const minZeroPage = 4096

// faultOnLoad is true if a load to an address below minZeroPage will trigger a SIGSEGV.
var faultOnLoad = buildcfg.GOOS != "aix"

// nilcheckelim2 eliminates unnecessary nil checks.
// Runs after lowering and scheduling.
func nilcheckelim2(f *Func) {
	unnecessary := f.newSparseMap(f.NumValues()) // map from pointer that will be dereferenced to index of dereferencing value in b.Values[]

	{"generic cse", "dse"},
	// cse substantially improves nilcheckelim efficacy
	{"generic cse", "nilcheckelim"},
	// allow deadcode to clean up after nilcheckelim
	{"nilcheckelim", "generic deadcode"},
	// nilcheckelim generates sequences of plain basic blocks
	{"nilcheckelim", "late fuse"},
	// nilcheckelim relies on opt to rewrite user nil checks
	{"opt", "nilcheckelim"},

	opt(fun.f)
	nilcheckelim(fun.f)

	// clean up the removed nil check
	fuse(fun.f, fuseTypePlain)
	deadcode(fun.f)

	CheckFunc(fun.f)
	for _, b := range fun.f.Blocks {
		if b == fun.blocks["secondCheck"] && isNilCheck(b) {
			t.Errorf("secondCheck was not eliminated")
		}
	}
}

// TestNilcheckBug reproduces a bug in nilcheckelim found by compiling math/big

				continue
			}
			sset.add(v.MemoryArg().ID) // record that v's memory arg is used
		}
		if v.Op == OpNilCheck {
			hasNilCheck = true
		}
	}
	if len(stores) == 0 || !hasNilCheck && f.pass.name == "nilcheckelim" {
		// there is no store, the order does not matter
		return values
	}

	// find last store, which is the one that is not used by other stores
	var last *Value
	for _, v := range stores {