[llvm] [Support] Inline some raw_ostream methods (PR #97703)

[Fangrui Song via llvm-commits]

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@@ -400,11 +411,36 @@ class raw_ostream {
   //===--------------------------------------------------------------------===//
 private:
   /// Install the given buffer and mode.
-  void SetBufferAndMode(char *BufferStart, size_t Size, BufferKind Mode);
+  void SetBufferAndMode(char *BufferStart, size_t Size, BufferKind Mode) {
+    assert(((Mode == BufferKind::Unbuffered && !BufferStart && Size == 0) ||
+            (Mode != BufferKind::Unbuffered && BufferStart && Size != 0)) &&
+           "stream must be unbuffered or have at least one byte");
+    // Make sure the current buffer is free of content (we can't flush here; the
+    // child buffer management logic will be in write_impl).
+    assert(GetNumBytesInBuffer() == 0 && "Current buffer is non-empty!");
+
+    if (BufferMode == BufferKind::InternalBuffer)
+      delete[] OutBufStart;
+    OutBufStart = BufferStart;
+    OutBufEnd = OutBufStart + Size;
+    OutBufCur = OutBufStart;
+    BufferMode = Mode;
+
+    assert(OutBufStart <= OutBufEnd && "Invalid size!");
+  }
 
   /// Flush the current buffer, which is known to be non-empty. This outputs the
   /// currently buffered data and resets the buffer to empty.
-  void flush_nonempty();
+  void flush_nonempty() {
+    assert(OutBufCur > OutBufStart && "Invalid call to flush_nonempty.");
+    size_t Length = OutBufCur - OutBufStart;
+    OutBufCur = OutBufStart;
+    write_impl(OutBufStart, Length);
+  }
+
+  /// Slow path for writing when buffer is too small.
+  void writeSlow(unsigned char C);
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MaskRay wrote:

`writeSlow` returning `*this` might allow tail call optimization, but I don't know whether it makes a difference on code size...

https://github.com/llvm/llvm-project/pull/97703