[SIL Optimization] Add a new mandatory pass for unrolling forEach

calls over arrays created from array literals. This enables optimizing
further the output of the OSLogOptimization pass, and results in
highly-compact and optimized IR for calls to the new os log API.

<rdar://58928427>

Author: ravikandhadai

include/swift/AST/SemanticAttrs.def

@@ -60,6 +60,8 @@ SEMANTICS_ATTR(ARRAY_COUNT, "array.count")
 SEMANTICS_ATTR(ARRAY_DEALLOC_UNINITIALIZED, "array.dealloc_uninitialized")
 SEMANTICS_ATTR(ARRAY_UNINITIALIZED_INTRINSIC, "array.uninitialized_intrinsic")
 
+SEMANTICS_ATTR(SEQUENCE_FOR_EACH, "sequence.forEach")
+
 SEMANTICS_ATTR(OPTIMIZE_SIL_SPECIALIZE_GENERIC_NEVER, "optimize.sil.specialize.generic.never")
 SEMANTICS_ATTR(OPTIMIZE_SIL_SPECIALIZE_GENERIC_PARTIAL_NEVER,
           "optimize.sil.specialize.generic.partial.never")

include/swift/SILOptimizer/PassManager/Passes.def

@@ -319,6 +319,8 @@ PASS(NonInlinableFunctionSkippingChecker, "check-non-inlinable-function-skipping
 PASS(YieldOnceCheck, "yield-once-check",
     "Check correct usage of yields in yield-once coroutines")
 PASS(OSLogOptimization, "os-log-optimization", "Optimize os log calls")
+PASS(ForEachLoopUnroll, "for-each-loop-unroll",
+     "Unroll forEach loops over array literals")
 PASS(MandatoryCombine, "mandatory-combine",
     "Perform mandatory peephole combines")
 PASS(BugReducerTester, "bug-reducer-tester",

include/swift/SILOptimizer/Utils/InstOptUtils.h

@@ -145,6 +145,15 @@ class InstructionDeleter {
       SILInstruction *inst,
       llvm::function_ref<void(SILInstruction *)> callback =
                                     [](SILInstruction *) {});
+
+  /// Recursively visit users of \c inst  (including \c inst)and force delete
+  /// them. Also, destroy the consumed operands of the deleted instructions
+  /// whenever necessary. Invoke the \c callback on instructions that are
+  /// deleted.
+  void recursivelyForceDeleteUsersAndFixLifetimes(
+      SILInstruction *inst,
+      llvm::function_ref<void(SILInstruction *)> callback =
+          [](SILInstruction *) {});
 };
 
 /// If \c inst is dead, delete it and recursively eliminate all code that

lib/SILOptimizer/LoopTransforms/CMakeLists.txt

@@ -5,4 +5,5 @@ silopt_register_sources(
   LoopRotate.cpp
   LoopUnroll.cpp
   LICM.cpp
+  ForEachLoopUnroll.cpp
 )