[clang] [clang] Specialize invocation path visitation to the cow (PR #205686)

[Ben Langmuir via cfe-commits]

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@@ -5354,108 +5354,87 @@ std::string CompilerInvocation::computeContextHash() const {
   return toString(llvm::APInt(64, Hash), 36, /*Signed=*/false);
 }
 
-void CompilerInvocationBase::visitPathsImpl(
-    llvm::function_ref<bool(std::string &)> Predicate) {
-#define RETURN_IF(PATH)                                                        \
+void CowCompilerInvocation::visitMutPaths(
+    llvm::function_ref<VisitMutResult(StringRef, std::string &)> Cb) {
+  std::string NewValue;
+
+#define RETURN_IF(OPTS, PATH)                                                  \
   do {                                                                         \
-    if (Predicate(PATH))                                                       \
+    VisitMutResult Res = Cb(PATH, NewValue);                                   \
+    if (Res.Replace) {                                                         \
+      (void)ensureOwned(OPTS);                                                 \
+      PATH = "";                                                               \
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benlangmuir wrote:

This is very minor, but `.clear()` optimizes better than assignment to empty string. Despite the compiler being able to detect the string has length 0 it still ends up calling out to library functions.

https://github.com/llvm/llvm-project/pull/205686