compiler: rename getZeroValue to llvm.ConstNull

It does the same thing but should be more complete, and it probably is
faster as well (just one CGo call instead of several).

Author: aykevl

compiler/calls.go

@@ -163,7 +163,7 @@ func (c *Compiler) collapseFormalParamInternal(t llvm.Type, fields []llvm.Value)
 	switch t.TypeKind() {
 	case llvm.StructTypeKind:
 		if len(c.flattenAggregateType(t)) <= MaxFieldsPerParam {
-			value := c.getZeroValue(t)
+			value := llvm.ConstNull(t)
 			for i, subtyp := range t.StructElementTypes() {
 				structField, remaining := c.collapseFormalParamInternal(subtyp, fields)
 				fields = remaining

compiler/channel.go

@@ -124,7 +124,7 @@ func (c *Compiler) emitSelect(frame *Frame, expr *ssa.Select) llvm.Value {
 	chanSelectStateType := c.getLLVMRuntimeType("chanSelectState")
 	for _, state := range expr.States {
 		ch := c.getValue(frame, state.Chan)
-		selectState := c.getZeroValue(chanSelectStateType)
+		selectState := llvm.ConstNull(chanSelectStateType)
 		selectState = c.builder.CreateInsertValue(selectState, ch, 0, "")
 		switch state.Dir {
 		case types.RecvOnly:

compiler/compiler.go

@@ -563,42 +563,6 @@ func (c *Compiler) getLLVMType(goType types.Type) llvm.Type {
 	}
 }
 
-// Return a zero LLVM value for any LLVM type. Setting this value as an
-// initializer has the same effect as setting 'zeroinitializer' on a value.
-// Sadly, I haven't found a way to do it directly with the Go API but this works
-// just fine.
-func (c *Compiler) getZeroValue(typ llvm.Type) llvm.Value {
-	switch typ.TypeKind() {
-	case llvm.ArrayTypeKind:
-		subTyp := typ.ElementType()
-		subVal := c.getZeroValue(subTyp)
-		vals := make([]llvm.Value, typ.ArrayLength())
-		for i := range vals {
-			vals[i] = subVal
-		}
-		return llvm.ConstArray(subTyp, vals)
-	case llvm.FloatTypeKind, llvm.DoubleTypeKind:
-		return llvm.ConstFloat(typ, 0.0)
-	case llvm.IntegerTypeKind:
-		return llvm.ConstInt(typ, 0, false)
-	case llvm.PointerTypeKind:
-		return llvm.ConstPointerNull(typ)
-	case llvm.StructTypeKind:
-		types := typ.StructElementTypes()
-		vals := make([]llvm.Value, len(types))
-		for i, subTyp := range types {
-			vals[i] = c.getZeroValue(subTyp)
-		}
-		if typ.StructName() != "" {
-			return llvm.ConstNamedStruct(typ, vals)
-		} else {
-			return c.ctx.ConstStruct(vals, false)
-		}
-	default:
-		panic("unknown LLVM zero inititializer: " + typ.String())
-	}
-}
-
 // Is this a pointer type of some sort? Can be unsafe.Pointer or any *T pointer.
 func isPointer(typ types.Type) bool {
 	if _, ok := typ.(*types.Pointer); ok {
@@ -1132,7 +1096,7 @@ func (c *Compiler) parseInstr(frame *Frame, instr ssa.Instruction) {
 			c.builder.CreateRet(c.getValue(frame, instr.Results[0]))
 		} else {
 			// Multiple return values. Put them all in a struct.
-			retVal := c.getZeroValue(frame.fn.LLVMFn.Type().ElementType().ReturnType())
+			retVal := llvm.ConstNull(frame.fn.LLVMFn.Type().ElementType().ReturnType())
 			for i, result := range instr.Results {
 				val := c.getValue(frame, result)
 				retVal = c.builder.CreateInsertValue(retVal, val, i, "")
@@ -1460,7 +1424,7 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 		} else {
 			buf := c.createEntryBlockAlloca(typ, expr.Comment)
 			if c.targetData.TypeAllocSize(typ) != 0 {
-				c.builder.CreateStore(c.getZeroValue(typ), buf) // zero-initialize var
+				c.builder.CreateStore(llvm.ConstNull(typ), buf) // zero-initialize var
 			}
 			return buf, nil
 		}
@@ -1767,7 +1731,7 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 			panic("unknown type in range: " + typ.String())
 		}
 		it, _, _ := c.createTemporaryAlloca(iteratorType, "range.it")
-		c.builder.CreateStore(c.getZeroValue(iteratorType), it)
+		c.builder.CreateStore(llvm.ConstNull(iteratorType), it)
 		return it, nil
 	case *ssa.Select:
 		return c.emitSelect(frame, expr), nil
@@ -2349,12 +2313,12 @@ func (c *Compiler) parseConst(prefix string, expr *ssa.Const) llvm.Value {
 		if expr.Value != nil {
 			panic("expected nil chan constant")
 		}
-		return c.getZeroValue(c.getLLVMType(expr.Type()))
+		return llvm.ConstNull(c.getLLVMType(expr.Type()))
 	case *types.Signature:
 		if expr.Value != nil {
 			panic("expected nil signature constant")
 		}
-		return c.getZeroValue(c.getLLVMType(expr.Type()))
+		return llvm.ConstNull(c.getLLVMType(expr.Type()))
 	case *types.Interface:
 		if expr.Value != nil {
 			panic("expected nil interface constant")
@@ -2389,7 +2353,7 @@ func (c *Compiler) parseConst(prefix string, expr *ssa.Const) llvm.Value {
 			panic("non-nil map constant")
 		}
 		llvmType := c.getLLVMType(typ)
-		return c.getZeroValue(llvmType)
+		return llvm.ConstNull(llvmType)
 	default:
 		panic("unknown constant: " + expr.String())
 	}
@@ -2581,7 +2545,7 @@ func (c *Compiler) parseUnOp(frame *Frame, unop *ssa.UnOp) (llvm.Value, error) {
 		unop.X.Type().Underlying().(*types.Pointer).Elem()
 		if c.targetData.TypeAllocSize(x.Type().ElementType()) == 0 {
 			// zero-length data
-			return c.getZeroValue(x.Type().ElementType()), nil
+			return llvm.ConstNull(x.Type().ElementType()), nil
 		} else if strings.HasSuffix(unop.X.String(), "$funcaddr") {
 			// CGo function pointer. The cgo part has rewritten CGo function
 			// pointers as stub global variables of the form:

