From 2226ae0bbbf2cbd5ea2da8aaaa04c9c466af56c3 Mon Sep 17 00:00:00 2001
From: winmad <winmad.wlf@gmail.com>
Date: Fri, 14 Apr 2023 11:36:19 -0700
Subject: Bugfix: compiler will run forever to eliminate dead code (#2809)

* Add a test case that the compile will run forever

* Fix.

* fix.

---------

Co-authored-by: Lifan Wu <lifanw@nvidia.com>
Co-authored-by: Yong He <yhe@nvidia.com>
---
 source/slang/slang-ir.cpp                          |  2 ++
 tests/autodiff/for-loop-eliminate-dead-code.slang  | 41 ++++++++++++++++++++++
 ...for-loop-eliminate-dead-code.slang.expected.txt |  4 +++
 tools/gfx/d3d12/d3d12-device.cpp                   |  2 +-
 4 files changed, 48 insertions(+), 1 deletion(-)
 create mode 100644 tests/autodiff/for-loop-eliminate-dead-code.slang
 create mode 100644 tests/autodiff/for-loop-eliminate-dead-code.slang.expected.txt

diff --git a/source/slang/slang-ir.cpp b/source/slang/slang-ir.cpp
index 92da981ad..dd3034da1 100644
--- a/source/slang/slang-ir.cpp
+++ b/source/slang/slang-ir.cpp
@@ -6889,6 +6889,8 @@ namespace Slang
         SLANG_ASSERT(other);
         if (other->getPrevInst() == this)
             return;
+        if (other == this)
+            return;
         _insertAt(other->getPrevInst(), other, other->getParent());
     }
 
diff --git a/tests/autodiff/for-loop-eliminate-dead-code.slang b/tests/autodiff/for-loop-eliminate-dead-code.slang
new file mode 100644
index 000000000..be1093c23
--- /dev/null
+++ b/tests/autodiff/for-loop-eliminate-dead-code.slang
@@ -0,0 +1,41 @@
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX:-vk -compute -shaderobj -output-using-type
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -shaderobj -output-using-type
+
+//TEST_INPUT:ubuffer(data=[0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+static const uint kMaxSurfaceBounces = 2;
+
+[BackwardDifferentiable]
+void updatePathContrib(inout float3 result, float3 val)
+{
+    result = result + val;
+}
+
+[BackwardDifferentiable]
+float3 evalPath(uint2 pixel)
+{
+    float3 result = float3(0.f);
+    float3 thp = float3(1.f);
+
+    [MaxIters(kMaxSurfaceBounces)]
+    for (int i = 0; i < kMaxSurfaceBounces; i++)
+    {
+        float3 neeContrib = float3(1.f);
+        updatePathContrib(result, thp * neeContrib);
+        thp = thp * float3(0.9f);
+    }
+    return result;
+}
+
+void execute(const uint2 pixel)
+{
+    float3 dColor = float3(1.f);
+    __bwd_diff(evalPath)(pixel, dColor);
+}
+
+[numthreads(64, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    execute(dispatchThreadID.xy);
+}
diff --git a/tests/autodiff/for-loop-eliminate-dead-code.slang.expected.txt b/tests/autodiff/for-loop-eliminate-dead-code.slang.expected.txt
new file mode 100644
index 000000000..4465d8c34
--- /dev/null
+++ b/tests/autodiff/for-loop-eliminate-dead-code.slang.expected.txt
@@ -0,0 +1,4 @@
+type: float
+0.000000
+0.000000
+0.000000
\ No newline at end of file
diff --git a/tools/gfx/d3d12/d3d12-device.cpp b/tools/gfx/d3d12/d3d12-device.cpp
index 9bf54a01b..ad71388c4 100644
--- a/tools/gfx/d3d12/d3d12-device.cpp
+++ b/tools/gfx/d3d12/d3d12-device.cpp
@@ -407,7 +407,7 @@ Result DeviceImpl::initialize(const Desc& desc)
 
     SharedLibrary::Handle d3dModule;
 #if SLANG_WINDOWS_FAMILY
-    const char* libName = "d3d11";
+    const char* libName = "d3d12";
 #else
     const char* libName = "vkd3d-proton-d3d12";
 #endif
-- 
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