[clang][dataflow] Change PruneTriviallyFalseEdges for building CFG

Keeping this false could end up with extra iterations on a lot of loops
that aren't real ones (e.g. they could be a do-while-false for macros),
and makes the analyses very slow.

This patch changes the default for
CFG::BuildOptions.PruneTriviallyFalseEdges to true to avoid it.

Reviewed By: ymandel, xazax.hun, gribozavr2

Differential Revision: https://reviews.llvm.org/D149640

1 files changed, 19 insertions, 1 deletions

diff --git a/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp b/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
index 750d095af451..c8161c8f40fc 100644
--- a/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
+++ b/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
@@ -2644,7 +2644,7 @@ TEST(TransferTest, VarDeclInDoWhile) {
     void target(int *Foo) {
       do {
         int Bar = *Foo;
-      } while (true);
+      } while (false);
       (void)0;
       /*[[p]]*/
     }
@@ -2675,6 +2675,24 @@ TEST(TransferTest, VarDeclInDoWhile) {
       });
 }
 
+TEST(TransferTest, UnreachableAfterWhileTrue) {
+  std::string Code = R"(
+    void target() {
+      while (true) {}
+      (void)0;
+      /*[[p]]*/
+    }
+  )";
+  runDataflow(
+      Code,
+      [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
+         ASTContext &ASTCtx) {
+        // The node after the while-true is pruned because it is trivially
+        // known to be unreachable.
+        ASSERT_TRUE(Results.empty());
+      });
+}
+
 TEST(TransferTest, AggregateInitialization) {
   std::string BracesCode = R"(
     struct A {