NIR: Nim intermediate representation (#22777)

Theoretical Benefits / Plans: 

- Typed assembler-like language.
- Allows for a CPS transformation.
- Can replace the existing C backend by a new C backend.
- Can replace the VM.
- Can do more effective "not nil" checking and static array bounds
checking.
- Can be used instead of the DFA.
- Easily translatable to LLVM.
- Reasonably easy to produce native code from.
- Tiny memory consumption. No pointers, no cry.

**In very early stages of development.**

Todo:
- [x] Map Nim types to IR types.
- [ ] Map Nim AST to IR instructions:
  - [x] Map bitsets to bitops.
  - [ ] Implement string cases.
  - [ ] Implement range and index checks.
  - [x] Implement `default(T)` builtin.
  - [x] Implement multi string concat.
- [ ] Write some analysis passes.
- [ ] Write a backend.
- [x] Integrate into the compilation pipeline.

1 files changed, 7 insertions, 9 deletions

diff --git a/compiler/semobjconstr.nim b/compiler/semobjconstr.nim
index 2d366d8fc..ebc8be0c3 100644
--- a/compiler/semobjconstr.nim
+++ b/compiler/semobjconstr.nim
@@ -68,9 +68,7 @@ proc locateFieldInInitExpr(c: PContext, field: PSym, initExpr: PNode): PNode =
     let assignment = initExpr[i]
     if assignment.kind != nkExprColonExpr:
       invalidObjConstr(c, assignment)
-      continue
-
-    if fieldId == considerQuotedIdent(c, assignment[0]).id:
+    elif fieldId == considerQuotedIdent(c, assignment[0]).id:
       return assignment
 
 proc semConstrField(c: PContext, flags: TExprFlags,
@@ -125,7 +123,7 @@ proc pickCaseBranch(caseExpr, matched: PNode): PNode =
       return caseExpr[i]
 
   if endsWithElse:
-    return caseExpr[^1]
+    result = caseExpr[^1]
   else:
     result = nil
 
@@ -138,8 +136,8 @@ iterator directFieldsInRecList(recList: PNode): PNode =
   else:
     doAssert recList.kind == nkRecList
     for field in recList:
-      if field.kind != nkSym: continue
-      yield field
+      if field.kind == nkSym:
+        yield field
 
 template quoteStr(s: string): string = "'" & s & "'"
 
@@ -416,8 +414,8 @@ proc semConstructTypeAux(c: PContext,
     if status in {initPartial, initNone, initUnknown}:
       discard collectMissingFields(c, t.n, constrCtx, result.defaults)
     let base = t[0]
-    if base == nil or base.id == t.id or 
-      base.kind in { tyRef, tyPtr } and base[0].id == t.id: 
+    if base == nil or base.id == t.id or
+      base.kind in {tyRef, tyPtr} and base[0].id == t.id:
         break
     t = skipTypes(base, skipPtrs)
     if t.kind != tyObject:
@@ -463,7 +461,7 @@ proc semObjConstr(c: PContext, n: PNode, flags: TExprFlags; expectedType: PType
 
   if t == nil:
     return localErrorNode(c, result, "object constructor needs an object type")
-  
+
   if t.skipTypes({tyGenericInst,
       tyAlias, tySink, tyOwned, tyRef}).kind != tyObject and
       expectedType != nil and expectedType.skipTypes({tyGenericInst,