Clone name hint decoration when emiting Undefined (#6415)

* Clone name hint decoration when emiting Undefined

When emiting "Undefined", we lost the information of where it was
synthasized from. This prevents us from providing more helpful error
messages.

The issue was the when we handle "IRLoop", the inputs parameters to the
Phi didn't clone the name hint decoration. This commit clones them when
emiting "Undefined".

* Adding more test case

---------

Co-authored-by: Yong He <[email protected]>

Author: jkwak-work

source/slang/slang-ir-ssa.cpp

@@ -694,6 +694,7 @@ IRInst* readVarRec(ConstructSSAContext* context, SSABlockInfo* blockInfo, IRVar*
 
             auto type = var->getDataType()->getValueType();
             val = blockInfo->builder.emitUndefined(type);
+            cloneRelevantDecorations(var, val);
         }
         else if (!multiplePreds)
         {
@@ -776,6 +777,7 @@ IRInst* readVar(ConstructSSAContext* context, SSABlockInfo* blockInfo, IRVar* va
         //
         auto type = var->getDataType()->getValueType();
         val = blockInfo->builder.emitUndefined(type);
+        cloneRelevantDecorations(var, val);
         writeVar(context, blockInfo, var, val);
         return val;
     }

tests/diagnostics/uninitialized-variable-name-in-error-message.slang

@@ -0,0 +1,37 @@
+//TEST:SIMPLE(filecheck=CHK):
+
+// Test if the variable name is a part of the error message
+// when it is used inside of for-loop
+
+RWStructuredBuffer<float> gInput;
+RWStructuredBuffer<float> outputBuffer;
+
+//CHK-DAG: ([[#@LINE+1]]): warning 41016: use of uninitialized variable 'a'
+float func1() { float a; return a; }
+
+//CHK-DAG: ([[#@LINE+1]]): warning 41016: use of uninitialized variable 'b'
+float func2() { float b; return b; }
+
+int test(int inVal)
+{
+    return inVal;
+}
+
+[Shader("compute")]
+[NumThreads(4, 1, 1)]
+void computeMain(int3 dispatchThreadID : SV_DispatchThreadID)
+{
+    int tid = dispatchThreadID.x;
+    int inVal1; // intentionally uninitialized
+    int inVal2; // intentionally uninitialized
+
+    for (int i = 0; i <2; ++i)
+    {
+        // CHK-DAG: ([[#@LINE+1]]): warning 41016: use of uninitialized variable 'inVal1'
+        int outVal = test(inVal1);
+
+        // CHK-DAG: ([[#@LINE+1]]): warning 41016: use of uninitialized variable 'inVal2'
+        outVal += test(inVal2);
+        outputBuffer[tid] = outVal;
+    }
+}