cmd: use built-in clear for maps instead of range+delete

Now that we're bootstrapping from a toolchain that has the clear builtin.

Update #64751

Change-Id: Ia86d96c253c9f7c66131cd02048a493047569641
Reviewed-on: https://go-review.googlesource.com/c/go/+/610237
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>

src/cmd/compile/internal/inline/inlheur/scoring.go

@@ -569,9 +569,7 @@ func ScoreCallsCleanup() {
 			allCallSites[call] = cs
 		}
 	}
-	for k := range scoreCallsCache.tab {
-		delete(scoreCallsCache.tab, k)
-	}
+	clear(scoreCallsCache.tab)
 }
 
 // GetCallSiteScore returns the previously calculated score for call

src/cmd/compile/internal/liveness/mergelocals.go

@@ -489,8 +489,8 @@ func (cs *cstate) populateIndirectUseTable(cands []*ir.Name) ([]*ir.Name, []cand
 		rawcands[n] = struct{}{}
 	}
 	for k := 0; k < len(cs.f.Blocks); k++ {
-		genmapclear(pendingUses)
-		genmapclear(blockIndirectUE)
+		clear(pendingUses)
+		clear(blockIndirectUE)
 		b := cs.f.Blocks[k]
 		for _, v := range b.Values {
 			if n, e := affectedVar(v); n != nil {
@@ -546,7 +546,7 @@ func (cs *cstate) populateIndirectUseTable(cands []*ir.Name) ([]*ir.Name, []cand
 		// that value is flowing out of the block off somewhere else,
 		// we're going to treat that local as truly address-taken and
 		// not have it be a merge candidate.
-		genmapclear(evicted)
+		clear(evicted)
 		if len(pendingUses) != 0 {
 			for id, nc := range pendingUses {
 				if cs.trace > 2 {
@@ -605,14 +605,6 @@ func (cs *cstate) populateIndirectUseTable(cands []*ir.Name) ([]*ir.Name, []cand
 	return pruned, regions
 }
 
-// FIXME: bootstrap tool compiler is build with a "go 1.20" go.mod, so
-// we are not allowed to use map clear yet. Use this helper instead.
-func genmapclear[KT comparable, VT any](m map[KT]VT) {
-	for k := range m {
-		delete(m, k)
-	}
-}
-
 type nameCount struct {
 	n     *ir.Name
 	count int32

src/cmd/compile/internal/liveness/plive.go

@@ -168,15 +168,9 @@ func (m *Map) reset() {
 		m.UnsafeVals = make(map[ssa.ID]bool)
 		m.UnsafeBlocks = make(map[ssa.ID]bool)
 	} else {
-		for k := range m.Vals {
-			delete(m.Vals, k)
-		}
-		for k := range m.UnsafeVals {
-			delete(m.UnsafeVals, k)
-		}
-		for k := range m.UnsafeBlocks {
-			delete(m.UnsafeBlocks, k)
-		}
+		clear(m.Vals)
+		clear(m.UnsafeVals)
+		clear(m.UnsafeBlocks)
 	}
 	m.DeferReturn = objw.StackMapDontCare
 }

src/cmd/compile/internal/ssa/deadstore.go

@@ -29,10 +29,7 @@ func dse(f *Func) {
 		//  storeUse contains stores which are used by a subsequent store.
 		loadUse.clear()
 		storeUse.clear()
-		// TODO(deparker): use the 'clear' builtin once compiler bootstrap minimum version is raised to 1.21.
-		for k := range localAddrs {
-			delete(localAddrs, k)
-		}
+		clear(localAddrs)
 		stores = stores[:0]
 		for _, v := range b.Values {
 			if v.Op == OpPhi {

src/cmd/compile/internal/ssa/debug.go

@@ -588,9 +588,7 @@ func BuildFuncDebug(ctxt *obj.Link, f *Func, loggingLevel int, stackOffset func(
 	if state.varParts == nil {
 		state.varParts = make(map[*ir.Name][]SlotID)
 	} else {
-		for n := range state.varParts {
-			delete(state.varParts, n)
-		}
+		clear(state.varParts)
 	}
 
 	// Recompose any decomposed variables, and establish the canonical

src/cmd/compile/internal/ssa/regalloc.go

@@ -2228,13 +2228,9 @@ func (e *edgeState) setup(idx int, srcReg []endReg, dstReg []startReg, stacklive
 	}
 
 	// Clear state.
-	for _, vid := range e.cachedVals {
-		delete(e.cache, vid)
-	}
+	clear(e.cache)
 	e.cachedVals = e.cachedVals[:0]
-	for k := range e.contents {
-		delete(e.contents, k)
-	}
+	clear(e.contents)
 	e.usedRegs = 0
 	e.uniqueRegs = 0
 	e.finalRegs = 0

src/cmd/compile/internal/ssagen/ssa.go

@@ -991,9 +991,7 @@ func (s *state) startBlock(b *ssa.Block) {
 	}
 	s.curBlock = b
 	s.vars = map[ir.Node]*ssa.Value{}
-	for n := range s.fwdVars {
-		delete(s.fwdVars, n)
-	}
+	clear(s.fwdVars)
 }
 
 // endBlock marks the end of generating code for the current block.