From ace9a8dc7e4353b1cf8e846abe2b8dc53ecdbc59 Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Fri, 25 May 2018 10:01:34 -0400
Subject: Fixes 574. Eliminate empty structs during type legalization (#577)

---
 source/slang/ir-legalize-types.cpp            |  2 ++
 source/slang/legalize-types.cpp               |  6 ++++++
 tests/compute/empty-struct.slang              | 19 +++++++++++++++++++
 tests/compute/empty-struct.slang.expected.txt |  4 ++++
 4 files changed, 31 insertions(+)
 create mode 100644 tests/compute/empty-struct.slang
 create mode 100644 tests/compute/empty-struct.slang.expected.txt

diff --git a/source/slang/ir-legalize-types.cpp b/source/slang/ir-legalize-types.cpp
index 86907dfde..df3e190e1 100644
--- a/source/slang/ir-legalize-types.cpp
+++ b/source/slang/ir-legalize-types.cpp
@@ -818,6 +818,8 @@ static LegalVal legalizeInst(
             args,
             inst->getOperandCount());
 
+    case kIROp_undefined:
+        return LegalVal();
     default:
         // TODO: produce a user-visible diagnostic here
         SLANG_UNEXPECTED("non-simple operand(s)!");
diff --git a/source/slang/legalize-types.cpp b/source/slang/legalize-types.cpp
index bbfa6264d..6ab597d93 100644
--- a/source/slang/legalize-types.cpp
+++ b/source/slang/legalize-types.cpp
@@ -301,6 +301,12 @@ struct TupleTypeBuilder
 
     LegalType getResult()
     {
+        // If this is an empty struct, return a none type
+        // This helps get rid of emtpy structs that often trips up the 
+        // downstream compiler
+        if (!anyOrdinary && !anySpecial && !anyComplex)
+            return LegalType::tuple(new TuplePseudoType());
+
         // If we didn't see anything "special"
         // then we can use the type as-is.
         // we can conceivably just use the type as-is
diff --git a/tests/compute/empty-struct.slang b/tests/compute/empty-struct.slang
new file mode 100644
index 000000000..51094fad5
--- /dev/null
+++ b/tests/compute/empty-struct.slang
@@ -0,0 +1,19 @@
+//TEST(smoke,compute):COMPARE_COMPUTE:
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):dxbinding(0),glbinding(0),out
+// Confirm that generics syntax can be used in user
+// code and generates valid output.
+
+RWStructuredBuffer<float> outputBuffer;
+
+struct Simple
+{
+    float getVal() {return 1.0;}
+};
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    Simple s;
+	float outVal = s.getVal();
+	outputBuffer[dispatchThreadID.x] = outVal;
+}
\ No newline at end of file
diff --git a/tests/compute/empty-struct.slang.expected.txt b/tests/compute/empty-struct.slang.expected.txt
new file mode 100644
index 000000000..e143b7f20
--- /dev/null
+++ b/tests/compute/empty-struct.slang.expected.txt
@@ -0,0 +1,4 @@
+3F800000
+3F800000
+3F800000
+3F800000
\ No newline at end of file
-- 
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