compiler: centralize loads and stores of SSA values

Map, channel, index, and goroutine lowering each create allocas, store
SSA values into them, load results, and emit lifetime intrinsics.

Add helpers for these operations and use runtimeValueResult for runtime
calls that write a value and an optional comma-ok result. The generated
LLVM IR is unchanged.

compiler/compiler.go

@@ -1546,10 +1546,8 @@ func (b *builder) createInstruction(instr ssa.Instruction) {
 		b.CreateBr(blockJump)
 	case *ssa.MapUpdate:
 		m := b.getValue(instr.Map, getPos(instr))
-		key := b.getValue(instr.Key, getPos(instr))
-		value := b.getValue(instr.Value, getPos(instr))
 		mapType := instr.Map.Type().Underlying().(*types.Map)
-		b.createMapUpdate(mapType.Key(), m, key, value, instr.Pos())
+		b.createMapUpdate(mapType.Key(), m, instr.Key, instr.Value, instr.Pos())
 	case *ssa.Panic:
 		value := b.getValue(instr.X, getPos(instr))
 		b.createRuntimeInvoke("_panic", []llvm.Value{value}, "")
@@ -1584,18 +1582,80 @@ func (b *builder) createInstruction(instr ssa.Instruction) {
 		b.createChanSend(instr)
 	case *ssa.Store:
 		llvmAddr := b.getValue(instr.Addr, getPos(instr))
-		llvmVal := b.getValue(instr.Val, getPos(instr))
 		b.createNilCheck(instr.Addr, llvmAddr, "store")
-		if b.targetData.TypeAllocSize(llvmVal.Type()) == 0 {
+		llvmType := b.getLLVMType(instr.Val.Type())
+		if b.targetData.TypeAllocSize(llvmType) == 0 {
 			// nothing to store
 			return
 		}
-		b.CreateStore(llvmVal, llvmAddr)
+		b.storeValue(llvmAddr, instr.Val)
 	default:
 		b.addError(instr.Pos(), "unknown instruction: "+instr.String())
 	}
 }
 
+func (b *builder) storeValue(dst llvm.Value, value ssa.Value) {
+	b.CreateStore(b.getValue(value, getPos(value)), dst)
+}
+
+func (b *builder) loadFromStorage(ptr llvm.Value, typ types.Type, name string) llvm.Value {
+	return b.CreateLoad(b.getLLVMType(typ), ptr, name)
+}
+
+func (b *builder) getValueStorage(value ssa.Value, name string) (ptr, size llvm.Value) {
+	typ := b.getLLVMType(value.Type())
+	ptr, size = b.createTemporaryAlloca(typ, name)
+	b.storeValue(ptr, value)
+	return ptr, size
+}
+
+type runtimeValueResult struct {
+	valueType  llvm.Type
+	resultType llvm.Type
+	valuePtr   llvm.Value
+	valueSize  llvm.Value
+	temporary  bool
+	zero       bool
+	commaOk    bool
+}
+
+func (b *builder) createRuntimeValueResult(valueType llvm.Type, commaOk, zeroAsNull bool, name string) runtimeValueResult {
+	result := runtimeValueResult{
+		valueType:  valueType,
+		resultType: valueType,
+		commaOk:    commaOk,
+	}
+	if commaOk {
+		result.resultType = b.ctx.StructType([]llvm.Type{valueType, b.ctx.Int1Type()}, false)
+	}
+	if zeroAsNull && b.targetData.TypeAllocSize(valueType) == 0 {
+		result.valuePtr = llvm.ConstNull(b.dataPtrType)
+		result.zero = true
+		return result
+	}
+	result.valuePtr, result.valueSize = b.createTemporaryAlloca(valueType, name+".value")
+	result.temporary = true
+	return result
+}
+
+func (r runtimeValueResult) finish(b *builder, commaOk llvm.Value, name string) llvm.Value {
+	var value llvm.Value
+	if r.zero {
+		value = llvm.ConstNull(r.valueType)
+	} else {
+		value = b.CreateLoad(r.valueType, r.valuePtr, name)
+	}
+	if r.temporary {
+		b.emitLifetimeEnd(r.valuePtr, r.valueSize)
+	}
+	if !r.commaOk {
+		return value
+	}
+	result := llvm.Undef(r.resultType)
+	result = b.CreateInsertValue(result, value, 0, "")
+	return b.CreateInsertValue(result, commaOk, 1, "")
+}
+
 // createBuiltin lowers a builtin Go function (append, close, delete, etc.) to
 // LLVM IR. It uses runtime calls for some builtins.
 func (b *builder) createBuiltin(argTypes []types.Type, argValues []llvm.Value, callName string, pos token.Pos) (llvm.Value, error) {
@@ -2270,11 +2330,11 @@ func (b *builder) createExpr(expr ssa.Value) (llvm.Value, error) {
 	case *ssa.Global:
 		panic("global is not an expression")
 	case *ssa.Index:
-		collection := b.getValue(expr.X, getPos(expr))
 		index := b.getValue(expr.Index, getPos(expr))
 
