[Support] mapped_file_region: store size as size_t

Summary:
Found when testing stage-2 build with D38101.

```
In file included from /build/llvm/lib/Support/Path.cpp:1045:
/build/llvm/lib/Support/Unix/Path.inc:648:14: error: comparison 'uint64_t' (aka 'unsigned long') > 18446744073709551615 is always false [-Werror,-Wtautological-constant-compare]
  if (length > std::numeric_limits<size_t>::max()) {
      ~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

`size_t` is `uint64_t` here, apparently, thus any `uint64_t` value
always fits into `size_t`.

Initial patch was to use some preprocessor logic to
not check if the size is known to fit at compile time.
But Zachary Turner suggested using this approach.

Reviewers: Bigcheese, rafael, zturner, mehdi_amini

Reviewed by (via email): zturner

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D38132

llvm-svn: 314312

1 files changed, 3 insertions, 3 deletions

diff --git a/llvm/include/llvm/Support/FileSystem.h b/llvm/include/llvm/Support/FileSystem.h
index 8b74d766ebe..e8460ca0a31 100644
--- a/llvm/include/llvm/Support/FileSystem.h
+++ b/llvm/include/llvm/Support/FileSystem.h
@@ -745,7 +745,7 @@ public:
 
 private:
   /// Platform-specific mapping state.
-  uint64_t Size;
+  size_t Size;
   void *Mapping;
 
   std::error_code init(int FD, uint64_t Offset, mapmode Mode);
@@ -758,12 +758,12 @@ public:
   /// \param fd An open file descriptor to map. mapped_file_region takes
   ///   ownership if closefd is true. It must have been opended in the correct
   ///   mode.
-  mapped_file_region(int fd, mapmode mode, uint64_t length, uint64_t offset,
+  mapped_file_region(int fd, mapmode mode, size_t length, uint64_t offset,
                      std::error_code &ec);
 
   ~mapped_file_region();
 
-  uint64_t size() const;
+  size_t size() const;
   char *data() const;
 
   /// Get a const view of the data. Modifying this memory has undefined