compiler/defer.go

@@ -122,7 +122,7 @@ func (c *Compiler) emitDefer(frame *Frame, instr *ssa.Defer) {
 
 	// Make a struct out of the collected values to put in the defer frame.
 	deferFrameType := c.ctx.StructType(valueTypes, false)
-	deferFrame := c.getZeroValue(deferFrameType)
+	deferFrame := llvm.ConstNull(deferFrameType)
 	for i, value := range values {
 		deferFrame = c.builder.CreateInsertValue(deferFrame, value, i, "")
 	}

compiler/gc.go

@@ -134,7 +134,7 @@ func (c *Compiler) makeGCStackSlots() bool {
 		}
 		stackChainStart := c.mod.NamedGlobal("runtime.stackChainStart")
 		if !stackChainStart.IsNil() {
-			stackChainStart.SetInitializer(c.getZeroValue(stackChainStart.Type().ElementType()))
+			stackChainStart.SetInitializer(llvm.ConstNull(stackChainStart.Type().ElementType()))
 			stackChainStart.SetGlobalConstant(true)
 		}
 	}
@@ -198,7 +198,7 @@ func (c *Compiler) makeGCStackSlots() bool {
 		panic("stack chain start not found!")
 	}
 	stackChainStartType := stackChainStart.Type().ElementType()
-	stackChainStart.SetInitializer(c.getZeroValue(stackChainStartType))
+	stackChainStart.SetInitializer(llvm.ConstNull(stackChainStartType))
 
