disable this instcombine xform, it miscompiles:

disable this instcombine xform, it miscompiles:

define i32 @main() {
entry:
	%z = alloca i32		; <i32*> [#uses=2]
	store i32 0, i32* %z
	%tmp = load i32* %z		; <i32> [#uses=1]
	%sub = sub i32 %tmp, 1		; <i32> [#uses=1]
	%cmp = icmp ult i32 %sub, 0		; <i1> [#uses=1]
	%retval = select i1 %cmp, i32 1, i32 0		; <i32> [#uses=1]
	ret i32 %retval
}

into ret 1, instead of ret 0.

Christopher, please investigate.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45383 91177308-0d34-0410-b5e6-96231b3b80d8