ir: add explicit AddrSpace field for optional address space of InstAlloca

Prior to this commit, the AddrSpace was stored in the cached
result pointer type of InstAlloca (i.e. in the Typ field).
However, this approach was fragile as resetting the type cache would
remove the information about address space.

Author: mewmew

asm/inst_memory.go

@@ -117,7 +117,7 @@ func (fgen *funcGen) irAllocaInst(new ir.Instruction, old *ast.AllocaInst) error
 	}
 	// (optional) Address space; stored in i.Typ.
 	if n, ok := old.AddrSpace(); ok {
-		inst.Typ.AddrSpace = irAddrSpace(n)
+		inst.AddrSpace = irAddrSpace(n)
 	}
 	// (optional) Metadata.
 	md, err := fgen.gen.irMetadataAttachments(old.Metadata())

ir/inst_memory.go

@@ -35,6 +35,8 @@ type InstAlloca struct {
 	SwiftError bool
 	// (optional) Alignment; zero if not present.
 	Align Align
+	// (optional) Address space; zero if not present.
+	AddrSpace types.AddrSpace
 	// (optional) Metadata.
 	Metadata
 }
@@ -58,6 +60,7 @@ func (inst *InstAlloca) Type() types.Type {
 	// Cache type if not present.
 	if inst.Typ == nil {
 		inst.Typ = types.NewPointer(inst.ElemType)
+		inst.Typ.AddrSpace = inst.AddrSpace
 	}
 	return inst.Typ
 }
@@ -82,8 +85,8 @@ func (inst *InstAlloca) LLString() string {
 	if inst.Align != 0 {
 		fmt.Fprintf(buf, ", %s", inst.Align)
 	}
-	if inst.Typ.AddrSpace != 0 {
-		fmt.Fprintf(buf, ", %s", inst.Typ.AddrSpace)
+	if inst.AddrSpace != 0 {
+		fmt.Fprintf(buf, ", %s", inst.AddrSpace)
 	}
 	for _, md := range inst.Metadata {
 		fmt.Fprintf(buf, ", %s", md)