v.Pos = v.Pos.WithNotStmt()
						}
						// This is a redundant explicit nil check.
						v.reset(OpConstBool)
						v.AuxInt = 1 // true
					}
				case OpNilCheck:
					ptr := v.Args[0]
					if nilCheck := nonNilValues[ptr.ID]; nilCheck != nil {
						// This is a redundant implicit nil check.
						// Logging in the style of the former compiler -- and omit line 1,
						// which is usually in generated code.

// otherwise v is ordered before s.
// Specifically, values are ordered like
//
//	store1
//	NilCheck that depends on store1
//	other values that depends on store1
//	store2
//	NilCheck that depends on store2
//	other values that depends on store2
//	...
//
// The order of non-store and non-NilCheck values are undefined
// (not necessarily dependency order). This should be cheaper

		if b == fun.blocks["secondCheck"] && isNilCheck(b) {
			t.Errorf("secondCheck was not eliminated")
		}
		if b == fun.blocks["differentCheck"] && isNilCheck(b) {
			foundDifferentCheck = true
		}
	}
	if !foundDifferentCheck {
		t.Errorf("removed differentCheck, but shouldn't have")
	}
}

// TestNilcheckInFalseBranch tests that nil checks in the false branch of a nilcheck
// block are *not* removed.

				}
			case OpNilCheck:
				// nil checks have pointer type before scheduling, and
				// void type after scheduling.
				if f.scheduled {
					if v.Uses != 0 {
						f.Fatalf("nilcheck must have 0 uses %s", v.Uses)
					}
					if !v.Type.IsVoid() {
						f.Fatalf("nilcheck must have void type %s", v.Type.String())
					}
				} else {

	// checkLower must run after lowering & subsequent dead code elim
	{"lower", "checkLower"},
	{"lowered deadcode", "checkLower"},
	{"late lower", "checkLower"},
	// late nilcheck needs instructions to be scheduled.
	{"schedule", "late nilcheck"},
	// flagalloc needs instructions to be scheduled.
	{"schedule", "flagalloc"},
	// regalloc needs flags to be allocated first.
	{"flagalloc", "regalloc"},

	// and the offset is small enough that if x is nil, the address will still be
	// in the first unmapped page of memory.

	_ = x[9] // ERROR "generated nil check" // bug: would like to remove this check (but nilcheck and load are in different blocks)

	for {
		if x[9] != 0 { // ERROR "removed nil check"
			break
		}
	}

	x = fx10()

			Valu("mem", OpInitMem, types.TypeMem, 0, nil),
			Valu("c1", OpArg, c.config.Types.Bool, 0, nil),
			Valu("p", OpArg, c.config.Types.IntPtr, 0, nil),
			If("c1", "z0", "exit")),
		Bloc("z0",
			Valu("nilcheck", OpNilCheck, c.config.Types.IntPtr, 0, nil, "p", "mem"),
			Goto("exit")),
		Bloc("exit",
			Exit("mem"),
		))
	CheckFunc(fun.f)
	fuseLate(fun.f)
	z0, ok := fun.blocks["z0"]
	if !ok || z0.Kind == BlockInvalid {

// license that can be found in the LICENSE file.

package ssa

import (
	"cmd/internal/src"
	"fmt"
	"sort"
)

func isPoorStatementOp(op Op) bool {
	switch op {
	// Note that Nilcheck often vanishes, but when it doesn't, you'd love to start the statement there
	// so that a debugger-user sees the stop before the panic, and can examine the value.

// There may be false positives.
func isEmpty(b *Block) bool {
	for _, v := range b.Values {
		if v.Uses > 0 || v.Op.IsCall() || v.Op.HasSideEffects() || v.Type.IsVoid() || opcodeTable[v.Op].nilCheck {
			return false
		}
	}
	return true
}

// fuseBlockPlain handles a run of blocks with length >= 2,
// whose interior has single predecessors and successors,

					liveOrderStmts = append(liveOrderStmts, v)
				}
			}
		}
		for _, v := range b.Values {
			if (opcodeTable[v.Op].call || opcodeTable[v.Op].hasSideEffects || opcodeTable[v.Op].nilCheck) && !live[v.ID] {
				live[v.ID] = true
				q = append(q, v)
				if v.Pos.IsStmt() != src.PosNotStmt {
					liveOrderStmts = append(liveOrderStmts, v)
				}
			}
			if v.Op == OpInlMark {