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.

llvm-svn: 45383

llvm/lib/Transforms/Scalar/InstructionCombining.cpp

@@ -4835,9 +4835,11 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
   if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
       Value *A, *B;
     
+#if 0
     // (icmp cond (sub A B) 0) -> (icmp cond A B)
     if (CI->isNullValue() && match(Op0, m_Sub(m_Value(A), m_Value(B))))
       return new ICmpInst(I.getPredicate(), A, B);
+#endif
     
     switch (I.getPredicate()) {
     default: break;