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// 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)
}
}
}
}
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