 	// Iterate until runtime.trackPointer has no uses left.
 	for use := trackPointer.FirstUse(); !use.IsNil(); use = trackPointer.FirstUse() {
@@ -303,7 +303,7 @@ func (c *Compiler) makeGCStackSlots() bool {
 		// Create the stack object at the function entry.
 		c.builder.SetInsertPointBefore(fn.EntryBasicBlock().FirstInstruction())
 		stackObject := c.builder.CreateAlloca(stackObjectType, "gc.stackobject")
-		initialStackObject := c.getZeroValue(stackObjectType)
+		initialStackObject := llvm.ConstNull(stackObjectType)
 		numSlots := (c.targetData.TypeAllocSize(stackObjectType) - c.targetData.TypeAllocSize(c.i8ptrType)*2) / uint64(c.targetData.ABITypeAlignment(c.uintptrType))
 		numSlotsValue := llvm.ConstInt(c.uintptrType, numSlots, false)
 		initialStackObject = llvm.ConstInsertValue(initialStackObject, numSlotsValue, []uint32{1})

compiler/interface.go

@@ -74,7 +74,7 @@ func (c *Compiler) getTypeCode(typ types.Type) llvm.Value {
 		}
 		if !references.IsNil() {
 			// Set the 'references' field of the runtime.typecodeID struct.
-			globalValue := c.getZeroValue(global.Type().ElementType())
+			globalValue := llvm.ConstNull(global.Type().ElementType())
 			globalValue = llvm.ConstInsertValue(globalValue, references, []uint32{0})
 			if length != 0 {
 				lengthValue := llvm.ConstInt(c.uintptrType, uint64(length), false)
@@ -96,9 +96,9 @@ func (c *Compiler) makeStructTypeFields(typ *types.Struct) llvm.Value {
 	runtimeStructField := c.getLLVMRuntimeType("structField")
 	structGlobalType := llvm.ArrayType(runtimeStructField, typ.NumFields())
 	structGlobal := llvm.AddGlobal(c.mod, structGlobalType, "reflect/types.structFields")
-	structGlobalValue := c.getZeroValue(structGlobalType)
+	structGlobalValue := llvm.ConstNull(structGlobalType)
 	for i := 0; i < typ.NumFields(); i++ {
-		fieldGlobalValue := c.getZeroValue(runtimeStructField)
+		fieldGlobalValue := llvm.ConstNull(runtimeStructField)
 		fieldGlobalValue = llvm.ConstInsertValue(fieldGlobalValue, c.getTypeCode(typ.Field(i).Type()), []uint32{0})
 		fieldName := c.makeGlobalArray([]byte(typ.Field(i).Name()), "reflect/types.structFieldName", c.ctx.Int8Type())
 		fieldName.SetLinkage(llvm.PrivateLinkage)
@@ -380,7 +380,7 @@ func (c *Compiler) parseTypeAssert(frame *Frame, expr *ssa.TypeAssert) llvm.Valu
 	// Continue after the if statement.
 	c.builder.SetInsertPointAtEnd(nextBlock)
 	phi := c.builder.CreatePHI(assertedType, "typeassert.value")
-	phi.AddIncoming([]llvm.Value{c.getZeroValue(assertedType), valueOk}, []llvm.BasicBlock{prevBlock, okBlock})
+	phi.AddIncoming([]llvm.Value{llvm.ConstNull(assertedType), valueOk}, []llvm.BasicBlock{prevBlock, okBlock})
 
 	if expr.CommaOk {
 		tuple := c.ctx.ConstStruct([]llvm.Value{llvm.Undef(assertedType), llvm.Undef(c.ctx.Int1Type())}, false) // create empty tuple

compiler/optimizer.go

@@ -289,7 +289,7 @@ func (c *Compiler) OptimizeAllocs() {
 			sizeInWords := (size + uint64(alignment) - 1) / uint64(alignment)
 			allocaType := llvm.ArrayType(c.ctx.IntType(alignment*8), int(sizeInWords))
 			alloca := c.builder.CreateAlloca(allocaType, "stackalloc.alloca")
-			zero := c.getZeroValue(alloca.Type().ElementType())
+			zero := llvm.ConstNull(alloca.Type().ElementType())
 			c.builder.CreateStore(zero, alloca)
 			stackalloc := c.builder.CreateBitCast(alloca, bitcast.Type(), "stackalloc")
 			bitcast.ReplaceAllUsesWith(stackalloc)

