Adds debug statements to ARM areInlineCompatible

This makes it easier to see why your function isn't getting inlined for.

Author: CrooseGit

llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp

@@ -102,6 +102,53 @@ bool ARMTTIImpl::areInlineCompatible(const Function *Caller,
   // the callers'.
   bool MatchSubset = ((CallerBits & CalleeBits) & InlineFeaturesAllowed) ==
                      (CalleeBits & InlineFeaturesAllowed);
+
+  LLVM_DEBUG({
+    dbgs() << "=== Inline compatibility debug ===\n";
+    dbgs() << "Caller: " << Caller->getName() << "\n";
+    dbgs() << "Callee: " << Callee->getName() << "\n";
+
+    // Bit diffs
+    FeatureBitset MissingInCaller = CalleeBits & ~CallerBits; // callee-only
+    FeatureBitset ExtraInCaller = CallerBits & ~CalleeBits;   // caller-only
+
+    // Counts
+    dbgs() << "Only-in-caller bit count: " << ExtraInCaller.count() << "\n";
+    dbgs() << "Only-in-callee bit count: " << MissingInCaller.count() << "\n";
+
+    dbgs() << "Only-in-caller feature indices [";
+    {
+      bool First = true;
+      for (size_t I = 0, E = ExtraInCaller.size(); I < E; ++I) {
+        if (ExtraInCaller.test(I)) {
+          if (!First)
+            dbgs() << ", ";
+          dbgs() << I;
+          First = false;
+        }
+      }
+    }
+    dbgs() << "]\n";
+
+    dbgs() << "Only-in-callee feature indices [";
+    {
+      bool First = true;
+      for (size_t I = 0, E = MissingInCaller.size(); I < E; ++I) {
+        if (MissingInCaller.test(I)) {
+          if (!First)
+            dbgs() << ", ";
+          dbgs() << I;
+          First = false;
+        }
+      }
+    }
+    dbgs() << "]\n";
+
+    // Indicies map to features as found in
+    // llvm-project/(your_build)/lib/Target/ARM/ARMGenSubtargetInfo.inc
+    dbgs() << "MatchExact=" << (MatchExact ? "true" : "false")
+           << " MatchSubset=" << (MatchSubset ? "true" : "false") << "\n";
+  });
   return MatchExact && MatchSubset;
 }