SIL: a few changes regarding access to a GlobalVariable's static initializer instructions

* add `GlobalVariable.staticInitializerInstructions` to access all initializer instructions of a global
* implement `GlobalVariable.staticInitValue` with `GlobalVariable.staticInitializerInstructions`
* this requires that `InstructionList.reversed()` works without accessing the parent block of the iterator instruction
* allow `Context.erase(instruction:)` to delete instructions from a global's initializer list, which means to handle the case where a deleted instruction has no parent function.

Author: eeckstein

SwiftCompilerSources/Sources/SIL/BasicBlock.swift

@@ -97,7 +97,7 @@ public struct InstructionList : CollectionLikeSequence, IteratorProtocol {
 
   public func reversed() -> ReverseInstructionList {
     if let inst = currentInstruction {
-      let lastInst = inst.parentBlock.bridged.getLastInst().instruction
+      let lastInst = inst.bridged.getLastInstOfParent().instruction
       return ReverseInstructionList(first: lastInst)
     }
     return ReverseInstructionList(first: nil)

SwiftCompilerSources/Sources/SIL/GlobalVariable.swift

@@ -43,8 +43,18 @@ final public class GlobalVariable : CustomStringConvertible, HasShortDescription
     return bridged.isAvailableExternally()
   }
 
+  public var staticInitializerInstructions: InstructionList? {
+    if let firstStaticInitInst = bridged.getFirstStaticInitInst().instruction {
+      return InstructionList(first: firstStaticInitInst)
+    }
+    return nil
+  }
+
   public var staticInitValue: SingleValueInstruction? {
-    bridged.getStaticInitializerValue().instruction as? SingleValueInstruction
+    if let staticInitInsts = staticInitializerInstructions {
+      return staticInitInsts.reversed().first! as? SingleValueInstruction
+    }
+    return nil
   }
 
   /// True if the global's linkage and resilience expansion allow the global

include/swift/SIL/SILBridging.h

@@ -367,7 +367,7 @@ struct BridgedGlobalVar {
   }
 
   SWIFT_IMPORT_UNSAFE
-  inline OptionalBridgedInstruction getStaticInitializerValue() const;
+  inline OptionalBridgedInstruction getFirstStaticInitInst() const;
 
   bool canBeInitializedStatically() const;
 
@@ -467,6 +467,9 @@ struct BridgedInstruction {
   SWIFT_IMPORT_UNSAFE
   inline BridgedBasicBlock getParent() const;
 
+  SWIFT_IMPORT_UNSAFE
+  inline BridgedInstruction getLastInstOfParent() const;
+
   bool isDeleted() const {
     return getInst()->isDeleted();
   }
@@ -1416,11 +1419,12 @@ OptionalBridgedBasicBlock BridgedFunction::getLastBlock() const {
   return {getFunction()->empty() ? nullptr : &*getFunction()->rbegin()};
 }
 
-OptionalBridgedInstruction BridgedGlobalVar::getStaticInitializerValue() const {
-  if (swift::SILInstruction *inst = getGlobal()->getStaticInitializerValue()) {
-    return {inst->asSILNode()};
+OptionalBridgedInstruction BridgedGlobalVar::getFirstStaticInitInst() const {
+  if (getGlobal()->begin() == getGlobal()->end()) {
+    return {nullptr};
   }
-  return {nullptr};
+  swift::SILInstruction *firstInst = &*getGlobal()->begin();
+  return {firstInst->asSILNode()};
 }
 
 BridgedInstruction BridgedMultiValueResult::getParent() const {
@@ -1433,6 +1437,10 @@ BridgedBasicBlock BridgedInstruction::getParent() const {
   return {getInst()->getParent()};
 }
 
+inline BridgedInstruction BridgedInstruction::getLastInstOfParent() const {
+  return {getInst()->getParent()->back().asSILNode()};
+}
+
 BridgedSuccessorArray BridgedInstruction::TermInst_getSuccessors() const {
   auto successors = getAs<swift::TermInst>()->getSuccessors();
   return {{successors.data()}, (SwiftInt)successors.size()};

include/swift/SIL/SILGlobalVariable.h

@@ -42,6 +42,7 @@ class SILGlobalVariable
   static SwiftMetatype registeredMetatype;
 
 public:
+  using iterator = SILBasicBlock::iterator;
   using const_iterator = SILBasicBlock::const_iterator;
 
 private:
@@ -182,6 +183,8 @@ class SILGlobalVariable
 
   const_iterator begin() const { return StaticInitializerBlock.begin(); }
   const_iterator end() const { return StaticInitializerBlock.end(); }
+  iterator begin() { return StaticInitializerBlock.begin(); }
+  iterator end() { return StaticInitializerBlock.end(); }
 
   void dropAllReferences() {
     StaticInitializerBlock.dropAllReferences();

lib/SILOptimizer/SILCombiner/SILCombine.cpp

@@ -617,6 +617,10 @@ void SwiftPassInvocation::eraseInstruction(SILInstruction *inst) {
   if (silCombiner) {
     silCombiner->eraseInstFromFunction(*inst);
   } else {
-    inst->eraseFromParent();
+    if (inst->isStaticInitializerInst()) {
+      inst->getParent()->erase(inst, *getPassManager()->getModule());
+    } else {
+      inst->eraseFromParent();
+    }
   }
 }