SSO for strings (#25593)

lib/std/formatfloat.nim

@@ -19,7 +19,12 @@ proc addCstringN(result: var string, buf: cstring; buflen: int) =
   let oldLen = result.len
   let newLen = oldLen + buflen
   result.setLen newLen
-  c_memcpy(result[oldLen].addr, buf, buflen.csize_t)
+  {.cast(noSideEffect).}:
+    when declared(completeStore):
+      c_memcpy(beginStore(result, buflen, oldLen), buf, buflen.csize_t)
+      endStore(result)
+    else:
+      discard c_memcpy(result[oldLen].addr, buf, buflen.csize_t)
 
 import std/private/[dragonbox, schubfach]
 

lib/std/private/digitsutils.nim

@@ -52,7 +52,7 @@ func addChars[T](result: var string, x: T, start: int, n: int) {.inline, enforce
     for i in 0..<n: result[old + i] = x[start + i]
   when nimvm: impl
   else:
-    when defined(js) or defined(nimscript): impl
+    when defined(js) or defined(nimscript) or defined(nimsso): impl
     else:
       {.noSideEffect.}:
         copyMem result[old].addr, x[start].unsafeAddr, n

lib/std/strbasics.nim

@@ -84,9 +84,9 @@ func setSlice*(s: var string, slice: Slice[int]) =
       when not declared(moveMem):
         impl()
       else:
-        when defined(nimSeqsV2):
-          prepareMutation(s)
-        moveMem(addr s[0], addr s[first], last - first + 1)
+        let p = beginStore(s, last - first + 1)
+        moveMem(p, addr p[first], last - first + 1)
+        endStore(s)
   s.setLen(last - first + 1)
 
 func strip*(a: var string, leading = true, trailing = true, chars: set[char] = whitespaces) {.inline.} =

lib/std/syncio.nim

@@ -485,7 +485,8 @@ proc readLine*(f: File, line: var string): bool {.tags: [ReadIOEffect],
     while true:
       # fixes #9634; this pattern may need to be abstracted as a template if reused;
       # likely other io procs need this for correctness.
-      fgetsSuccess = c_fgets(cast[cstring](addr line[pos]), sp.cint, f) != nil
+      fgetsSuccess = c_fgets(cast[cstring](beginStore(line, sp, pos)), sp.cint, f) != nil
+      endStore(line)
       if fgetsSuccess: break
       when not defined(nimscript):
         if errno == EINTR:
@@ -495,10 +496,11 @@ proc readLine*(f: File, line: var string): bool {.tags: [ReadIOEffect],
       checkErr(f)
       break
 
-    let m = c_memchr(addr line[pos], cint('\L'), cast[csize_t](sp))
+    let lineData = readRawData(line)
+    let m = c_memchr(addr lineData[pos], cint('\L'), cast[csize_t](sp))
     if m != nil:
       # \l found: Could be our own or the one by fgets, in any case, we're done
-      var last = cast[int](m) - cast[int](addr line[0])
+      var last = cast[int](m) - cast[int](lineData)
       if last > 0 and line[last-1] == '\c':
         line.setLen(last-1)
         return last > 1 or fgetsSuccess
@@ -564,7 +566,8 @@ proc readAllBuffer(file: File): string =
   result = ""
   var buffer = newString(BufSize)
   while true:
-    var bytesRead = readBuffer(file, addr(buffer[0]), BufSize)
+    var bytesRead = readBuffer(file, beginStore(buffer, BufSize), BufSize)
+    endStore(buffer)
     if bytesRead == BufSize:
       result.add(buffer)
     else:
@@ -590,7 +593,8 @@ proc readAllFile(file: File, len: int64): string =
   # We acquire the filesize beforehand and hope it doesn't change.
   # Speeds things up.
   result = newString(len)
-  let bytes = readBuffer(file, addr(result[0]), len)
+  let bytes = readBuffer(file, beginStore(result, len.int), len.int)
+  endStore(result)
   if endOfFile(file):
     if bytes.int64 < len:
       result.setLen(bytes)