Fix collectDataFromPredecessors to collect data from the passed branch (

vgvassilev#1051)

Before the fix, we didn't collect data from varsData at all, and it wasn't merge afterward either. Now, we start collecting data from varsData, ensuring the final data of the CFG block is correct.

Fixes:vgvassilev#855

lib/Differentiator/TBRAnalyzer.cpp

@@ -484,7 +484,7 @@ TBRAnalyzer::collectDataFromPredecessors(VarsData* varsData,
   std::unordered_map<const clang::VarDecl*, VarData*> result;
   if (varsData != limit) {
     // Copy data from every predecessor.
-    for (auto* pred = varsData->m_Prev; pred != limit; pred = pred->m_Prev) {
+    for (auto* pred = varsData; pred != limit; pred = pred->m_Prev) {
       // If a variable from 'pred' is not present in 'result', place it there.
       for (auto& pair : *pred)
         if (result.find(pair.first) == result.end())

test/Analyses/TBR.cpp

@@ -11,6 +11,16 @@ double f1(double x) {
   return t;
 } // == x^3
 
+double f2(double val) {
+  double res = 0;
+  for (int i=1; i<5; ++i) {
+    if (i == 3)
+      continue;
+    res += i * val;
+  }
+  return res;
+}
+
 #define TEST(F, x) { \
   result[0] = 0; \
   auto F##grad = clad::gradient<clad::opts::enable_tbr>(F);\
@@ -21,5 +31,5 @@ double f1(double x) {
 int main() {
   double result[3] = {};
   TEST(f1, 3); // CHECK-EXEC: {27.00}
-
+  TEST(f2, 3); // CHECK-EXEC: {9.00}
 }