Swift Optimizer: add simplification for cond_fail

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/CMakeLists.txt

@@ -12,6 +12,7 @@ swift_compiler_sources(Optimizer
   SimplifyBranch.swift
   SimplifyBuiltin.swift
   SimplifyCondBranch.swift
+  SimplifyCondFail.swift
   SimplifyGlobalValue.swift
   SimplifyStrongRetainRelease.swift
   SimplifyStructExtract.swift

SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyCondFail.swift

@@ -0,0 +1,29 @@
+//===--- SimplifyCondFail.swift -------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SIL
+
+extension CondFailInst : OnoneSimplifyable {
+  func simplify(_ context: SimplifyContext) {
+
+    /// Eliminates
+    /// ```
+    ///   %0 = integer_literal 0
+    ///   cond_fail %0, "message"
+    /// ```
+    if let literal = condition as? IntegerLiteralInst,
+       literal.value.isZero() {
+
+      context.erase(instruction: self)
+    }
+  }
+}

test/SILOptimizer/simplify_cond_fail.sil

@@ -0,0 +1,39 @@
+// RUN: %target-sil-opt -enable-sil-verify-all %s -onone-simplification -simplify-instruction=cond_fail | %FileCheck %s
+
+// REQUIRES: swift_in_compiler
+
+import Swift
+import Builtin
+
+// CHECK-LABEL: sil @not_failing
+// CHECK-NOT:     cond_fail
+// CHECK:       } // end sil function 'not_failing'
+sil @not_failing : $@convention(thin) () -> () {
+bb0:
+  %0 = integer_literal $Builtin.Int1, 0
+  cond_fail %0 : $Builtin.Int1, "not failing"
+  %r = tuple ()
+  return %r : $()
+}
+
+// CHECK-LABEL: sil @failing
+// CHECK:         cond_fail
+// CHECK:       } // end sil function 'failing'
+sil @failing : $@convention(thin) () -> () {
+bb0:
+  %0 = integer_literal $Builtin.Int1, -1
+  cond_fail %0 : $Builtin.Int1, "failing"
+  %r = tuple ()
+  return %r : $()
+}
+
+// CHECK-LABEL: sil @unknown
+// CHECK:         cond_fail
+// CHECK:       } // end sil function 'unknown'
+sil @unknown : $@convention(thin) (Builtin.Int1) -> () {
+bb0(%0 : $Builtin.Int1):
+  cond_fail %0 : $Builtin.Int1, "unknown"
+  %r = tuple ()
+  return %r : $()
+}
+