Fixes related to handling of empty types (#600)

PR #577 tries to eliminate empty `struct` types by replacing them with a `LegalType::tuple` with zero elements, but this seems to run into problems in some cases, where we end up trying to match up `::none` values with empty `::tuple`s.

An alternative way to handle this is to never create empty `LegalType::tuple`s (and the same for `LegalVal::tuple`), and instead create `LegalType::none` and `LegalVal::none`. PR #577 avoided this because there were various cases in the legalization logic that didn't robustly handle `LegalType::Flavor::none`.

This PR thus includes two main changes:

1. Construct a `::none` type when we have an empty `struct` type.

2. Survery all places that handle the `::tuple` case and extend them to handle the `::none` case if it was missing.

This fixes an issue filed in Falcor's internal GitLab as number 424.

1 files changed, 14 insertions, 0 deletions

diff --git a/source/slang/ir-legalize-types.cpp b/source/slang/ir-legalize-types.cpp
index df3e190e1..9136ad671 100644
--- a/source/slang/ir-legalize-types.cpp
+++ b/source/slang/ir-legalize-types.cpp
@@ -21,6 +21,8 @@ namespace Slang
 
 LegalVal LegalVal::tuple(RefPtr<TuplePseudoVal> tupleVal)
 {
+    SLANG_ASSERT(tupleVal->elements.Count());
+
     LegalVal result;
     result.flavor = LegalVal::Flavor::tuple;
     result.obj = tupleVal;
@@ -343,6 +345,9 @@ static LegalVal legalizeFieldAddress(
 
     switch (legalPtrOperand.flavor)
     {
+    case LegalVal::Flavor::none:
+        return LegalVal();
+
     case LegalVal::Flavor::simple:
         return LegalVal::simple(
             builder->emitFieldAddress(
@@ -457,6 +462,9 @@ static LegalVal legalizeFieldExtract(
 
     switch (legalStructOperand.flavor)
     {
+    case LegalVal::Flavor::none:
+        return LegalVal();
+
     case LegalVal::Flavor::simple:
         return LegalVal::simple(
             builder->emitFieldExtract(
@@ -571,6 +579,9 @@ static LegalVal legalizeGetElementPtr(
 
     switch (legalPtrOperand.flavor)
     {
+    case LegalVal::Flavor::none:
+        return LegalVal();
+
     case LegalVal::Flavor::simple:
         return LegalVal::simple(
             builder->emitElementAddress(
@@ -679,6 +690,9 @@ static LegalVal legalizeMakeStruct(
 
     switch(legalType.flavor)
     {
+    case LegalType::Flavor::none:
+        return LegalVal();
+
     case LegalType::Flavor::simple:
         {
             List<IRInst*> args;