C, i32 0, i32 1  ; <i32*> [#uses=1]
  store i32 %C.coerce1, i32* %1

instead of:

define void @bar(double %C.coerce0, i64 %C.coerce1) nounwind {
entry:
  %C = alloca %struct.c, align 8                  ; <%struct.c*> [#uses=3]
  %0 = bitcast %struct.c* %C to %0*               ; <%0*> [#uses=2]
  %1 = getelementptr %0* %0, i32 0, i32 0         ; <double*> [#uses=1]
  store double %C.coerce0, double* %1
  %2 = getelementptr %0* %0, i32 0, i32 1         ; <i64*> [#uses=1]
  store i64 %C.coerce1, i64* %2

which gives SRoA heartburn.

This implements rdar://5711709, a nice low number :)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@109737 91177308-0d34-0410-b5e6-96231b3b80d8