[SILGen] Factor out an emitPointerToPointer helper.

Groundwork for SE-0055: Making pointer nullability explicit.

Author: jrose-apple

lib/SILGen/SILGenConvert.cpp

@@ -374,6 +374,30 @@ SILGenFunction::OpaqueValueRAII::~OpaqueValueRAII() {
   Self.OpaqueValues.erase(entry);
 }
 
+RValue
+SILGenFunction::emitPointerToPointer(SILLocation loc,
+                                     ManagedValue input,
+                                     CanType inputType,
+                                     CanType outputType,
+                                     SGFContext C) {
+  auto converter = getASTContext().getConvertPointerToPointerArgument(nullptr);
+
+  // The generic function currently always requires indirection, but pointers
+  // are always loadable.
+  auto origBuf = emitTemporaryAllocation(loc, input.getType());
+  B.createStore(loc, input.forward(*this), origBuf);
+  auto origValue = emitManagedBufferWithCleanup(origBuf);
+  
+  // Invoke the conversion intrinsic to convert to the destination type.
+  Substitution subs[2] = {
+    getPointerSubstitution(inputType),
+    getPointerSubstitution(outputType),
+  };
+  
+  return emitApplyOfLibraryIntrinsic(loc, converter, subs, origValue, C);
+}
+
+
 namespace {
 
 /// This is an initialization for an address-only existential in memory.

lib/SILGen/SILGenExpr.cpp

@@ -3364,21 +3364,12 @@ RValue RValueEmitter::visitPointerToPointerExpr(PointerToPointerExpr *E,
   // expected level.
   AbstractionPattern origTy(converter->getType()->castTo<AnyFunctionType>()
                                                 ->getInput());
-  auto &origTL = SGF.getTypeLowering(origTy, E->getSubExpr()->getType());
+  CanType inputTy = E->getSubExpr()->getType()->getCanonicalType();
+  auto &origTL = SGF.getTypeLowering(origTy, inputTy);
   ManagedValue orig = SGF.emitRValueAsOrig(E->getSubExpr(), origTy, origTL);
-  // The generic function currently always requires indirection, but pointers
-  // are always loadable.
-  auto origBuf = SGF.emitTemporaryAllocation(E, orig.getType());
-  SGF.B.createStore(E, orig.forward(SGF), origBuf);
-  orig = SGF.emitManagedBufferWithCleanup(origBuf);
-  
-  // Invoke the conversion intrinsic to convert to the destination type.
-  Substitution subs[2] = {
-    SGF.getPointerSubstitution(E->getSubExpr()->getType()),
-    SGF.getPointerSubstitution(E->getType()),
-  };
-  
-  return SGF.emitApplyOfLibraryIntrinsic(E, converter, subs, orig, C);
+
+  CanType outputTy = E->getType()->getCanonicalType();
+  return SGF.emitPointerToPointer(E, orig, inputTy, outputTy, C);
 }
 
 RValue RValueEmitter::visitForeignObjectConversionExpr(

lib/SILGen/SILGenFunction.h

@@ -871,6 +871,14 @@ class LLVM_LIBRARY_VISIBILITY SILGenFunction
                                       SILType loweredResultTy,
                                       const ValueTransform &transform);
 
+  /// Emit a reinterpret-cast from one pointer type to another, using a library
+  /// intrinsic.
+  RValue emitPointerToPointer(SILLocation loc,
+                              ManagedValue input,
+                              CanType inputTy,
+                              CanType outputTy,
+                              SGFContext C);
+
   ManagedValue emitClassMetatypeToObject(SILLocation loc,
                                          ManagedValue v,
                                          SILType resultTy);