From 5c9f011fa4948d1f70689b03ddcd203cb2525b2b Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Fri, 20 Dec 2024 00:53:24 -0800
Subject: Fix crash during loop unrolling. (#5920)

---
 source/slang/slang-ir-loop-unroll.cpp |  3 +++
 tests/ir/loop-unroll-3.slang          | 38 +++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)
 create mode 100644 tests/ir/loop-unroll-3.slang

diff --git a/source/slang/slang-ir-loop-unroll.cpp b/source/slang/slang-ir-loop-unroll.cpp
index 5f9c53bc7..6b001a562 100644
--- a/source/slang/slang-ir-loop-unroll.cpp
+++ b/source/slang/slang-ir-loop-unroll.cpp
@@ -463,6 +463,9 @@ bool unrollLoopsInFunc(
 
     for (auto loop : loops)
     {
+        if (!loop->parent)
+            continue;
+
         // Remove any continue jumps from the loop.
         eliminateContinueBlocks(module, loop);
 
diff --git a/tests/ir/loop-unroll-3.slang b/tests/ir/loop-unroll-3.slang
new file mode 100644
index 000000000..4e5275e67
--- /dev/null
+++ b/tests/ir/loop-unroll-3.slang
@@ -0,0 +1,38 @@
+//TEST:COMPARE_COMPUTE(filecheck-buffer=CHECK): -output-using-type
+
+//TEST_INPUT:set buffer = ubuffer(data=[0 0 0 0], stride=4)
+RWStructuredBuffer<float> buffer;
+
+struct Foo<let D : int>
+{
+    float load()
+    {
+        int idx[D];
+        [ForceUnroll]
+        for (int i = 0; i < D; ++i)
+            idx[i] = 0;
+        [ForceUnroll]
+        for (int i = 0; i < D-2; ++i)
+            idx[i] = 0;
+        float result = 100.0;
+        [ForceUnroll]
+        for (int i = 0; i < 1; i++)
+            result += buffer[idx[0]];
+
+        return result;
+    }
+}
+
+//TEST_INPUT:set result = out ubuffer(data=[0 0 0 0], stride=4)
+uniform RWStructuredBuffer<float> result;
+
+[shader("compute")]
+void computeMain(uint3 dispatchThreadID: SV_DispatchThreadID)
+{
+    Foo<2> biases = {};
+
+    // Test that we can unroll loops of 0 iterations.
+    result[0] = biases.load();
+
+    // CHECK: 100.0
+}
\ No newline at end of file
-- 
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