cmd/compile: add code to expand calls just before late opt

Still needs to generate the calls that will need lowering.

Change-Id: Ifd4e510193441a5e27c462c1f1d704f07bf6dec3
Reviewed-on: https://go-review.googlesource.com/c/go/+/242359
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

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

@@ -433,6 +433,7 @@ var passes = [...]pass{
 	{name: "early fuse", fn: fuseEarly},
 	{name: "decompose builtin", fn: decomposeBuiltIn, required: true},
 	{name: "softfloat", fn: softfloat, required: true},
+	{name: "expand calls", fn:expandCalls, required: true},
 	{name: "late opt", fn: opt, required: true}, // TODO: split required rules and optimizing rules
 	{name: "dead auto elim", fn: elimDeadAutosGeneric},
 	{name: "generic deadcode", fn: deadcode, required: true}, // remove dead stores, which otherwise mess up store chain

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

@@ -0,0 +1,101 @@
+// 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)
+			}
+		}
+	}
+}
+

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

@@ -775,3 +775,25 @@ func (f *Func) logDebugHashMatch(evname, name string) {
 func DebugNameMatch(evname, name string) bool {
 	return os.Getenv(evname) == name
 }
+
+func (f *Func) spSb() (sp, sb *Value) {
+	initpos := f.Entry.Pos
+	for _, v := range f.Entry.Values {
+		if v.Op == OpSB {
+			sb = v
+		}
+		if v.Op == OpSP {
+			sp = v
+		}
+		if sb != nil && sp != nil {
+			break
+		}
+	}
+	if sb == nil {
+		sb = f.Entry.NewValue0(initpos, OpSB, f.Config.Types.Uintptr)
+	}
+	if sp == nil {
+		sp = f.Entry.NewValue0(initpos, OpSP, f.Config.Types.Uintptr)
+	}
+	return
+}

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

@@ -79,6 +79,41 @@ type AuxCall struct {
 	results []Param
 }
 
+// OffsetOfResult returns the SP offset of result which (indexed 0, 1, etc).
+func (a *AuxCall) OffsetOfResult(which int64) int64 {
+	return int64(a.results[which].Offset)
+}
+// OffsetOfArg returns the SP offset of argument which (indexed 0, 1, etc).
+func (a *AuxCall) OffsetOfArg(which int64) int64 {
+	return int64(a.args[which].Offset)
+}
+// TypeOfResult returns the type of result which (indexed 0, 1, etc).
+func (a *AuxCall) TypeOfResult(which int64) *types.Type {
+	return a.results[which].Type
+}
+// TypeOfArg returns the type of argument which (indexed 0, 1, etc).
+func (a *AuxCall) TypeOfArg(which int64) *types.Type {
+	return a.args[which].Type
+}
+// SizeOfResult returns the size of result which (indexed 0, 1, etc).
+func (a *AuxCall) SizeOfResult(which int64) int64 {
+	return a.TypeOfResult(which).Width
+}
+// SizeOfArg returns the size of argument which (indexed 0, 1, etc).
+func (a *AuxCall) SizeOfArg(which int64) int64 {
+	return a.TypeOfArg(which).Width
+}
+
+// NResults returns the number of results
+func (a *AuxCall) NResults() int64 {
+	return int64(len(a.results))
+}
+
+// NArgs returns the number of arguments
+func (a *AuxCall) NArgs() int64 {
+	return int64(len(a.args))
+}
+
 // String returns
 // "AuxCall{<fn>(<args>)}"             if len(results) == 0;
 // "AuxCall{<fn>(<args>)<results[0]>}" if len(results) == 1;

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

@@ -125,23 +125,7 @@ func writebarrier(f *Func) {
 			// lazily initialize global values for write barrier test and calls
 			// find SB and SP values in entry block
 			initpos := f.Entry.Pos
-			for _, v := range f.Entry.Values {
-				if v.Op == OpSB {
-					sb = v
-				}
-				if v.Op == OpSP {
-					sp = v
-				}
-				if sb != nil && sp != nil {
-					break
-				}
-			}
-			if sb == nil {
-				sb = f.Entry.NewValue0(initpos, OpSB, f.Config.Types.Uintptr)
-			}
-			if sp == nil {
-				sp = f.Entry.NewValue0(initpos, OpSP, f.Config.Types.Uintptr)
-			}
+			sp, sb = f.spSb()
 			wbsym := f.fe.Syslook("writeBarrier")
 			wbaddr = f.Entry.NewValue1A(initpos, OpAddr, f.Config.Types.UInt32Ptr, wbsym, sb)
 			gcWriteBarrier = f.fe.Syslook("gcWriteBarrier")