Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -45,6 +45,8 @@
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/Option/ArgList.h"
+#include "llvm/Support/BLAKE3.h"
+#include "llvm/Support/Base64.h"
 #include "llvm/Support/CodeGen.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Compression.h"
@@ -2479,13 +2481,38 @@
     return;
   }
 
-  llvm::sys::path::append(
-      Path,
-      Twine(llvm::sys::path::filename(Input.getFilename())) + ".%%%%.json");
+  // Append the Input basename and a .XXXXXXXXXX.json suffix, where
+  // X is base64-ish and derived from the Input and Output filenames.
+  auto AppendBasenameAndHash = [](SmallString<256> &Path,
+                                  const InputInfo &Input,
+                                  const InputInfo &Output) {
+    llvm::TruncatedBLAKE3<8> Hash;
+    llvm::BLAKE3Result<8> HashResult;
+    Hash.update(llvm::StringRef(Input.getFilename()));
+    // Simpler value separation than that of HashBuilder, so external tools
+    // can deduce the filename easier:
+    Hash.update('\0');
+    Hash.update(llvm::StringRef(Output.getFilename()));
+    Hash.final(HashResult);
+
+    std::string Base64Hash = llvm::encodeBase64(HashResult);
+    // Base64: 8 * 1.33 (encoding efficiency) > 10
+    Base64Hash.resize(10);
+    // Make the base64 string filesystem and url safe by mapping + to -
+    // and / to _, see RFC 4648#section-5
+    for (char &c : Base64Hash) {
+      c = (c == '+') ? '-' : ((c == '/') ? '_' : c);
+    }
+    llvm::sys::path::append(
+        Path, Twine(llvm::sys::path::filename(Input.getFilename())) + "." +
+                  StringRef(Base64Hash) + ".json");
+  };
+
+  AppendBasenameAndHash(Path, Input, Output);
+
   int FD;
-  SmallString<256> TempPath;
-  Err = llvm::sys::fs::createUniqueFile(Path, FD, TempPath,
-                                        llvm::sys::fs::OF_Text);
+  Err = llvm::sys::fs::openFileForWrite(
+      Path, FD, llvm::sys::fs::CD_CreateAlways, llvm::sys::fs::OF_Text);
   if (Err) {
     Driver.Diag(diag::err_drv_compilationdatabase) << Path << Err.message();
     return;