[FormatVariadic] Reduce allocations

- Move Adapters array to the stack, we know the size precisely
- Parse format string on demand into a SmallVector. In theory this could
  lead to parsing it multiple times, but I couldn't find a single instance
  of that in LLVM.
- Make more of the implementation details private.

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/Support/FormatVariadic.cpp b/llvm/lib/Support/FormatVariadic.cpp
index 0d61fae..632e879 100644
--- a/llvm/lib/Support/FormatVariadic.cpp
+++ b/llvm/lib/Support/FormatVariadic.cpp
@@ -141,9 +141,9 @@ formatv_object_base::splitLiteralAndReplacement(StringRef Fmt) {
   return std::make_pair(ReplacementItem{Fmt}, StringRef());
 }
 
-std::vector<ReplacementItem>
+SmallVector<ReplacementItem, 2>
 formatv_object_base::parseFormatString(StringRef Fmt) {
-  std::vector<ReplacementItem> Replacements;
+  SmallVector<ReplacementItem, 2> Replacements;
   ReplacementItem I;
   while (!Fmt.empty()) {
     std::tie(I, Fmt) = splitLiteralAndReplacement(Fmt);