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.

5 files changed, 14 insertions, 11 deletions

diff --git a/lib/system/ansi_c.nim b/lib/system/ansi_c.nim
index a8a4bd767..be931ed14 100644
--- a/lib/system/ansi_c.nim
+++ b/lib/system/ansi_c.nim
@@ -224,7 +224,7 @@ proc rawWriteString*(f: CFilePtr, s: cstring, length: int) {.compilerproc, nonRe
 
 proc rawWrite*(f: CFilePtr, s: cstring) {.compilerproc, nonReloadable, inline.} =
   # we cannot throw an exception here!
-  discard c_fwrite(s, 1, cast[csize_t](s.len), f)
+  discard c_fwrite(s, 1, c_strlen(s), f)
   discard c_fflush(f)
 
 {.pop.}
diff --git a/lib/system/cgprocs.nim b/lib/system/cgprocs.nim
index 9d0d248c3..9a7645f9b 100644
--- a/lib/system/cgprocs.nim
+++ b/lib/system/cgprocs.nim
@@ -8,13 +8,3 @@
 #
 
 # Headers for procs that the code generator depends on ("compilerprocs")
-
-type
-  LibHandle = pointer       # private type
-  ProcAddr = pointer        # library loading and loading of procs:
-
-proc nimLoadLibrary(path: string): LibHandle {.compilerproc, hcrInline, nonReloadable.}
-proc nimUnloadLibrary(lib: LibHandle) {.compilerproc, hcrInline, nonReloadable.}
-proc nimGetProcAddr(lib: LibHandle, name: cstring): ProcAddr {.compilerproc, hcrInline, nonReloadable.}
-
-proc nimLoadLibraryError(path: string) {.compilerproc, hcrInline, nonReloadable.}
diff --git a/lib/system/memory.nim b/lib/system/memory.nim
index ebda60d8d..156773c48 100644
--- a/lib/system/memory.nim
+++ b/lib/system/memory.nim
@@ -43,6 +43,7 @@ proc nimCmpMem*(a, b: pointer, size: Natural): cint {.compilerproc, nonReloadabl
       inc i
 
 proc nimCStrLen*(a: cstring): int {.compilerproc, nonReloadable, inline.} =
+  if a.isNil: return 0
   when useLibC:
     cast[int](c_strlen(a))
   else:
diff --git a/lib/system/strmantle.nim b/lib/system/strmantle.nim
index 60c63501c..89046253b 100644
--- a/lib/system/strmantle.nim
+++ b/lib/system/strmantle.nim
@@ -23,6 +23,14 @@ proc cmpStrings(a, b: string): int {.inline, compilerproc.} =
   else:
     result = alen - blen
 
+proc leStrings(a, b: string): bool {.inline, compilerproc.} =
+  # required by upcoming backends (NIR).
+  cmpStrings(a, b) <= 0
+
+proc ltStrings(a, b: string): bool {.inline, compilerproc.} =
+  # required by upcoming backends (NIR).
+  cmpStrings(a, b) < 0
+
 proc eqStrings(a, b: string): bool {.inline, compilerproc.} =
   let alen = a.len
   let blen = b.len
diff --git a/lib/system/strs_v2.nim b/lib/system/strs_v2.nim
index abdbcd7c3..e79a2b324 100644
--- a/lib/system/strs_v2.nim
+++ b/lib/system/strs_v2.nim
@@ -201,6 +201,10 @@ proc prepareMutation*(s: var string) {.inline.} =
     let s = unsafeAddr s
     nimPrepareStrMutationV2(cast[ptr NimStringV2](s)[])
 
+proc nimAddStrV1(s: var NimStringV2; src: NimStringV2) {.compilerRtl, inl.} =
+  #if (s.p == nil) or (s.len+1 > s.p.cap and not strlitFlag):
+  prepareAdd(s, src.len)
+  appendString s, src
 
 func capacity*(self: string): int {.inline.} =
   ## Returns the current capacity of the string.