 		switch xType := expr.X.Type().Underlying().(type) {
 		case *types.Basic: // extract byte from string
+			collection := b.getValue(expr.X, getPos(expr))
 			// Value type must be a string, which is a basic type.
 			if xType.Info()&types.IsString == 0 {
 				panic("lookup on non-string?")
@@ -2308,12 +2368,11 @@ func (b *builder) createExpr(expr ssa.Value) (llvm.Value, error) {
 
 			// Can't load directly from array (as index is non-constant), so
 			// have to do it using an alloca+gep+load.
-			arrayType := collection.Type()
-			alloca, allocaSize := b.createTemporaryAlloca(arrayType, "index.alloca")
-			b.CreateStore(collection, alloca)
+			arrayType := b.getLLVMType(expr.X.Type())
+			alloca, allocaSize := b.getValueStorage(expr.X, "index.alloca")
 			zero := llvm.ConstInt(b.ctx.Int32Type(), 0, false)
 			ptr := b.CreateInBoundsGEP(arrayType, alloca, []llvm.Value{zero, index}, "index.gep")
-			result := b.CreateLoad(arrayType.ElementType(), ptr, "index.load")
+			result := b.loadFromStorage(ptr, expr.Type(), "index.load")
 			b.emitLifetimeEnd(alloca, allocaSize)
 			return result, nil
 		default:
@@ -2373,12 +2432,11 @@ func (b *builder) createExpr(expr ssa.Value) (llvm.Value, error) {
 		}
 	case *ssa.Lookup: // map lookup
 		value := b.getValue(expr.X, getPos(expr))
-		index := b.getValue(expr.Index, getPos(expr))
 		valueType := expr.Type()
 		if expr.CommaOk {
 			valueType = valueType.(*types.Tuple).At(0).Type()
 		}
-		return b.createMapLookup(expr.X.Type().Underlying().(*types.Map).Key(), valueType, value, index, expr.CommaOk, expr.Pos())
+		return b.createMapLookup(expr.X.Type().Underlying().(*types.Map).Key(), valueType, value, expr.Index, expr.CommaOk, expr.Pos())
 	case *ssa.MakeChan:
 		return b.createMakeChan(expr), nil
 	case *ssa.MakeClosure:
@@ -3453,8 +3511,7 @@ func (b *builder) createUnOp(unop *ssa.UnOp) (llvm.Value, error) {
 			return fn, nil
 		} else {
 			b.createNilCheck(unop.X, x, "deref")
-			load := b.CreateLoad(valueType, x, "")
-			return load, nil
+			return b.loadFromStorage(x, unop.Type(), ""), nil
 		}
 	case token.XOR: // ^x, toggle all bits in integer
 		return b.CreateXor(x, llvm.ConstInt(x.Type(), ^uint64(0), false), ""), nil