[ownership] Add a frontend option to stop optimizing right before we lower ownership.

Specifically the option: -sil-stop-optzns-before-lowering-ownership. This makes
it possible to write end-to-end tests on OSSA passes. Before one would have to
pattern match after ownership was lowered, losing the ability to do finegrained
FileCheck pattern matching on ossa itself.

Author: gottesmm

include/swift/AST/SILOptions.h

@@ -81,6 +81,10 @@ class SILOptions {
   /// Whether to stop the optimization pipeline after serializing SIL.
   bool StopOptimizationAfterSerialization = false;
 
+  /// Whether to stop the optimization pipeline right before we lower ownership
+  /// and go from OSSA to non-ownership SIL.
+  bool StopOptimizationBeforeLoweringOwnership = false;
+
   /// Whether to skip emitting non-inlinable function bodies.
   bool SkipNonInlinableFunctionBodies = false;
 

include/swift/Option/FrontendOptions.td

@@ -580,6 +580,11 @@ def sil_debug_serialization : Flag<["-"], "sil-debug-serialization">,
   HelpText<"Do not eliminate functions in Mandatory Inlining/SILCombine dead "
            "functions. (for debugging only)">;
 
+def sil_stop_optzns_before_lowering_ownership :
+  Flag<["-"], "sil-stop-optzns-before-lowering-ownership">,
+  HelpText<"Stop optimizing at SIL time before we lower ownership from SIL. "
+           "Intended only for SIL ossa tests">;
+
 def print_inst_counts : Flag<["-"], "print-inst-counts">,
   HelpText<"Before IRGen, count all the various SIL instructions. Must be used "
            "in conjunction with -print-stats.">;

lib/Frontend/CompilerInvocation.cpp

@@ -1148,6 +1148,8 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
   Opts.EmitVerboseSIL |= Args.hasArg(OPT_emit_verbose_sil);
   Opts.EmitSortedSIL |= Args.hasArg(OPT_emit_sorted_sil);
   Opts.PrintInstCounts |= Args.hasArg(OPT_print_inst_counts);
+  Opts.StopOptimizationBeforeLoweringOwnership |=
+      Args.hasArg(OPT_sil_stop_optzns_before_lowering_ownership);
   if (const Arg *A = Args.getLastArg(OPT_external_pass_pipeline_filename))
     Opts.ExternalPassPipelineFilename = A->getValue();
 

lib/SILOptimizer/PassManager/PassPipeline.cpp

@@ -447,6 +447,9 @@ static void addPerfEarlyModulePassPipeline(SILPassPipelinePlan &P) {
   //
   // This is done so we can push ownership through the pass pipeline first for
   // the stdlib and then everything else.
+  if (P.getOptions().StopOptimizationBeforeLoweringOwnership)
+    return;
+
   P.addNonStdlibNonTransparentFunctionOwnershipModelEliminator();
 
   // Start by linking in referenced functions from other modules.
@@ -721,14 +724,21 @@ SILPassPipelinePlan::getPerformancePassPipeline(const SILOptions &Options) {
 
   // Eliminate immediately dead functions and then clone functions from the
   // stdlib.
+  //
+  // This also performs early OSSA based optimizations on *all* swift code.
   addPerfEarlyModulePassPipeline(P);
 
+  // Then if we were asked to stop optimization before lowering OSSA (causing us
+  // to exit early from addPerfEarlyModulePassPipeline), exit early.
+  if (P.getOptions().StopOptimizationBeforeLoweringOwnership)
+    return P;
+
   // Then run an iteration of the high-level SSA passes.
   //
   // FIXME: When *not* emitting a .swiftmodule, skip the high-level function
   // pipeline to save compile time.
   //
-  // NOTE: Ownership is now stripped within this function!
+  // NOTE: Ownership is now stripped within this function for the stdlib.
   addHighLevelFunctionPipeline(P);
 
   addHighLevelModulePipeline(P);