[clang] [Modules] No transitive source location change (PR #86912)

[Michael Spencer via cfe-commits]

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@@ -149,14 +157,44 @@ class SourceLocationSequence::State {
   operator SourceLocationSequence *() { return &Seq; }
 };
 
-inline uint64_t SourceLocationEncoding::encode(SourceLocation Loc,
-                                               SourceLocationSequence *Seq) {
-  return Seq ? Seq->encode(Loc) : encodeRaw(Loc.getRawEncoding());
+inline SourceLocationEncoding::RawLocEncoding
+SourceLocationEncoding::encode(SourceLocation Loc, UIntTy BaseOffset,
+                               unsigned BaseModuleFileIndex,
+                               SourceLocationSequence *Seq) {
+  // If the source location is a local source location, we can try to optimize
+  // the similar sequences to only record the differences.
+  if (!BaseOffset)
+    return Seq ? Seq->encode(Loc) : encodeRaw(Loc.getRawEncoding());
+
+  if (Loc.isInvalid())
+    return 0;
+  
+  // Otherwise, the higher bits are used to store the module file index,
+  // so it is meaningless to optimize the source locations into small
+  // integers. Let's try to always use the raw encodings.
+  assert(Loc.getOffset() >= BaseOffset);
+  Loc = Loc.getLocWithOffset(-BaseOffset);
+  RawLocEncoding Encoded = encodeRaw(Loc.getRawEncoding());
+  assert(Encoded < ((RawLocEncoding)1 << 32));
+
+  assert(BaseModuleFileIndex < ((RawLocEncoding)1 << 32));
+  Encoded |= (RawLocEncoding)BaseModuleFileIndex << 32;
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Bigcheese wrote:

Were you going to change this to only reserve 16 bits for module index?

https://github.com/llvm/llvm-project/pull/86912