Convert kUseReadBarrier to static const from constexpr

This CL would compile both CC and userfaultfd GC in the art library,
enabling us to choose either of the two during boot time depending on
whether the device has userfaultfd kernel feature or not.

The CC GC is still chosen unless we use ART_USE_READ_BARRIER=false
during build time. This behavior will later be changed to choosing CC
*only* if ART_USE_READ_BARRIER=true is used. In other cases, if the
device has userfaultfd support then that GC will be chosen.

Bug: 160737021
Bug: 230021033
Test: art/test/testrunner/testrunner.py
Change-Id: I370f1a9f6b8cdff8c2ce3cf7aa936bccd7ed675f

1 files changed, 11 insertions, 10 deletions

diff --git a/build/art.go b/build/art.go
index c39b7e3f38..56df14239f 100644
--- a/build/art.go
+++ b/build/art.go
@@ -38,19 +38,13 @@ func globalFlags(ctx android.LoadHookContext) ([]string, []string) {
 	opt := ctx.Config().GetenvWithDefault("ART_NDEBUG_OPT_FLAG", "-O3")
 	cflags = append(cflags, opt)
 
-	tlab := false
-
-	gcType := ctx.Config().GetenvWithDefault("ART_DEFAULT_GC_TYPE", "CMS")
+	gcType := ctx.Config().GetenvWithDefault("ART_DEFAULT_GC_TYPE", "CMC")
 
 	if ctx.Config().IsEnvTrue("ART_TEST_DEBUG_GC") {
 		gcType = "SS"
-		tlab = true
 	}
 
 	cflags = append(cflags, "-DART_DEFAULT_GC_TYPE_IS_"+gcType)
-	if tlab {
-		cflags = append(cflags, "-DART_USE_TLAB=1")
-	}
 
 	if ctx.Config().IsEnvTrue("ART_HEAP_POISONING") {
 		cflags = append(cflags, "-DART_HEAP_POISONING=1")
@@ -70,11 +64,18 @@ func globalFlags(ctx android.LoadHookContext) ([]string, []string) {
 		asflags = append(asflags,
 			"-DART_USE_READ_BARRIER=1",
 			"-DART_READ_BARRIER_TYPE_IS_"+barrierType+"=1")
-	}
 
-	if !ctx.Config().IsEnvFalse("ART_USE_GENERATIONAL_CC") {
-		cflags = append(cflags, "-DART_USE_GENERATIONAL_CC=1")
+		if !ctx.Config().IsEnvFalse("ART_USE_GENERATIONAL_CC") {
+			cflags = append(cflags, "-DART_USE_GENERATIONAL_CC=1")
+		}
+		// For now force CC as we don't want to make userfaultfd GC the default.
+		// Eventually, make it such that we force CC only if ART_USE_READ_BARRIER
+		// was set to true explicitly during build time.
+		cflags = append(cflags, "-DART_FORCE_USE_READ_BARRIER=1")
 	}
+	// The only GC which does not want ART_USE_TLAB set is CMS, which isn't actually used.
+	// When read-barrier is not set, we use userfaultfd GC.
+	cflags = append(cflags, "-DART_USE_TLAB=1")
 
 	cdexLevel := ctx.Config().GetenvWithDefault("ART_DEFAULT_COMPACT_DEX_LEVEL", "fast")
 	cflags = append(cflags, "-DART_DEFAULT_COMPACT_DEX_LEVEL="+cdexLevel)