MandatoryPerformanceOptimizations: run DeadStoreElimination for global init functions.

Cleanup leftovers from simplification.
The InitializeStaticGlobals pass cannot deal with dead stores in global init functions.

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/DeadStoreElimination.swift

@@ -53,6 +53,10 @@ import SIL
 let deadStoreElimination = FunctionPass(name: "dead-store-elimination") {
   (function: Function, context: FunctionPassContext) in
 
+  eliminateDeadStores(in: function, context)
+}
+
+func eliminateDeadStores(in function: Function, _ context: FunctionPassContext) {
   // Avoid quadratic complexity by limiting the number of visited instructions.
   // This limit is sufficient for most "real-world" functions, by far.
   var complexityBudget = 10_000

SwiftCompilerSources/Sources/Optimizer/ModulePasses/MandatoryPerformanceOptimizations.swift

@@ -219,6 +219,12 @@ private func optimize(function: Function, _ context: FunctionPassContext, _ modu
 
     changed = context.eliminateDeadAllocations(in: function) || changed
   }
+
+  if function.isGlobalInitOnceFunction {
+    // Cleanup leftovers from simplification. The InitializeStaticGlobals pass cannot deal with dead
+    // stores in global init functions.
+    eliminateDeadStores(in: function, context)
+  }
 }
 
 private func inlineAndDevirtualize(apply: FullApplySite, alreadyInlinedFunctions: inout Set<PathFunctionTuple>,

test/SILOptimizer/mandatory_performance_optimizations.sil

@@ -15,6 +15,7 @@ struct NonTrivialStruct {
 
 sil_global [let] @g1 : $Int32
 sil_global [let] @g2 : $Int32
+sil_global [let] @g3 : $Int32
 
 sil @paable : $@convention(thin) (Builtin.Int64) -> ()
 sil @moved_pai_callee : $@convention(thin) (@inout_aliasable Builtin.Int64) -> ()
@@ -161,6 +162,25 @@ bb0:
   return %6 : $()
 }
 
+// CHECK-LABEL: sil [global_init_once_fn] [no_locks] [perf_constraint] [ossa] @remove_loads_and_stores_in_globalinit :
+// CHECK-NOT:     store
+// CHECK:         debug_step
+// CHECK-NOT:     load
+// CHECK:       } // end sil function 'remove_loads_and_stores_in_globalinit'
+sil [global_init_once_fn] [no_locks] [ossa] @remove_loads_and_stores_in_globalinit : $@convention(c) () -> () {
+bb0:
+  alloc_global @g3
+  %1 = global_addr @g3 : $*Int32
+  %2 = integer_literal $Builtin.Int32, 10
+  %3 = struct $Int32 (%2)
+  store %3 to [trivial] %1
+  debug_step
+  %6 = load [trivial] %1
+  store %6 to [trivial] %1
+  %r = tuple ()
+  return %r
+}
+
 // Check that we don't crash on global init-once declarations.
 
 // CHECK-LABEL: sil [global_init_once_fn] [no_locks] @external_global_init_once : $@convention(c) () -> ()

test/SILOptimizer/performance-annotations.swift

@@ -22,7 +22,7 @@ struct Str : P {
     return a + x
   }
 
-  static let s = 27
+  static let s = 27 << 0
   static var s2 = 10 + s
   static var s3 = initFunc() // expected-error {{global/static variable initialization can cause locking}}
 }