SILCombine: make it possible to add a Swift simplification to an existing SILCombine visit function.

So far a `SILCombineSimplifiable` could only replace a SILCombine visit implementation.
With the `SWIFT_SILCOMBINE_PASS_WITH_LEGACY` (to be used in Passes.def) it's possible to keep an existing C++ implementation and on top of that add a Swift Simplification pass.

Author: eeckstein

include/swift/SILOptimizer/PassManager/Passes.def

@@ -78,6 +78,10 @@
 #define SWIFT_SILCOMBINE_PASS(Inst)
 #endif
 
+#ifndef SWIFT_SILCOMBINE_PASS_WITH_LEGACY
+#define SWIFT_SILCOMBINE_PASS_WITH_LEGACY(Inst)
+#endif
+
 /// PASS_RANGE(RANGE_ID, START, END)
 ///   Pass IDs between PassKind::START and PassKind::END, inclusive,
 ///   fall within the set known as
@@ -540,5 +544,6 @@ SWIFT_SILCOMBINE_PASS(UncheckedEnumDataInst)
 #undef SWIFT_MODULE_PASS
 #undef SWIFT_FUNCTION_PASS
 #undef SWIFT_SILCOMBINE_PASS
+#undef SWIFT_SILCOMBINE_PASS_WITH_LEGACY
 #undef PASS
 #undef PASS_RANGE

lib/SILOptimizer/SILCombiner/SILCombine.cpp

@@ -610,8 +610,7 @@ void SILCombine_registerInstructionPass(BridgedStringRef instClassName,
   passesRegistered = true;
 }
 
-#define SWIFT_SILCOMBINE_PASS(INST) \
-SILInstruction *SILCombiner::visit##INST(INST *inst) {                     \
+#define _RUN_SWIFT_SIMPLIFICATON(INST) \
   static BridgedInstructionPassRunFn runFunction = nullptr;                \
   static bool passDisabled = false;                                        \
   if (!runFunction) {                                                      \
@@ -633,12 +632,28 @@ SILInstruction *SILCombiner::visit##INST(INST *inst) {                     \
   }                                                                        \
   runSwiftInstructionPass(inst, runFunction);                              \
   return nullptr;                                                          \
+
+#define SWIFT_SILCOMBINE_PASS(INST) \
+SILInstruction *SILCombiner::visit##INST(INST *inst) {                     \
+  _RUN_SWIFT_SIMPLIFICATON(INST)                                           \
+}                                                                          \
+
+#define SWIFT_SILCOMBINE_PASS_WITH_LEGACY(INST) \
+SILInstruction *SILCombiner::visit##INST(INST *inst) {                     \
+  if (auto *result = legacyVisit##INST(inst))                              \
+    return result;                                                         \
+  if (!inst->isDeleted()) {                                                \
+    _RUN_SWIFT_SIMPLIFICATON(INST)                                         \
+  }                                                                        \
+  return nullptr;                                                          \
 }                                                                          \
 
 #define PASS(ID, TAG, DESCRIPTION)
 
 #include "swift/SILOptimizer/PassManager/Passes.def"
 
+#undef _RUN_SWIFT_SIMPLIFICATON
+
 //===----------------------------------------------------------------------===//
 //                                Entry Points
 //===----------------------------------------------------------------------===//

lib/SILOptimizer/SILCombiner/SILCombiner.h

@@ -310,6 +310,9 @@ class SILCombiner :
 #define SWIFT_FUNCTION_PASS(ID, TAG, DESCRIPTION)
 #define SWIFT_SILCOMBINE_PASS(INST) \
   SILInstruction *visit##INST(INST *);
+#define SWIFT_SILCOMBINE_PASS_WITH_LEGACY(INST) \
+  SILInstruction *visit##INST(INST *);          \
+  SILInstruction *legacyVisit##INST(INST *);
 #include "swift/SILOptimizer/PassManager/Passes.def"
 
   /// Instruction visitor helpers.