Fix successor computation for `switch` instruction (#520)

Fixes #519

The code was leaving out the `default` label from the successor list,
which would break any passes that require an accurate CFG (with the big
one right now being the SSA-formation pass).

2 files changed, 46 insertions, 0 deletions

diff --git a/tests/bugs/gh-519.slang b/tests/bugs/gh-519.slang
new file mode 100644
index 000000000..35bf6dcd7
--- /dev/null
+++ b/tests/bugs/gh-519.slang
@@ -0,0 +1,42 @@
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -dx12
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX:-vk -compute
+
+// This bug involved incorrect computation of the successor
+// blocks for a `switch`, which led to incorrect SSA form.
+
+int test(int val)
+{
+    int tmp = 0;
+    switch(val)
+    {
+    case 0:
+        tmp = 1;
+        break;
+
+    case 1:
+        tmp = 2;
+        break;
+
+    case 2:
+        tmp = 3;
+        break;
+
+    default:
+        tmp = val + 1;
+        break;
+    }
+    return tmp;
+}
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):dxbinding(0),glbinding(0),out
+RWStructuredBuffer<int> gBuffer;
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    uint tid = dispatchThreadID.x;
+    int val = int(tid);
+    val = test(val);
+    gBuffer[tid] = val;
+}
\ No newline at end of file
diff --git a/tests/bugs/gh-519.slang.expected.txt b/tests/bugs/gh-519.slang.expected.txt
new file mode 100644
index 000000000..94ebaf900
--- /dev/null
+++ b/tests/bugs/gh-519.slang.expected.txt
@@ -0,0 +1,4 @@
+1
+2
+3
+4