Shuffle around some of the optimization passes.

The end goal here is to end up with a good pass ordering that will allow
us to only run one set of these passes, rather than running them
twice. This is a start in that direction.

No real impact measured on compile times as of this change. On
benchmarks I see a mix of regressions and improvements.

-O improvements:
  Calculator           -17.6%     1.21x
  Chars                -54.4%     2.19x
  PolymorphicCalls     -14.7%     1.17x
  SetIsSubsetOf        -14.1%     1.16x
  Sim2DArray           -14.1%     1.16x
  StrToInt             -30.4%     1.44x

-O regressions:
  CaptureProp          +32.9%     0.75x
  DictionarySwap       +36.0%     0.74x
  XorLoop              +39.8%     0.72x

-Ounchecked improvements:
  Chars                -58.0%     2.38x

-Ounchecked regressions:
  CaptureProp          +33.3%     0.75x

-Onone improvements:
  StrToInt             -14.9%     1.18x
  StringWalk           -47.6%     1.91x
  StringWithCString    -17.2%     1.21x
  (many more smaller improvements)

-Onone regressions:
  Calculator           +21.5%     0.82x
  OpenClose            +10.1%     0.91x

lib/SILOptimizer/PassManager/Passes.cpp

@@ -172,18 +172,52 @@ void AddHighLevelLoopOptPasses(SILPassManager &PM) {
   PM.addSwiftArrayOpts();
 }
 
+// Perform classic SSA optimizations.
 void AddSSAPasses(SILPassManager &PM, OptimizationLevelKind OpLevel) {
-  AddSimplifyCFGSILCombine(PM);
+  // Promote box allocations to stack allocations.
   PM.addAllocBoxToStack();
+
+  // Propagate copies through stack locations.  Should run after
+  // box-to-stack promotion since it is limited to propagating through
+  // stack locations. Should run before aggregate lowering since that
+  // splits up copy_addr.
   PM.addCopyForwarding();
+
+  // Split up opaque operations (copy_addr, retain_value, etc.).
   PM.addLowerAggregateInstrs();
-  PM.addSILCombine();
+
+  // Split up operations on stack-allocated aggregates (struct, tuple).
   PM.addSROA();
+
+  // Promote stack allocations to values.
   PM.addMem2Reg();
 
-  // Perform classic SSA optimizations.
+  // Run the devirtualizer, specializer, and inliner. If any of these
+  // makes a change we'll end up restarting the function passes on the
+  // current function (after optimizing any new callees).
+  PM.addDevirtualizer();
+  PM.addGenericSpecializer();
+  switch (OpLevel) {
+    case OptimizationLevelKind::HighLevel:
+      // Does not inline functions with defined semantics.
+      PM.addEarlyInliner();
+      break;
+    case OptimizationLevelKind::MidLevel:
+      // Does inline semantics-functions (except "availability"), but not
+      // global-init functions.
+      PM.addPerfInliner();
       PM.addGlobalOpt();
       PM.addLetPropertiesOpt();
+      break;
+    case OptimizationLevelKind::LowLevel:
+      // Inlines everything
+      PM.addLateInliner();
+      break;
+  }
+
+  PM.addMem2Reg();
+  AddSimplifyCFGSILCombine(PM);
+
   PM.addPerformanceConstantPropagation();
   PM.addDCE();
   PM.addCSE();
@@ -203,26 +237,6 @@ void AddSSAPasses(SILPassManager &PM, OptimizationLevelKind OpLevel) {
 
   PM.addSILLinker();
 
-  // Run the devirtualizer, specializer, and inliner. If any of these
-  // makes a change we'll end up restarting the function passes on the
-  // current function (after optimizing any new callees).
-  PM.addDevirtualizer();
-  PM.addGenericSpecializer();
-  switch (OpLevel) {
-    case OptimizationLevelKind::HighLevel:
-      // Does not inline functions with defined semantics.
-      PM.addEarlyInliner();
-      break;
-    case OptimizationLevelKind::MidLevel:
-      // Does inline semantics-functions (except "availability"), but not
-      // global-init functions.
-      PM.addPerfInliner();
-      break;
-    case OptimizationLevelKind::LowLevel:
-      // Inlines everything
-      PM.addLateInliner();
-      break;
-  }
   PM.addSimplifyCFG();
   // Only hoist releases very late.
   if (OpLevel == OptimizationLevelKind::LowLevel)

test/SILOptimizer/devirt_single_module_in_multiple_files.swift

@@ -6,12 +6,12 @@ public func test() {
   e.evaluate(1)
 }
 
-// CHECK-LABEL: sil shared [transparent] [reabstraction_thunk] @_TTSf3cpfr69_TFFC38devirt_single_module_in_multiple_files9EvaluatorcFT_S0_U_FT_Si_n_n___TTRXFo__dSi_XFo_iT__iSi_
+// CHECK-LABEL: sil shared @_TFFC38devirt_single_module_in_multiple_files9Evaluatorc
 // CHECK: %{{.*}} = class_method %{{.*}} : $Problem1, #Problem1.run!1 : (Problem1) -> () -> Int , $@convention(method) (@guaranteed Problem1) -> Int
 // CHECK-NEXT: apply
 // CHECK: return
 
-// CHECK-LABEL: sil shared [transparent] [reabstraction_thunk] @_TTSf3cpfr70_TFFC38devirt_single_module_in_multiple_files9EvaluatorcFT_S0_U0_FT_Si_n_n___TTRXFo__dSi_XFo_iT__iSi_
+// CHECK-LABEL: sil shared @_TFFC38devirt_single_module_in_multiple_files9Evaluatorc
 // CHECK: %{{.*}} = class_method %{{.*}} : $Problem2, #Problem2.run!1 : (Problem2) -> () -> Int , $@convention(method) (@guaranteed Problem2) -> Int
 // CHECK-NEXT: apply
 // CHECK: return