Count lowered parameters for a formal parameter using just the

AbstractionPattern.

The old logic was wrong for vanishing tuples: a non-tuple substituted
type might correspond to multiple lowered parameters if it's the result
of substituting into a vanishing tuple that also contains empty pack
expansions.

Test to follow later in this PR.

Author: rjmccall

lib/SILGen/SILGenApply.cpp

@@ -2191,43 +2191,35 @@ ManagedValue SILGenFunction::emitStringLiteral(SILLocation loc,
 
 /// Count the number of SILParameterInfos that are needed in order to
 /// pass the given argument.
-static unsigned getFlattenedValueCount(AbstractionPattern origType,
-                                       CanType substType) {
-  // The count is always 1 unless the substituted type is a tuple.
-  auto substTuple = dyn_cast<TupleType>(substType);
-  if (!substTuple)
-    return 1;
-
-  // If the original type is opaque, the count is 1 anyway.
-  if (origType.isTypeParameter())
+static unsigned getFlattenedValueCount(AbstractionPattern origType) {
+  // The count is always 1 unless the original type is a tuple.
+  if (!origType.isTuple())
     return 1;
 
-  // Otherwise, add up the elements.
+  // Add up the elements.
   unsigned count = 0;
-  origType.forEachTupleElement(substTuple, [&](TupleElementGenerator &elt) {
-    // Expansion components turn into a single parameter.
-    if (elt.isOrigPackExpansion()) {
+  for (auto elt : origType.getTupleElementTypes()) {
+    // Expansion components turn into a single pack parameter.
+    if (elt.isPackExpansion()) {
       count++;
 
     // Recursively expand scalar components.
     } else {
-      count += getFlattenedValueCount(elt.getOrigType(),
-                                      elt.getSubstTypes()[0]);
+      count += getFlattenedValueCount(elt);
     }
-  });
+  }
   return count;
 }
 
 /// Count the number of SILParameterInfos that are needed in order to
 /// pass the given argument.
 static unsigned getFlattenedValueCount(AbstractionPattern origType,
-                                       CanType substType,
                                        ImportAsMemberStatus foreignSelf) {
   // C functions imported as static methods don't consume any real arguments.
   if (foreignSelf.isStatic())
     return 0;
 
-  return getFlattenedValueCount(origType, substType);
+  return getFlattenedValueCount(origType);
 }
 
 namespace {
@@ -3195,7 +3187,6 @@ class ArgEmitter {
       auto defArg = std::move(arg).asKnownDefaultArg();
 
       auto numParams = getFlattenedValueCount(origParamType,
-                                              substParamType,
                                               ImportAsMemberStatus());
       DelayedArguments.emplace_back(defArg,
                                     defArg->getDefaultArgsOwner(),
@@ -3576,7 +3567,7 @@ class ArgEmitter {
 
   void emitExpandedBorrowed(Expr *arg, AbstractionPattern origParamType) {
     CanType substArgType = arg->getType()->getCanonicalType();
-    auto count = getFlattenedValueCount(origParamType, substArgType);
+    auto count = getFlattenedValueCount(origParamType);
     auto claimedParams = claimNextParameters(count);
 
     SILType loweredSubstArgType = SGF.getLoweredType(substArgType);
@@ -3626,7 +3617,7 @@ class ArgEmitter {
 
   void emitExpandedConsumed(Expr *arg, AbstractionPattern origParamType) {
     CanType substArgType = arg->getType()->getCanonicalType();
-    auto count = getFlattenedValueCount(origParamType, substArgType);
+    auto count = getFlattenedValueCount(origParamType);
     auto claimedParams = claimNextParameters(count);
 
     SILType loweredSubstArgType = SGF.getLoweredType(substArgType);
@@ -4432,10 +4423,8 @@ struct ParamLowering {
           if (substParam.isInOut()) {
             count += 1;
           } else {
-            count += getFlattenedValueCount(
-                origParamType,
-                substParam.getParameterType()->getCanonicalType(),
-                ImportAsMemberStatus());
+            count += getFlattenedValueCount(origParamType,
+                                            ImportAsMemberStatus());
           }
         }
       }