cmd/compile/internal/gc: factor out beginning of SSAGenState.Call

This commit does not change the semantics of the Call method. Its
purpose is to avoid duplication of code by making PrepareCall available
for separate use by the wasm backend.

Updates #18892

Change-Id: I04a3098f56ebf0d995791c5375dd4c03b6a202a3
Reviewed-on: https://go-review.googlesource.com/103275Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

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

@@ -5080,7 +5080,35 @@ func (s *SSAGenState) AddrScratch(a *obj.Addr) {
 	a.Offset = s.ScratchFpMem.Xoffset
 }
 
+// Call returns a new CALL instruction for the SSA value v.
+// It uses PrepareCall to prepare the call.
 func (s *SSAGenState) Call(v *ssa.Value) *obj.Prog {
+	s.PrepareCall(v)
+
+	p := s.Prog(obj.ACALL)
+	if sym, ok := v.Aux.(*obj.LSym); ok {
+		p.To.Type = obj.TYPE_MEM
+		p.To.Name = obj.NAME_EXTERN
+		p.To.Sym = sym
+	} else {
+		// TODO(mdempsky): Can these differences be eliminated?
+		switch thearch.LinkArch.Family {
+		case sys.AMD64, sys.I386, sys.PPC64, sys.S390X:
+			p.To.Type = obj.TYPE_REG
+		case sys.ARM, sys.ARM64, sys.MIPS, sys.MIPS64:
+			p.To.Type = obj.TYPE_MEM
+		default:
+			Fatalf("unknown indirect call family")
+		}
+		p.To.Reg = v.Args[0].Reg()
+	}
+	return p
+}
+
+// PrepareCall prepares to emit a CALL instruction for v and does call-related bookkeeping.
+// It must be called immediately before emitting the actual CALL instruction,
+// since it emits PCDATA for the stack map at the call (calls are safe points).
+func (s *SSAGenState) PrepareCall(v *ssa.Value) {
 	idx, ok := s.stackMapIndex[v]
 	if !ok {
 		Fatalf("missing stack map index for %v", v.LongString())
@@ -5101,33 +5129,17 @@ func (s *SSAGenState) Call(v *ssa.Value) *obj.Prog {
 		thearch.Ginsnop(s.pp)
 	}
 
-	p = s.Prog(obj.ACALL)
 	if sym, ok := v.Aux.(*obj.LSym); ok {
-		p.To.Type = obj.TYPE_MEM
-		p.To.Name = obj.NAME_EXTERN
-		p.To.Sym = sym
-
 		// Record call graph information for nowritebarrierrec
 		// analysis.
 		if nowritebarrierrecCheck != nil {
 			nowritebarrierrecCheck.recordCall(s.pp.curfn, sym, v.Pos)
 		}
-	} else {
-		// TODO(mdempsky): Can these differences be eliminated?
-		switch thearch.LinkArch.Family {
-		case sys.AMD64, sys.I386, sys.PPC64, sys.S390X:
-			p.To.Type = obj.TYPE_REG
-		case sys.ARM, sys.ARM64, sys.MIPS, sys.MIPS64:
-			p.To.Type = obj.TYPE_MEM
-		default:
-			Fatalf("unknown indirect call family")
-		}
-		p.To.Reg = v.Args[0].Reg()
 	}
+
 	if s.maxarg < v.AuxInt {
 		s.maxarg = v.AuxInt
 	}
-	return p
 }
 
 // fieldIdx finds the index of the field referred to by the ODOT node n.