PerformanceInliner: protect against misuse of @inline(__always)

Inline-always should only be used on relatively small functions. It must not be used on recursive functions.
Add a check that prevents that inlining of large @inline(__always) functions.

#64319
rdar://106655649

Author: eeckstein

lib/SILOptimizer/Transforms/PerformanceInliner.cpp

@@ -619,12 +619,29 @@ static bool returnsClosure(SILFunction *F) {
   return false;
 }
 
+static bool hasMaxNumberOfBasicBlocks(SILFunction *f, int limit) {
+  for (SILBasicBlock &block : *f) {
+    (void)block;
+    if (limit == 0)
+      return false;
+    limit--;
+  }
+  return true;
+}
+
 static bool isInlineAlwaysCallSite(SILFunction *Callee) {
   if (Callee->isTransparent())
     return true;
-  if (Callee->getInlineStrategy() == AlwaysInline)
-    if (!Callee->getModule().getOptions().IgnoreAlwaysInline)
-      return true;
+  if (Callee->getInlineStrategy() == AlwaysInline &&
+      !Callee->getModule().getOptions().IgnoreAlwaysInline &&
+
+      // Protect against misuse of @inline(__always).
+      // Inline-always should only be used on relatively small functions.
+      // It must not be used on recursive functions. This check prevents that
+      // the compiler blows up if @inline(__always) is put on a recursive function.
+      hasMaxNumberOfBasicBlocks(Callee, 100)) {
+    return true;
+  }
   return false;
 }