Extended Description

Some testcases:

; RUN: llvm-upgrade < %s | llvm-as | llc -march=x86 | grep {jmp \*ecx}
declare int %putchar(int)

int %main(){
%f = cast int (int, int*, int)* %check_tail to int*
%res = tail call fastcc int %check_tail( int 10, int* %f,int 10)
ret int %res
}

fastcc int %check_tail(int %x, int* %f, int %g) {
%tmp1 = setgt int %x, 0
br bool %tmp1, label %if-then, label %if-else

if-then:
%fun_ptr = cast int* %f to int(int, int*, int)*
%arg1 = add int %x, -1
call int %putchar(int 90)
%res = tail call fastcc int %fun_ptr( int %arg1, int * %f, int %g)
ret int %res

if-else:
ret int %x
}

; RUN: llvm-upgrade < %s | llvm-as | llc -march=x86 -x86-asm-syntax=intel | not grep call
fastcc int %bar(int %X, int(double, int) *%FP) {
%Y = tail call fastcc int %FP(double 0.0, int %X)
ret int %Y
}