Lower CopyLogical before SPIRV control flow legalization. (#8883)

The bug is that the `lowerCopyLogical` pass must run before SPIRV
control flow legalization, because it may generate new loops that needs
to be legalized.

Closes #8838.

Author: csyonghe

source/slang/slang-ir-spirv-legalize.cpp

@@ -2289,6 +2289,19 @@ struct SPIRVLegalizationContext : public SourceEmitterBase
             t->replaceUsesWith(lowered);
         }
 
+        // If older than spirv 1.4, we need more legalization steps due to lack of opcodes.
+        if (!m_sharedContext->isSpirv14OrLater())
+        {
+            // Legalize OpSelect returning non-vector-composites.
+            if (m_codeGenContext->getRequiredLoweringPassSet().nonVectorCompositeSelect)
+                legalizeNonVectorCompositeSelect(m_module);
+
+            // Lower OpCopyLogical to element-wise stores.
+            // Note that it is important to run this pass before processing functions, since we may
+            // introduce new loops that needs to be legalized.
+            lowerCopyLogical(m_module);
+        }
+
         for (auto globalInst : m_module->getGlobalInsts())
         {
             if (auto func = as<IRFunc>(globalInst))
@@ -2333,17 +2346,6 @@ struct SPIRVLegalizationContext : public SourceEmitterBase
         // invalid SPIR-V.
         bool skipFuncParamValidation = false;
         validateAtomicOperations(skipFuncParamValidation, m_sink, m_module->getModuleInst());
-
-        // If older than spirv 1.4, we need more legalization steps due to lack of opcodes.
-        if (!m_sharedContext->isSpirv14OrLater())
-        {
-            // Legalize OpSelect returning non-vector-composites.
-            if (m_codeGenContext->getRequiredLoweringPassSet().nonVectorCompositeSelect)
-                legalizeNonVectorCompositeSelect(m_module);
-
-            // Lower OpCopyLogical to element-wise stores.
-            lowerCopyLogical(m_module);
-        }
     }
 
     void updateFunctionTypes()

tests/spirv/copy-logical-loop.slang

@@ -0,0 +1,39 @@
+//TEST:SIMPLE(filecheck=CHECK): -target spirv -profile spirv_1_3 -g1
+
+// CHECK: OpEntryPoint
+
+public struct PortalView
+{
+    public float3 viewOrigin;
+}
+
+public struct PortalViews
+{
+    public PortalView views[64];
+    public uint viewBits;
+    public Optional<PortalView> PortalForStencil(uint stencil)
+    {
+        // -g1 causes `this` to be preloaded into a local variable for
+        // debugging.
+        // when emitting code for spirv_1_3 where there is no OpCopyLogical,
+        // we have to generate a loop to copy the `views` array from the constant buffer
+        // into the local variable for debugging.
+        // The loop must be generated before control flow legalization for SPIRV
+        // otherwise we will generate invalid SPIRV.
+        if ((viewBits & stencil) == 0)
+            return none;
+        return views[firstbithigh(stencil)];
+    }
+};
+
+ConstantBuffer<PortalViews> CPortals;
+RWStructuredBuffer<float4> outputBuffer;
+
+[numthreads(1,1,1)]
+void main()
+{
+    if (let portal = CPortals.PortalForStencil(0xff))
+    {
+        outputBuffer[0] = portal.viewOrigin.x;
+    }
+}