all: explode GOEXPERIMENT=regabi into 5 sub-experiments

This separates GOEXPERIMENT=regabi into five sub-experiments:
regabiwrappers, regabig, regabireflect, regabidefer, and regabiargs.
Setting GOEXPERIMENT=regabi now implies the working subset of these
(currently, regabiwrappers, regabig, and regabireflect).

This simplifies testing, helps derisk the register ABI project,
and will also help with performance comparisons.

This replaces the -abiwrap flag to the compiler and linker with
the regabiwrappers experiment.

As part of this, regabiargs now enables registers for all calls
in the compiler. Previously, this was statically disabled in
regabiEnabledForAllCompilation, but now that we can control it
independently, this isn't necessary.

For #40724.

Change-Id: I5171e60cda6789031f2ef034cc2e7c5d62459122
Reviewed-on: https://go-review.googlesource.com/c/go/+/302070
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>

1 files changed, 62 insertions, 3 deletions

diff --git a/src/cmd/internal/objabi/util.go b/src/cmd/internal/objabi/util.go
index 8c96ceca35..548e9d0a30 100644
--- a/src/cmd/internal/objabi/util.go
+++ b/src/cmd/internal/objabi/util.go
@@ -146,7 +146,28 @@ func init() {
 
 	// regabi is only supported on amd64.
 	if GOARCH != "amd64" {
-		Regabi_enabled = 0
+		Experiment.regabi = false
+		Experiment.RegabiWrappers = false
+		Experiment.RegabiG = false
+		Experiment.RegabiReflect = false
+		Experiment.RegabiDefer = false
+		Experiment.RegabiArgs = false
+	}
+	// Setting regabi sets working sub-experiments.
+	if Experiment.regabi {
+		Experiment.RegabiWrappers = true
+		Experiment.RegabiG = true
+		Experiment.RegabiReflect = true
+		// Not ready yet:
+		//Experiment.RegabiDefer = true
+		//Experiment.RegabiArgs = true
+	}
+	// Check regabi dependencies.
+	if Experiment.RegabiG && !Experiment.RegabiWrappers {
+		panic("GOEXPERIMENT regabig requires regabiwrappers")
+	}
+	if Experiment.RegabiArgs && !(Experiment.RegabiWrappers && Experiment.RegabiReflect && Experiment.RegabiDefer) {
+		panic("GOEXPERIMENT regabiargs requires regabiwrappers,regabireflect,regabidefer")
 	}
 
 	// Set GOEXPERIMENT to the parsed and canonicalized set of experiments.
@@ -186,9 +207,42 @@ var (
 	Fieldtrack_enabled        int
 	Preemptibleloops_enabled  int
 	Staticlockranking_enabled int
-	Regabi_enabled            int
 )
 
+// Experiment contains flags for GOEXPERIMENTs.
+//
+// TODO(austin): Move the package-level experiment flags into this.
+var Experiment ExpFlags
+
+type ExpFlags struct {
+	// regabi is split into several sub-experiments that can be
+	// enabled individually. GOEXPERIMENT=regabi implies the
+	// subset that are currently "working". Not all combinations work.
+	regabi bool
+	// RegabiWrappers enables ABI wrappers for calling between
+	// ABI0 and ABIInternal functions. Without this, the ABIs are
+	// assumed to be identical so cross-ABI calls are direct.
+	RegabiWrappers bool
+	// RegabiG enables dedicated G and zero registers in
+	// ABIInternal.
+	//
+	// Requires wrappers because it makes the ABIs incompatible.
+	RegabiG bool
+	// RegabiReflect enables the register-passing paths in
+	// reflection calls. This is also gated by intArgRegs in
+	// reflect and runtime (which are disabled by default) so it
+	// can be used in targeted tests.
+	RegabiReflect bool
+	// RegabiDefer enables desugaring defer and go calls
+	// into argument-less closures.
+	RegabiDefer bool
+	// RegabiArgs enables register arguments/results in all
+	// compiled Go functions.
+	//
+	// Requires wrappers, reflect, defer.
+	RegabiArgs bool
+}
+
 // Toolchain experiments.
 // These are controlled by the GOEXPERIMENT environment
 // variable recorded when the toolchain is built.
@@ -199,7 +253,12 @@ var exper = []struct {
 	{"fieldtrack", &Fieldtrack_enabled},
 	{"preemptibleloops", &Preemptibleloops_enabled},
 	{"staticlockranking", &Staticlockranking_enabled},
-	{"regabi", &Regabi_enabled},
+	{"regabi", &Experiment.regabi},
+	{"regabiwrappers", &Experiment.RegabiWrappers},
+	{"regabig", &Experiment.RegabiG},
+	{"regabireflect", &Experiment.RegabiReflect},
+	{"regabidefer", &Experiment.RegabiDefer},
+	{"regabiargs", &Experiment.RegabiArgs},
 }
 
 var defaultExpstring string