[irgen-prepare] Clean up the pass and only invalidate analyzes if we actually change something.

rdar://39335800

Author: gottesmm

lib/SILOptimizer/Mandatory/IRGenPrepare.cpp

@@ -9,10 +9,15 @@
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 //
 //===----------------------------------------------------------------------===//
-//
-// Cleanup SIL to make it suitable for IRGen. Specifically, removes the calls to
-// Builtin.staticReport(), which are not needed post SIL.
-//
+///
+/// \file
+///
+/// Cleanup SIL to make it suitable for IRGen.
+///
+/// We perform the following canonicalizations:
+///
+/// 1. We remove calls to Builtin.staticReport(), which are not needed post SIL.
+///
 //===----------------------------------------------------------------------===//
 
 #include "swift/SILOptimizer/PassManager/Passes.h"
@@ -24,38 +29,52 @@
 
 using namespace swift;
 
-static void cleanFunction(SILFunction &Fn) {
-  for (auto &BB : Fn) {
-    auto I = BB.begin(), E = BB.end();
-    while (I != E) {
+static bool cleanFunction(SILFunction &fn) {
+  bool madeChange = false;
+
+  for (auto &bb : fn) {
+    for (auto i = bb.begin(), e = bb.end(); i != e;) {
       // Make sure there is no iterator invalidation if the inspected
       // instruction gets removed from the block.
-      SILInstruction *Inst = &*I;
-      ++I;
+      SILInstruction *inst = &*i;
+      ++i;
 
       // Remove calls to Builtin.staticReport().
-      if (auto *BI = dyn_cast<BuiltinInst>(Inst)) {
-        const BuiltinInfo &B = BI->getBuiltinInfo();
-        if (B.ID == BuiltinValueKind::StaticReport) {
-          // The call to the builtin should get removed before we reach
-          // IRGen.
-          recursivelyDeleteTriviallyDeadInstructions(BI, /* Force */true);
-        }
+      auto *bi = dyn_cast<BuiltinInst>(inst);
+      if (!bi) {
+        continue;
       }
+
+      const BuiltinInfo &bInfo = bi->getBuiltinInfo();
+      if (bInfo.ID != BuiltinValueKind::StaticReport) {
+        continue;
+      }
+
+      // The call to the builtin should get removed before we reach
+      // IRGen.
+      recursivelyDeleteTriviallyDeadInstructions(bi, /* Force */ true);
+      madeChange = true;
     }
   }
+
+  return madeChange;
 }
 
+//===----------------------------------------------------------------------===//
+//                            Top Level Entrypoint
+//===----------------------------------------------------------------------===//
+
 namespace {
-class IRGenPrepare : public swift::SILFunctionTransform {
 
-  /// The entry point to the transformation.
+class IRGenPrepare : public SILFunctionTransform {
   void run() override {
-    cleanFunction(*getFunction());
-    invalidateAnalysis(SILAnalysis::InvalidationKind::FunctionBody);
+    bool shouldInvalidate = cleanFunction(*getFunction());
+    if (!shouldInvalidate)
+      return;
+    invalidateAnalysis(SILAnalysis::InvalidationKind::Instructions);
   }
-
 };
+
 } // end anonymous namespace