cmd/compile: late call expansion for rtcall

Change-Id: I0708c9d649d8a579857330b68d9fbcbbeced29e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/248189
Trust: David Chase <[email protected]>
Run-TryBot: David Chase <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Cherry Zhang <[email protected]>

Author: dr2chase

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

@@ -4353,7 +4353,6 @@ func (s *state) openDeferExit() {
 		} else {
 			s.vars[&memVar] = call
 		}
-
 		// Make sure that the stack slots with pointers are kept live
 		// through the call (which is a pre-emption point). Also, we will
 		// use the first call of the last defer exit to compute liveness
@@ -5076,15 +5075,22 @@ func (s *state) rtcall(fn *obj.LSym, returns bool, results []*types.Type, args .
 	s.prevCall = nil
 	// Write args to the stack
 	off := Ctxt.FixedFrameSize()
+	testLateExpansion := ssa.LateCallExpansionEnabledWithin(s.f)
 	var ACArgs []ssa.Param
 	var ACResults []ssa.Param
+	var callArgs []*ssa.Value
+
 	for _, arg := range args {
 		t := arg.Type
 		off = Rnd(off, t.Alignment())
-		ptr := s.constOffPtrSP(t.PtrTo(), off)
 		size := t.Size()
 		ACArgs = append(ACArgs, ssa.Param{Type: t, Offset: int32(off)})
-		s.store(t, ptr, arg)
+		if testLateExpansion {
+			callArgs = append(callArgs, arg)
+		} else {
+			ptr := s.constOffPtrSP(t.PtrTo(), off)
+			s.store(t, ptr, arg)
+		}
 		off += size
 	}
 	off = Rnd(off, int64(Widthreg))
@@ -5098,8 +5104,17 @@ func (s *state) rtcall(fn *obj.LSym, returns bool, results []*types.Type, args .
 	}
 
 	// Issue call
-	call := s.newValue1A(ssa.OpStaticCall, types.TypeMem, ssa.StaticAuxCall(fn, ACArgs, ACResults), s.mem())
-	s.vars[&memVar] = call
+	var call *ssa.Value
+	aux := ssa.StaticAuxCall(fn, ACArgs, ACResults)
+	if testLateExpansion {
+		callArgs = append(callArgs, s.mem())
+		call = s.newValue0A(ssa.OpStaticLECall, aux.LateExpansionResultType(), aux)
+		call.AddArgs(callArgs...)
+		s.vars[&memVar] = s.newValue1I(ssa.OpSelectN, types.TypeMem, int64(len(ACResults)), call)
+	} else {
+		call = s.newValue1A(ssa.OpStaticCall, types.TypeMem, aux, s.mem())
+		s.vars[&memVar] = call
+	}
 
 	if !returns {
 		// Finish block
@@ -5115,11 +5130,24 @@ func (s *state) rtcall(fn *obj.LSym, returns bool, results []*types.Type, args .
 
 	// Load results
 	res := make([]*ssa.Value, len(results))
-	for i, t := range results {
-		off = Rnd(off, t.Alignment())
-		ptr := s.constOffPtrSP(types.NewPtr(t), off)
-		res[i] = s.load(t, ptr)
-		off += t.Size()
+	if testLateExpansion {
+		for i, t := range results {
+			off = Rnd(off, t.Alignment())
+			if canSSAType(t) {
+				res[i] = s.newValue1I(ssa.OpSelectN, t, int64(i), call)
+			} else {
+				addr := s.newValue1I(ssa.OpSelectNAddr, types.NewPtr(t), int64(i), call)
+				res[i] = s.rawLoad(t, addr)
+			}
+			off += t.Size()
+		}
+	} else {
+		for i, t := range results {
+			off = Rnd(off, t.Alignment())
+			ptr := s.constOffPtrSP(types.NewPtr(t), off)
+			res[i] = s.load(t, ptr)
+			off += t.Size()
+		}
 	}
 	off = Rnd(off, int64(Widthptr))