Support: Avoid using SmallVector::set_size()

[dexonsmith]

Summary

Update platform-independent code in Support to stop using
SmallVector::set_size().

• For sys::path, descrease size using truncate() instead of set_size().
• For zlib, replace two pairs of reserve() / set_size() with resize_for_overwrite() and truncate().

See also Unix- and Windows-specific patches at:

• https://reviews.llvm.org/D115389
• https://reviews.llvm.org/D115390

Depends on https://reviews.llvm.org/D115383 or successor; blocker for https://reviews.llvm.org/D115380.

[dblaikie]

Probably worth committing separately in case either causes breakage.

[dexonsmith]

In D115391#3180980, @dblaikie wrote:

Probably worth committing separately in case either causes breakage.

Thanks for the review! Committed separately as 7df18557791ea1cf8f4f55d97d47ff5008f3bbbb and cd7bc0e010a3c0b4eb349e8c9a0e7edd591a5fff.

Just thinking now it'd have been better to push separately too -- likely you were implying that -- but at least now they're separately revertible.

[dblaikie]

In D115391#3181442, @dexonsmith wrote:

In D115391#3180980, @dblaikie wrote:

Probably worth committing separately in case either causes breakage.

Thanks for the review! Committed separately as 7df18557791ea1cf8f4f55d97d47ff5008f3bbbb and cd7bc0e010a3c0b4eb349e8c9a0e7edd591a5fff.

Just thinking now it'd have been better to push separately too -- likely you were implying that -- but at least now they're separately revertible.

Yeah - can be good to space them out so they get separate runs through CI - I don't always remember to do this either.

llvm/lib/Support/Path.cpp

StringRef parent_path(StringRef path, Style style) {
   if (end_pos == StringRef::npos)
     return StringRef();
   return path.substr(0, end_pos);
 }
 
 void remove_filename(SmallVectorImpl<char> &path, Style style) {
   size_t end_pos = parent_path_end(StringRef(path.begin(), path.size()), style);
   if (end_pos != StringRef::npos)
-    path.set_size(end_pos);
+    path.truncate(end_pos);
 }
 
 void replace_extension(SmallVectorImpl<char> &path, const Twine &extension,
                        Style style) {
   StringRef p(path.begin(), path.size());
   SmallString<32> ext_storage;
   StringRef ext = extension.toStringRef(ext_storage);
 
   // Erase existing extension.
   size_t pos = p.find_last_of('.');
   if (pos != StringRef::npos && pos >= filename_pos(p, style))
-    path.set_size(pos);
+    path.truncate(pos);
 
   // Append '.' if needed.
   if (ext.size() > 0 && ext[0] != '.')
     path.push_back('.');
 
   // Append extension.
   path.append(ext.begin(), ext.end());
 }