runtime: remove go115ReduceLiveness and go115RestartSeq

Make them always true. Delete code that are only executed when
they are false.

Change-Id: I6194fa00de23486c2b0a0c9075fe3a09d9c52762
Reviewed-on: https://go-review.googlesource.com/c/go/+/264339
Trust: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Austin Clements <austin@google.com>

src/runtime/debugcall.go

@@ -76,32 +76,14 @@ func debugCallCheck(pc uintptr) string {
 			return
 		}
 
-		if !go115ReduceLiveness {
+		// Check that this isn't an unsafe-point.
-			// Look up PC's register map.
+		if pc != f.entry {
-			pcdata := int32(-1)
+			pc--
-			if pc != f.entry {
+		}
-				pc--
+		up := pcdatavalue(f, _PCDATA_UnsafePoint, pc, nil)
-				pcdata = pcdatavalue(f, _PCDATA_RegMapIndex, pc, nil)
+		if up != _PCDATA_UnsafePointSafe {
-			}
+			// Not at a safe point.
-			if pcdata == -1 {
+			ret = debugCallUnsafePoint
-				pcdata = 0 // in prologue
-			}
-			stkmap := (*stackmap)(funcdata(f, _FUNCDATA_RegPointerMaps))
-			if pcdata == _PCDATA_RegMapUnsafe || stkmap == nil {
-				// Not at a safe point.
-				ret = debugCallUnsafePoint
-				return
-			}
-		} else {
-			// Check that this isn't an unsafe-point.
-			if pc != f.entry {
-				pc--
-			}
-			up := pcdatavalue(f, _PCDATA_UnsafePoint, pc, nil)
-			if up != _PCDATA_UnsafePointSafe {
-				// Not at a safe point.
-				ret = debugCallUnsafePoint
-			}
 		}
 	})
 	return ret

src/runtime/funcdata.h

@@ -8,13 +8,12 @@
 //
 // These must agree with symtab.go and ../cmd/internal/objabi/funcdata.go.
 
-#define PCDATA_RegMapIndex 0
+#define PCDATA_UnsafePoint 0
 #define PCDATA_StackMapIndex 1
 #define PCDATA_InlTreeIndex 2
 
 #define FUNCDATA_ArgsPointerMaps 0 /* garbage collector blocks */
 #define FUNCDATA_LocalsPointerMaps 1
-#define FUNCDATA_RegPointerMaps 2
 #define FUNCDATA_StackObjects 3
 #define FUNCDATA_InlTree 4
 #define FUNCDATA_OpenCodedDeferInfo 5 /* info for func with open-coded defers */

src/runtime/preempt.go

@@ -58,11 +58,6 @@ import (
 	"unsafe"
 )
 
-// Keep in sync with cmd/compile/internal/gc/plive.go:go115ReduceLiveness.
-const go115ReduceLiveness = true
-
-const go115RestartSeq = go115ReduceLiveness && true // enable restartable sequences
-
 type suspendGState struct {
 	g *g
 
@@ -402,24 +397,12 @@ func isAsyncSafePoint(gp *g, pc, sp, lr uintptr) (bool, uintptr) {
 		// use the LR for unwinding, which will be bad.
 		return false, 0
 	}
-	var up int32
+	up, startpc := pcdatavalue2(f, _PCDATA_UnsafePoint, pc)
-	var startpc uintptr
+	if up != _PCDATA_UnsafePointSafe {
-	if !go115ReduceLiveness {
+		// Unsafe-point marked by compiler. This includes
-		smi := pcdatavalue(f, _PCDATA_RegMapIndex, pc, nil)
+		// atomic sequences (e.g., write barrier) and nosplit
-		if smi == _PCDATA_RegMapUnsafe {
+		// functions (except at calls).
-			// Unsafe-point marked by compiler. This includes
+		return false, 0
-			// atomic sequences (e.g., write barrier) and nosplit
-			// functions (except at calls).
-			return false, 0
-		}
-	} else {
-		up, startpc = pcdatavalue2(f, _PCDATA_UnsafePoint, pc)
-		if up != _PCDATA_UnsafePointSafe {
-			// Unsafe-point marked by compiler. This includes
-			// atomic sequences (e.g., write barrier) and nosplit
-			// functions (except at calls).
-			return false, 0
-		}
 	}
 	if fd := funcdata(f, _FUNCDATA_LocalsPointerMaps); fd == nil || fd == unsafe.Pointer(&no_pointers_stackmap) {
 		// This is assembly code. Don't assume it's
@@ -455,25 +438,17 @@ func isAsyncSafePoint(gp *g, pc, sp, lr uintptr) (bool, uintptr) {
 		// in incrementally.
 		return false, 0
 	}
-	if go115RestartSeq {
+	switch up {
-		switch up {
+	case _PCDATA_Restart1, _PCDATA_Restart2:
-		case _PCDATA_Restart1, _PCDATA_Restart2:
+		// Restartable instruction sequence. Back off PC to
-			// Restartable instruction sequence. Back off PC to
+		// the start PC.
-			// the start PC.
+		if startpc == 0 || startpc > pc || pc-startpc > 20 {
-			if startpc == 0 || startpc > pc || pc-startpc > 20 {
+			throw("bad restart PC")
-				throw("bad restart PC")
-			}
-			return true, startpc
-		case _PCDATA_RestartAtEntry:
-			// Restart from the function entry at resumption.
-			return true, f.entry
-		}
-	} else {
-		switch up {
-		case _PCDATA_Restart1, _PCDATA_Restart2, _PCDATA_RestartAtEntry:
-			// go115RestartSeq is not enabled. Treat it as unsafe point.
-			return false, 0
 		}
+		return true, startpc
+	case _PCDATA_RestartAtEntry:
+		// Restart from the function entry at resumption.
+		return true, f.entry
 	}
 	return true, pc
 }

src/runtime/symtab.go

@@ -268,14 +268,12 @@ func (f *Func) funcInfo() funcInfo {
 //
 // See funcdata.h and ../cmd/internal/objabi/funcdata.go.
 const (
-	_PCDATA_RegMapIndex   = 0 // if !go115ReduceLiveness
+	_PCDATA_UnsafePoint   = 0
-	_PCDATA_UnsafePoint   = 0 // if go115ReduceLiveness
 	_PCDATA_StackMapIndex = 1
 	_PCDATA_InlTreeIndex  = 2
 
 	_FUNCDATA_ArgsPointerMaps    = 0
 	_FUNCDATA_LocalsPointerMaps  = 1
-	_FUNCDATA_RegPointerMaps     = 2 // if !go115ReduceLiveness
 	_FUNCDATA_StackObjects       = 3
 	_FUNCDATA_InlTree            = 4
 	_FUNCDATA_OpenCodedDeferInfo = 5
@@ -284,9 +282,6 @@ const (
 )
 
 const (
-	// Only if !go115ReduceLiveness.
-	_PCDATA_RegMapUnsafe = _PCDATA_UnsafePointUnsafe // Unsafe for async preemption
-
 	// PCDATA_UnsafePoint values.
 	_PCDATA_UnsafePointSafe   = -1 // Safe for async preemption
 	_PCDATA_UnsafePointUnsafe = -2 // Unsafe for async preemption