BooleanLiteralFolding: remove dead blocks

Remove all dead blocks which are a result of constant folding condition branches

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/BooleanLiteralFolding.swift

@@ -46,25 +46,30 @@ import SIL
 let booleanLiteralFolding = FunctionPass(name: "boolean-literal-folding") {
   (function: Function, context: FunctionPassContext) in
 
+  var changed = false
   for block in function.blocks {
     if let condBr = block.terminator as? CondBranchInst {
-      fold(condBranch: condBr, context)
+      changed = fold(condBranch: condBr, context) || changed
     }
   }
+  if changed {
+    _ = context.removeDeadBlocks(in: function)
+  }
 }
 
-private func fold(condBranch: CondBranchInst, _ context: FunctionPassContext) {
+private func fold(condBranch: CondBranchInst, _ context: FunctionPassContext) -> Bool {
   guard let structExtract = condBranch.condition as? StructExtractInst,
         let initApply = structExtract.struct as? ApplyInst,
         initApply.hasSemanticsAttribute("bool.literal_init"),
         initApply.arguments.count == 2,
         let literal = initApply.arguments[0] as? IntegerLiteralInst,
         let literalValue = literal.value else
   {
-    return
+    return false
   }
 
   let builder = Builder(before: condBranch, context)
   builder.createBranch(to: literalValue == 0 ? condBranch.falseBlock : condBranch.trueBlock)
   context.erase(instruction: condBranch)
+  return true
 }

test/SILOptimizer/boolean-literal-folding.sil

@@ -15,6 +15,9 @@ sil public_external [_semantics "bool.literal_init"] @wrong_bool_literal_init :
 // CHECK:         struct_extract
 // CHECK-NEXT:    br bb1
 // CHECK:       bb1:
+// CHECK-NEXT:    debug_step
+// CHECK-NEXT:    br bb2
+// CHECK-NOT:   bb3
 // CHECK:       } // end sil function 'replace_true'
 sil [ossa] @replace_true : $@convention(thin) () -> () {
 bb0:
@@ -25,6 +28,7 @@ bb0:
   %4 = struct_extract %3 : $Bool, #Bool._value
   cond_br %4, bb1, bb2
 bb1:
+  debug_step
   br bb3
 bb2:
   br bb3
@@ -35,8 +39,10 @@ bb3:
 
 // CHECK-LABEL: sil [ossa] @replace_false :
 // CHECK:         struct_extract
-// CHECK-NEXT:    br bb2
+// CHECK-NEXT:    br bb1
 // CHECK:       bb1:
+// CHECK-NEXT:    br bb2
+// CHECK-NOT:   bb3
 // CHECK:       } // end sil function 'replace_false'
 sil [ossa] @replace_false : $@convention(thin) () -> () {
 bb0:
@@ -47,6 +53,7 @@ bb0:
   %4 = struct_extract %3 : $Bool, #Bool._value
   cond_br %4, bb1, bb2
 bb1:
+  debug_step
   br bb3
 bb2:
   br bb3

test/SILOptimizer/discard_checking.swift

@@ -33,15 +33,15 @@ struct Basics: ~Copyable {
     repeat {
       switch c {
       case .red:
-        fatalError("bah!") // expected-error {{must consume 'self' before exiting method that discards self}}
+        fatalError("bah!")
       case .blue:
-        throw E.someError // expected-error {{must consume 'self' before exiting method that discards self}}
+        throw E.someError
       case .green:
         self = Basics()
       default: print("hi")
       }
     } while true
-    discard self // expected-note 2{{discarded self here}}
+    discard self
   }
 
   consuming func test2_fixed(_ c: Color) throws {