[clang] [clang] Delete duplicate code in sourcemanager (PR #166236)

[Aaron Ballman via cfe-commits]

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@@ -1275,43 +1275,24 @@ class SourceManager : public RefCountedBase<SourceManager> {
   /// start of the buffer of the location.
   FileIDAndOffset getDecomposedLoc(SourceLocation Loc) const {
     FileID FID = getFileID(Loc);
-    auto *Entry = getSLocEntryOrNull(FID);
-    if (!Entry)
-      return std::make_pair(FileID(), 0);
-    return std::make_pair(FID, Loc.getOffset() - Entry->getOffset());
+    const SrcMgr::SLocEntry &Entry = getSLocEntry(FID);
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AaronBallman wrote:

> Do you think that there could be non 0 Loc.offset value when FID is invalid?

Maybe yes, in two ways. 1) for normal compilation paths, I'm not 100% sure but I thought we use a memory buffer for things defined on the command line, so that would have an invalid file ID but potentially have a nonzero offset, but I could be remembering incorrectly. That's a case worth testing. 2) calls to the function happening within a debugger when the state of things may not be correct (e.g., someone is trying to debug a modules bug where the file ID isn't properly loaded for some reason and now they get odd behavior because it's a valid source location entry.)

It may be worth checking a blame to see whether this is intentional behavior we were checking for or whether this was someone being defensive. If it's defensive coding, then I think your changes make sense; but if this is intentional, it'd be good to understand the situation.

https://github.com/llvm/llvm-project/pull/166236