compiler/symbol.go

@@ -61,7 +61,7 @@ func (c *Compiler) getGlobal(g *ssa.Global) llvm.Value {
 		llvmType := c.getLLVMType(g.Type().(*types.Pointer).Elem())
 		llvmGlobal = llvm.AddGlobal(c.mod, llvmType, info.linkName)
 		if !info.extern {
-			llvmGlobal.SetInitializer(c.getZeroValue(llvmType))
+			llvmGlobal.SetInitializer(llvm.ConstNull(llvmType))
 			llvmGlobal.SetLinkage(llvm.InternalLinkage)
 		}
 	}

compiler/wordpack.go

@@ -101,7 +101,7 @@ func (c *Compiler) emitPointerUnpack(ptr llvm.Value, valueTypes []llvm.Type) []l
 	for i, valueType := range valueTypes {
 		if c.targetData.TypeAllocSize(valueType) == 0 {
 			// This value has length zero, so there's nothing to load.
-			values[i] = c.getZeroValue(valueType)
+			values[i] = llvm.ConstNull(valueType)
 			continue
 		}
 		indices := []llvm.Value{

interp/frame.go

@@ -86,7 +86,7 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 		case !inst.IsAAllocaInst().IsNil():
 			allocType := inst.Type().ElementType()
 			alloca := llvm.AddGlobal(fr.Mod, allocType, fr.pkgName+"$alloca")
-			alloca.SetInitializer(getZeroValue(allocType))
+			alloca.SetInitializer(llvm.ConstNull(allocType))
 			alloca.SetLinkage(llvm.InternalLinkage)
 			fr.locals[inst] = &LocalValue{
 				Underlying: alloca,
@@ -253,7 +253,7 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 					allocType = llvm.ArrayType(allocType, elementCount)
 				}
 				alloc := llvm.AddGlobal(fr.Mod, allocType, fr.pkgName+"$alloc")
-				alloc.SetInitializer(getZeroValue(allocType))
+				alloc.SetInitializer(llvm.ConstNull(allocType))
 				alloc.SetLinkage(llvm.InternalLinkage)
 				result := &LocalValue{
 					Underlying: alloc,
@@ -312,7 +312,7 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 				stringType := fr.Mod.GetTypeByName("runtime._string")
 				retPtr := llvm.ConstGEP(global, getLLVMIndices(fr.Mod.Context().Int32Type(), []uint32{0, 0}))
 				retLen := llvm.ConstInt(stringType.StructElementTypes()[1], uint64(len(result)), false)
-				ret := getZeroValue(stringType)
+				ret := llvm.ConstNull(stringType)
 				ret = llvm.ConstInsertValue(ret, retPtr, []uint32{0})
 				ret = llvm.ConstInsertValue(ret, retLen, []uint32{1})
 				fr.locals[inst] = &LocalValue{fr.Eval, ret}
@@ -335,7 +335,7 @@ func (fr *frame) evalBasicBlock(bb, incoming llvm.BasicBlock, indent string) (re
 				sliceType := inst.Type()
 				retPtr := llvm.ConstGEP(global, getLLVMIndices(fr.Mod.Context().Int32Type(), []uint32{0, 0}))
 				retLen := llvm.ConstInt(sliceType.StructElementTypes()[1], uint64(len(result)), false)
-				ret := getZeroValue(sliceType)
+				ret := llvm.ConstNull(sliceType)
 				ret = llvm.ConstInsertValue(ret, retPtr, []uint32{0}) // ptr
 				ret = llvm.ConstInsertValue(ret, retLen, []uint32{1}) // len
 				ret = llvm.ConstInsertValue(ret, retLen, []uint32{2}) // cap