[TypeSize] Inline conversion to uint64_t (NFC) (llvm#157454)

After llvm#156336 this cast operator has become trivial, so inline it into
the header. This is a minor compile-time improvement.

Author: nikic

llvm/include/llvm/Support/TypeSize.h

@@ -16,6 +16,7 @@
 #define LLVM_SUPPORT_TYPESIZE_H
 
 #include "llvm/Support/Compiler.h"
+#include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -371,7 +372,14 @@ class TypeSize : public details::FixedOrScalableQuantity<TypeSize, uint64_t> {
   //     else
   //       bail out early for scalable vectors and use getFixedValue()
   //   }
-  LLVM_ABI operator ScalarTy() const;
+  operator ScalarTy() const {
+    if (isScalable()) {
+      reportFatalInternalError(
+          "Cannot implicitly convert a scalable size to a fixed-width size in "
+          "`TypeSize::operator ScalarTy()`");
+    }
+    return getFixedValue();
+  }
 
   // Additional operators needed to avoid ambiguous parses
   // because of the implicit conversion hack.

llvm/lib/Support/CMakeLists.txt

@@ -265,7 +265,6 @@ add_llvm_component_library(LLVMSupport
   ToolOutputFile.cpp
   TrieRawHashMap.cpp
   Twine.cpp
-  TypeSize.cpp
   Unicode.cpp
   UnicodeCaseFold.cpp
   UnicodeNameToCodepoint.cpp