Fix DCE on mutable calls in a loop. (#2943)

* Fix DCE on mutable calls in a loop.

* More accurate in-loop test.

* code review  fixes.

* Fix.

---------

Co-authored-by: Yong He <yhe@nvidia.com>

2 files changed, 41 insertions, 0 deletions

diff --git a/tests/bugs/mutating/mutating-call-in-loop-dce.slang b/tests/bugs/mutating/mutating-call-in-loop-dce.slang
new file mode 100644
index 000000000..372cb61b0
--- /dev/null
+++ b/tests/bugs/mutating/mutating-call-in-loop-dce.slang
@@ -0,0 +1,39 @@
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -shaderobj -output-using-type
+
+// Confirm that a SideEffectFree mutable method does not get DCE'd when
+// it is called from within a loop.
+
+struct C
+{
+    int a;
+    [mutating]
+    int add()
+    {
+        a++;
+        return a;
+    }
+    [mutating]
+    void init()
+    {
+        a = 0;
+    }
+}
+int doSomething(C d)
+{
+    int rs = 0;
+    for (int i = 0; i < 10; i++)
+        rs = d.add();
+    return rs;
+}
+
+//TEST_INPUT:ubuffer(data=[0], stride=4):out, name outputBuffer
+RWStructuredBuffer<int> outputBuffer;
+
+[numthreads(1, 1, 1)]
+void computeMain(int3 dispatchThreadID : SV_DispatchThreadID)
+{
+    int tid = dispatchThreadID.x;
+    C c;
+    c.init();
+    outputBuffer[tid] = doSomething(c);
+}
\ No newline at end of file
diff --git a/tests/bugs/mutating/mutating-call-in-loop-dce.slang.expected.txt b/tests/bugs/mutating/mutating-call-in-loop-dce.slang.expected.txt
new file mode 100644
index 000000000..2c29f3f9e
--- /dev/null
+++ b/tests/bugs/mutating/mutating-call-in-loop-dce.slang.expected.txt
@@ -0,0 +1,2 @@
+type: int32_t
+10