Switch to clang-r407598 (12.0.1).

Also suppress a clang-tidy warning and a ubsan check to pass compilation.

Bug: 171348143
Test: build.
Change-Id: Ie5162c15df172cefd7cff9776e54531fd620bc23

cc/config/clang.go

@@ -94,6 +94,7 @@ var ClangLibToolingUnknownCflags = sorted([]string{})
 // `modernize-*`.
 var ClangTidyDisableChecks = []string{
 	"misc-no-recursion",
+	"readability-function-cognitive-complexity", // http://b/175055536
 }
 
 func init() {
@@ -190,6 +191,8 @@ func init() {
 		"-Wno-pessimizing-move",                     // http://b/154270751
 		// New warnings to be fixed after clang-r399163
 		"-Wno-non-c-typedef-for-linkage", // http://b/161304145
+		// New warnings to be fixed after clang-r407598
+		"-Wno-string-concatenation", // http://b/175068488
 	}, " "))
 
 	// Extra cflags for external third-party projects to disable warnings that

cc/config/global.go

@@ -135,8 +135,8 @@ var (
 
 	// prebuilts/clang default settings.
 	ClangDefaultBase         = "prebuilts/clang/host"
-	ClangDefaultVersion      = "clang-r399163b"
+	ClangDefaultVersion      = "clang-r407598"
-	ClangDefaultShortVersion = "11.0.5"
+	ClangDefaultShortVersion = "12.0.1"
 
 	// Directories with warnings from Android.bp files.
 	WarningAllowedProjects = []string{

cc/sanitize.go

@@ -458,6 +458,22 @@ func toDisableImplicitIntegerChange(flags []string) bool {
 	return false
 }
 
+func toDisableUnsignedShiftBaseChange(flags []string) bool {
+	// Returns true if any flag is fsanitize*integer, and there is
+	// no explicit flag about sanitize=unsigned-shift-base.
+	for _, f := range flags {
+		if strings.Contains(f, "sanitize=unsigned-shift-base") {
+			return false
+		}
+	}
+	for _, f := range flags {
+		if strings.HasPrefix(f, "-fsanitize") && strings.Contains(f, "integer") {
+			return true
+		}
+	}
+	return false
+}
+
 func (sanitize *sanitize) flags(ctx ModuleContext, flags Flags) Flags {
 	minimalRuntimeLib := config.UndefinedBehaviorSanitizerMinimalRuntimeLibrary(ctx.toolchain()) + ".a"
 	minimalRuntimePath := "${config.ClangAsanLibDir}/" + minimalRuntimeLib
@@ -614,6 +630,10 @@ func (sanitize *sanitize) flags(ctx ModuleContext, flags Flags) Flags {
 		if toDisableImplicitIntegerChange(flags.Local.CFlags) {
 			flags.Local.CFlags = append(flags.Local.CFlags, "-fno-sanitize=implicit-integer-sign-change")
 		}
+		// http://b/171275751, Android doesn't build with this sanitizer yet.
+		if toDisableUnsignedShiftBaseChange(flags.Local.CFlags) {
+			flags.Local.CFlags = append(flags.Local.CFlags, "-fno-sanitize=unsigned-shift-base")
+		}
 	}
 
 	if len(sanitize.Properties.DiagSanitizers) > 0 {