Handling of switch with empty body (shader-slang#1284)

* Added handling for empty switch body.
Added test for empty switch.

* Fix testing for case in switch.

Author: jsmall-zzz

source/slang/slang-lower-to-ir.cpp

@@ -3592,6 +3592,41 @@ struct StmtLoweringVisitor : StmtVisitor<StmtLoweringVisitor>
         return newCaseLabel;
     }
 
+    bool hasSwitchCases(Stmt* inStmt)
+    {
+        Stmt* stmt = inStmt;
+        // Unwrap any surrounding `{ ... }` so we can look
+        // at the statement inside.
+        while (auto blockStmt = as<BlockStmt>(stmt))
+        {
+            stmt = blockStmt->body;
+            continue;
+        }
+
+        if (auto seqStmt = as<SeqStmt>(stmt))
+        {
+            // Walk through the children looking for cases
+            for (auto childStmt : seqStmt->stmts)
+            {
+                if (hasSwitchCases(childStmt))
+                {
+                    return true;
+                }
+            }
+        }
+        else if (auto caseStmt = as<CaseStmt>(stmt))
+        {
+            return true;
+        }
+        else if (auto defaultStmt = as<DefaultStmt>(stmt))
+        {
+            // A 'default:' is a kind of case. 
+            return true;
+        }
+
+        return false;
+    }
+
     // Given a statement that appears as (or in) the body
     // of a `switch` statement
     void lowerSwitchCases(Stmt* inStmt, SwitchStmtInfo* info)
@@ -3734,6 +3769,14 @@ struct StmtLoweringVisitor : StmtVisitor<StmtLoweringVisitor>
         // First emit code to compute the condition:
         auto conditionVal = getSimpleVal(context, lowerRValueExpr(context, stmt->condition));
 
+        // Check for any cases or default. 
+        if (!hasSwitchCases(stmt->body))
+        {
+            // If we don't have any case/default then nothing inside switch can be executed (other than condition)
+            // so we are done.
+            return;
+        }
+
         // Remember the initial block so that we can add to it
         // after we've collected all the `case`s
         auto initialBlock = builder->getBlock();

tests/bugs/empty-switch.slang

@@ -0,0 +1,29 @@
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute
+//TEST(compute,vulkan):COMPARE_COMPUTE_EX:-vk -slang -compute
+//TEST(compute):COMPARE_COMPUTE_EX:-cpu -slang -compute
+//TEST(compute):COMPARE_COMPUTE_EX:-cuda -slang -compute
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):out, name outputBuffer
+RWStructuredBuffer<int> outputBuffer;
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    int index = int(dispatchThreadID.x);   
+    
+    int a = index;
+    
+    // This is kind of silly - but it is a valid construct.
+    // We want to check condition expression is executed though
+    switch (++a)
+    {
+    }
+
+    switch (index)
+    {
+        // This should not be executed
+        a += 10;
+    }
+
+    outputBuffer[index] = a;
+}

tests/bugs/empty-switch.slang.expected.txt

@@ -0,0 +1,4 @@
+1
+2
+3
+4