Fix reconvergence test to be agnostic to wave size

Author: luciechoi

test/Feature/MaximalReconvergence/subgroup_uniform_control_flow.test

@@ -3,20 +3,26 @@ RWStructuredBuffer<uint> Out : register(u0);
 
 [numthreads(8,1,1)]
 void main(uint3 TID : SV_GroupThreadID) {
+    // Use `WaveActiveSum()` to count wave size, since
+    // `WaveGetLaneCount` is not implemented yet in clang compiler.
+    float maxActiveLaneCount = min(WaveActiveSum(1), 8);
+    float result = 0;
+
     // First non-uniform branch
-    if (TID.x < 4) {
+    if (TID.x % 2 == 0) {
         // Second non-uniform branch
-        if (TID.x % 2 == 0) {
-            Out[TID.x] = WaveActiveSum(TID.x);
+        if (TID.x % 4 == 0) {
+            result += WaveActiveSum(4.0/maxActiveLaneCount);
         } else {
-            Out[TID.x] = WaveActiveMax(TID.x);
+            result += WaveActiveSum(8.0/maxActiveLaneCount);
         }
         // Must reconverge here with maximal reconvergence
-        Out[TID.x] += WaveActiveMax(TID.x);
-    } else {
-        Out[4] = WaveActiveMax(TID.x);
+        result += WaveActiveSum(2.0/maxActiveLaneCount);
     }
-    Out[TID.x] += WaveActiveMax(TID.x);
+
+    // Must reconverge here with maximal reconvergence
+    result += WaveActiveSum(1.0/maxActiveLaneCount);
+    Out[TID.x] = uint(result);
 }
 
 //--- pipeline.yaml
@@ -56,4 +62,4 @@ DescriptorSets:
 
 # CHECK: Name: Out
 # CHECK: Format: UInt32
-# CHECK: Data: [ 12, 13, 12, 13, 14, 7, 7, 7 ]
+# CHECK: Data: [ 3, 1, 4, 1, 3, 1, 4, 1 ]