Do not inline self-recursive functions into other functions.

Because our optimization pipeline runs the inliner multiple times,
inlining self-recursive functions into other functions can result in
substantial code growth, which results in more code being generated, and
more compile time.

This was exposed by other changes I have to remove call graph updating
from the inliner (which should have resulted in NFC but didn't due to
implicit deserialization).

Author: rudkx

lib/SILPasses/IPO/PerformanceInliner.cpp

@@ -542,6 +542,16 @@ bool SILPerformanceInliner::hasInliningCycle(SILFunction *Caller,
   return InlinedBefore;
 }
 
+
+static bool calleeIsSelfRecursive(SILFunction *Callee) {
+  for (auto &BB : *Callee)
+    for (auto &I : BB)
+      if (auto Apply = FullApplySite::isa(&I))
+        if (Apply.getCalleeFunction() == Callee)
+          return true;
+  return false;
+}
+
 // Returns the callee of an apply_inst if it is basically inlinable.
 SILFunction *SILPerformanceInliner::getEligibleFunction(FullApplySite AI) {
 
@@ -624,6 +634,16 @@ SILFunction *SILPerformanceInliner::getEligibleFunction(FullApplySite AI) {
           Callee->getName() << ".\n");
     return nullptr;
   }
+
+  // Inlining self-recursive functions into other functions can result
+  // in excessive code duplication since we run the inliner multiple
+  // times in our pipeline.
+  if (calleeIsSelfRecursive(Callee)) {
+    DEBUG(llvm::dbgs() << "        FAIL: Callee is self-recursive in " <<
+          Callee->getName() << ".\n");
+    return nullptr;
+  }
+
   DEBUG(llvm::dbgs() << "        Eligible callee: " <<
         Callee->getName() << "\n");
 

test/SILPasses/inline_recursive.swift

@@ -7,13 +7,17 @@ private func recFunc(x: Int) -> Int {
   return 0
 }
 
-//CHECK-LABEL: sil {{.*}}callit
-// CHECK: bb0:
-// CHECK-NEXT: integer_literal {{.*}}, 0
-// CHECK-NEXT: struct
-// CHECK-NEXT: return
+// Ensure that we do not inline self-recursive functions into other
+// functions since doing so can result in large code growth if we run
+// the inlining pass multiple times.
 
+// CHECK-LABEL: sil hidden @_TF16inline_recursive6callitFT_Si
+// CHECK: bb0:
+// CHECK: [[FN:%.*]] = function_ref @_TF16inline_recursiveP33_38E63D320CFF538A1F98BBC31453B1EB7recFuncFSiSi
+// CHECK: [[BUILTIN_INT:%.*]] = integer_literal $Builtin.Int64, 3
+// CHECK: [[INT:%.*]] = struct $Int ([[BUILTIN_INT]] : $Builtin.Int64)
+// CHECK: [[APPLY:%.*]] = apply [[FN]]([[INT]])
+// CHECK: return [[APPLY]]
 func callit() -> Int {
   return recFunc(3)
 }
-