1 files changed, 100 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/ssa/expand_calls.go b/src/cmd/compile/internal/ssa/expand_calls.go
new file mode 100644
index 0000000000..34cff51c00
--- /dev/null
+++ b/src/cmd/compile/internal/ssa/expand_calls.go
@@ -0,0 +1,100 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ssa
+
+import "cmd/compile/internal/types"
+
+// expandCalls converts LE (Late Expansion) calls that act like they receive value args into a lower-level form
+// that is more oriented to a platform's ABI.  The SelectN operations that extract results are also rewritten into
+// more appropriate forms.
+func expandCalls(f *Func) {
+	canSSAType := f.fe.CanSSA
+	sp, _ := f.spSb()
+	// Calls that need lowering have some number of inputs, including a memory input,
+	// and produce a tuple of (value1, value2, ..., mem) where valueK may or may not be SSA-able.
+
+	// With the current ABI those inputs need to be converted into stores to memory,
+	// rethreading the call's memory input to the first, and the new call now receiving the last.
+
+	// With the current ABI, the outputs need to be converted to loads, which will all use the call's
+	// memory output as their input.
+
+	// Step 1: find all references to calls as values and rewrite those.
+	for _, b := range f.Blocks {
+		for _, v := range b.Values {
+			switch v.Op {
+			case OpSelectN:
+				call := v.Args[0]
+				aux := call.Aux.(*AuxCall)
+				which := v.AuxInt
+				t := v.Type
+				if which == aux.NResults() { // mem is after the results.
+					// rewrite v as a Copy of call -- the replacement call will produce a mem.
+					v.copyOf(call)
+				} else {
+					pt := types.NewPtr(t)
+					if canSSAType(t) {
+						off := f.ConstOffPtrSP(pt, aux.OffsetOfResult(which), sp)
+						v.reset(OpLoad)
+						v.SetArgs2(off, call)
+					} else {
+						panic("Should not have non-SSA-able OpSelectN")
+					}
+				}
+				v.Type = t // not right for the mem operand yet, but will be when call is rewritten.
+
+			case OpSelectNAddr:
+				call := v.Args[0]
+				which := v.AuxInt
+				aux := call.Aux.(*AuxCall)
+				pt := v.Type
+				off := f.ConstOffPtrSP(pt, aux.OffsetOfResult(which), sp)
+				v.copyOf(off)
+			}
+		}
+	}
+
+	// Step 2: rewrite the calls
+	for _, b := range f.Blocks {
+		for _, v := range b.Values {
+			switch v.Op {
+			case OpStaticLECall:
+				// Thread the stores on the memory arg
+				m0 := v.Args[len(v.Args)-1]
+				mem := m0
+				pos := v.Pos.WithNotStmt()
+				aux := v.Aux.(*AuxCall)
+				auxInt := v.AuxInt
+				for i, a := range v.Args {
+					if a == m0 {
+						break
+					}
+					if a.Op == OpDereference {
+						// "Dereference" of addressed (probably not-SSA-eligible) value becomes Move
+						src := a.Args[0]
+						dst := f.ConstOffPtrSP(src.Type, aux.OffsetOfArg(int64(i)), sp)
+						a.reset(OpMove)
+						a.Pos = pos
+						a.Type = types.TypeMem
+						a.Aux = aux.TypeOfArg(int64(i))
+						a.AuxInt = aux.SizeOfArg(int64(i))
+						a.SetArgs3(dst, src, mem)
+						mem = a
+					} else {
+						// Add a new store.
+						t := aux.TypeOfArg(int64(i))
+						dst := f.ConstOffPtrSP(types.NewPtr(t), aux.OffsetOfArg(int64(i)), sp)
+						mem = b.NewValue3A(pos, OpStore, types.TypeMem, t, dst, a, mem)
+					}
+				}
+				v.reset(OpStaticCall)
+				v.Type = types.TypeMem
+				v.Aux = aux
+				v.AuxInt = auxInt
+				v.SetArgs1(mem)
+			}
+		}
+	}
+}