cmd/compile/internal: refactor coverage ir.Name flags

Minor refactoring to eliminate one of the ir.Name flag values used
when building in coverage mode (no changes to functionality). This is
intended to free up a bit in the uint16 flags field to be used in a
subsequent patch.

Change-Id: I4aedb9a55fde24c808ff3f7b077ee0552aa979af
Reviewed-on: https://go-review.googlesource.com/c/go/+/572055
Reviewed-by: Cherry Mui <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: thanm

src/cmd/compile/internal/coverage/cover.go

@@ -75,7 +75,7 @@ func Fixup() {
 		}
 		if strings.HasPrefix(s.Name, counterPrefix) {
 			ckTypSanity(nm, "countervar")
-			nm.SetCoverageCounter(true)
+			nm.SetCoverageAuxVar(true)
 			s := nm.Linksym()
 			s.Type = objabi.SCOVERAGE_COUNTER
 		}

src/cmd/compile/internal/gc/obj.go

@@ -154,7 +154,7 @@ func dumpGlobal(n *ir.Name) {
 	}
 	types.CalcSize(n.Type())
 	ggloblnod(n)
-	if n.CoverageCounter() || n.CoverageAuxVar() || n.Linksym().Static() {
+	if n.CoverageAuxVar() || n.Linksym().Static() {
 		return
 	}
 	base.Ctxt.DwarfGlobal(types.TypeSymName(n.Type()), n.Linksym())
@@ -253,6 +253,11 @@ func ggloblnod(nam *ir.Name) {
 	linkname := nam.Sym().Linkname
 	name := nam.Sym().Name
 
+	var saveType objabi.SymKind
+	if nam.CoverageAuxVar() {
+		saveType = s.Type
+	}
+
 	// We've skipped linkname'd globals's instrument, so we can skip them here as well.
 	if base.Flag.ASan && linkname == "" && pkginit.InstrumentGlobalsMap[name] != nil {
 		// Write the new size of instrumented global variables that have
@@ -266,8 +271,9 @@ func ggloblnod(nam *ir.Name) {
 	if nam.Libfuzzer8BitCounter() {
 		s.Type = objabi.SLIBFUZZER_8BIT_COUNTER
 	}
-	if nam.CoverageCounter() {
-		s.Type = objabi.SCOVERAGE_COUNTER
+	if nam.CoverageAuxVar() && saveType == objabi.SCOVERAGE_COUNTER {
+		// restore specialized counter type (which Globl call above overwrote)
+		s.Type = saveType
 	}
 	if nam.Sym().Linkname != "" {
 		// Make sure linkname'd symbol is non-package. When a symbol is

src/cmd/compile/internal/inline/inl.go

@@ -1162,7 +1162,10 @@ func isIndexingCoverageCounter(n ir.Node) bool {
 		return false
 	}
 	nn := ixn.X.(*ir.Name)
-	return nn.CoverageCounter()
+	// CoverageAuxVar implies either a coverage counter or a package
+	// ID; since the cover tool never emits code to index into ID vars
+	// this is effectively testing whether nn is a coverage counter.
+	return nn.CoverageAuxVar()
 }
 
 // isAtomicCoverageCounterUpdate examines the specified node to

src/cmd/compile/internal/ir/name.go

@@ -192,8 +192,7 @@ const (
 	nameInlLocal                 // PAUTO created by inliner, derived from callee local
 	nameOpenDeferSlot            // if temporary var storing info for open-coded defers
 	nameLibfuzzer8BitCounter     // if PEXTERN should be assigned to __sancov_cntrs section
-	nameCoverageCounter          // instrumentation counter var for cmd/cover
-	nameCoverageAuxVar           // instrumentation pkg ID variable cmd/cover
+	nameCoverageAuxVar           // instrumentation counter var or pkg ID for cmd/cover
 	nameAlias                    // is type name an alias
 )
 
@@ -209,7 +208,6 @@ func (n *Name) InlFormal() bool                { return n.flags&nameInlFormal !=
 func (n *Name) InlLocal() bool                 { return n.flags&nameInlLocal != 0 }
 func (n *Name) OpenDeferSlot() bool            { return n.flags&nameOpenDeferSlot != 0 }
 func (n *Name) Libfuzzer8BitCounter() bool     { return n.flags&nameLibfuzzer8BitCounter != 0 }
-func (n *Name) CoverageCounter() bool          { return n.flags&nameCoverageCounter != 0 }
 func (n *Name) CoverageAuxVar() bool           { return n.flags&nameCoverageAuxVar != 0 }
 
 func (n *Name) setReadonly(b bool)                 { n.flags.set(nameReadonly, b) }
@@ -224,7 +222,6 @@ func (n *Name) SetInlFormal(b bool)                { n.flags.set(nameInlFormal,
 func (n *Name) SetInlLocal(b bool)                 { n.flags.set(nameInlLocal, b) }
 func (n *Name) SetOpenDeferSlot(b bool)            { n.flags.set(nameOpenDeferSlot, b) }
 func (n *Name) SetLibfuzzer8BitCounter(b bool)     { n.flags.set(nameLibfuzzer8BitCounter, b) }
-func (n *Name) SetCoverageCounter(b bool)          { n.flags.set(nameCoverageCounter, b) }
 func (n *Name) SetCoverageAuxVar(b bool)           { n.flags.set(nameCoverageAuxVar, b) }
 
 // OnStack reports whether variable n may reside on the stack.