[dev.typeparams] cmd/compile, runtime: simplify opendefer metadata

Now that deferred functions are always argumentless, we don't
need the metadata for the frame size, number of arguments, and
the information about each argument.

Change-Id: I99e75248a22bda6efbdf2012a2f35beca4c18fd7
Reviewed-on: https://go-review.googlesource.com/c/go/+/326061
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

src/cmd/compile/internal/ssagen/ssa.go

@@ -324,43 +324,21 @@ func dvarint(x *obj.LSym, off int, v int64) int {
 // for stack variables are specified as the number of bytes below varp (pointer to the
 // top of the local variables) for their starting address. The format is:
 //
-//  - Max total argument size among all the defers
 //  - Offset of the deferBits variable
 //  - Number of defers in the function
 //  - Information about each defer call, in reverse order of appearance in the function:
-//    - Total argument size of the call
 //    - Offset of the closure value to call
-//    - Number of arguments (including interface receiver or method receiver as first arg)
-//    - Information about each argument
-//      - Offset of the stored defer argument in this function's frame
-//      - Size of the argument
-//      - Offset of where argument should be placed in the args frame when making call
 func (s *state) emitOpenDeferInfo() {
 	x := base.Ctxt.Lookup(s.curfn.LSym.Name + ".opendefer")
 	s.curfn.LSym.Func().OpenCodedDeferInfo = x
 	off := 0
-
-	// Compute maxargsize (max size of arguments for all defers)
-	// first, so we can output it first to the funcdata
-	var maxargsize int64
-	for i := len(s.openDefers) - 1; i >= 0; i-- {
-		r := s.openDefers[i]
-		argsize := r.n.X.Type().ArgWidth() // TODO register args: but maybe use of abi0 will make this easy
-		if argsize > maxargsize {
-			maxargsize = argsize
-		}
-	}
-	off = dvarint(x, off, maxargsize)
 	off = dvarint(x, off, -s.deferBitsTemp.FrameOffset())
 	off = dvarint(x, off, int64(len(s.openDefers)))
 
 	// Write in reverse-order, for ease of running in that order at runtime
 	for i := len(s.openDefers) - 1; i >= 0; i-- {
 		r := s.openDefers[i]
-		off = dvarint(x, off, r.n.X.Type().ArgWidth())
 		off = dvarint(x, off, -r.closureNode.FrameOffset())
-		numArgs := 0
-		off = dvarint(x, off, int64(numArgs))
 	}
 }
 

src/runtime/panic.go

@@ -720,8 +720,7 @@ func addOneOpenDeferFrame(gp *g, pc uintptr, sp unsafe.Pointer) {
 					throw("missing deferreturn")
 				}
 
-				maxargsize, _ := readvarintUnsafe(fd)
-				d1 := newdefer(int32(maxargsize))
+				d1 := newdefer(0)
 				d1.openDefer = true
 				d1._panic = nil
 				// These are the pc/sp to set after we've
@@ -782,27 +781,15 @@ func runOpenDeferFrame(gp *g, d *_defer) bool {
 	done := true
 	fd := d.fd
 
-	// Skip the maxargsize
-	_, fd = readvarintUnsafe(fd)
 	deferBitsOffset, fd := readvarintUnsafe(fd)
 	nDefers, fd := readvarintUnsafe(fd)
 	deferBits := *(*uint8)(unsafe.Pointer(d.varp - uintptr(deferBitsOffset)))
 
 	for i := int(nDefers) - 1; i >= 0; i-- {
 		// read the funcdata info for this defer
-		var argWidth, closureOffset, nArgs uint32
-		argWidth, fd = readvarintUnsafe(fd)
+		var closureOffset uint32
 		closureOffset, fd = readvarintUnsafe(fd)
-		nArgs, fd = readvarintUnsafe(fd)
-		if argWidth != 0 || nArgs != 0 {
-			throw("defer with non-empty frame")
-		}
 		if deferBits&(1<<i) == 0 {
-			for j := uint32(0); j < nArgs; j++ {
-				_, fd = readvarintUnsafe(fd)
-				_, fd = readvarintUnsafe(fd)
-				_, fd = readvarintUnsafe(fd)
-			}
 			continue
 		}
 		closure := *(*func())(unsafe.Pointer(d.varp - uintptr(closureOffset)))