PerformanceDiagnostics: fix handling of infinite loops and change error handling

* Don't exclude code which end up in an infinite loop. rdar://116705459
* Don't exclude error handling code (throw, catch). Errors are existentials and will always allocate. Once we have typed throws it will be possible to do error handling without allocations.

Author: eeckstein

lib/SILOptimizer/Mandatory/PerformanceDiagnostics.cpp

@@ -157,12 +157,11 @@ bool PerformanceDiagnostics::visitFunction(SILFunction *function,
   if (!function->isDefinition())
     return false;
 
-  ReachingReturnBlocks rrBlocks(function);
-  NonErrorHandlingBlocks neBlocks(function);
-                                       
   for (SILBasicBlock &block : *function) {
-    if (!rrBlocks.reachesReturn(&block) || !neBlocks.isNonErrorHandling(&block))
+    // Exclude fatal-error blocks.
+    if (isa<UnreachableInst>(block.getTerminator()))
       continue;
+
     for (SILInstruction &inst : block) {
       if (visitInst(&inst, perfConstr, parentLoc))
         return true;

test/SILOptimizer/performance-annotations.swift

@@ -94,18 +94,18 @@ func testMemoryLayout() -> Int {
 class MyError : Error {}
 
 @_noLocks
-func noDiagnosticsInThrowPath(_ b: Bool) throws -> Int {
+func errorExistential(_ b: Bool) throws -> Int {
   if b {
     return 28
   }
-  throw MyError()
+  throw MyError()  // expected-error {{Using type 'MyError' can cause metadata allocation or locks}}
 }
 
 @_noLocks
-func noDiagnosticsInCatch(_ b: Bool) throws -> Int? {
+func testCatch(_ b: Bool) throws -> Int? {
   do {
-    return try noDiagnosticsInThrowPath(true)
-  } catch let e as MyError {
+    return try errorExistential(true)
+  } catch let e as MyError { // expected-error {{this code performs reference counting operations which can cause locking}}
     print(e)
     return nil
   }
@@ -405,3 +405,10 @@ func baz<T>(t: T) -> T {
 func nestedClosures() -> Int {
     return baz(t: 42)
 }
+
+@_noAllocation
+func testInfiniteLoop(_ c: Cl) {
+  c.classMethod() // expected-error {{called function is not known at compile time and can have unpredictable performance}}
+  while true {}
+}
+