[PATCH] D122908: [clang][dataflow] Add support for clang's `__builtin_expect`.

[Yitzhak Mandelbaum via Phabricator via cfe-commits]

ymandel created this revision.
ymandel added reviewers: sgatev, xazax.hun.
Herald added subscribers: tschuett, steakhal, rnkovacs.
Herald added a project: All.
ymandel requested review of this revision.
Herald added a project: clang.

This patch adds basic modeling of `__builtin_expect`, just to propagate the
(first) argument, making the call transparent.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D122908

Files:
  clang/lib/Analysis/FlowSensitive/Transfer.cpp
  clang/unittests/Analysis/FlowSensitive/TransferTest.cpp


Index: clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
===================================================================
--- clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
+++ clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
@@ -2199,6 +2199,32 @@
               });
 }
 
+TEST_F(TransferTest, BuiltinExpect) {
+  std::string Code = R"(
+    void target(long Foo) {
+      long Bar = __builtin_expect(Foo, true);
+      /*[[p]]*/
+    }
+  )";
+  runDataflow(Code,
+              [](llvm::ArrayRef<
+                     std::pair<std::string, DataflowAnalysisState<NoopLattice>>>
+                     Results,
+                 ASTContext &ASTCtx) {
+                ASSERT_THAT(Results, ElementsAre(Pair("p", _)));
+                const auto &Env = Results[0].second.Env;
+
+                const ValueDecl *FooDecl = findValueDecl(ASTCtx, "Foo");
+                ASSERT_THAT(FooDecl, NotNull());
+
+                const ValueDecl *BarDecl = findValueDecl(ASTCtx, "Bar");
+                ASSERT_THAT(BarDecl, NotNull());
+
+                EXPECT_EQ(Env.getValue(*FooDecl, SkipPast::None),
+                          Env.getValue(*BarDecl, SkipPast::None));
+              });
+}
+
 TEST_F(TransferTest, StaticIntSingleVarDecl) {
   std::string Code = R"(
     void target() {
Index: clang/lib/Analysis/FlowSensitive/Transfer.cpp
===================================================================
--- clang/lib/Analysis/FlowSensitive/Transfer.cpp
+++ clang/lib/Analysis/FlowSensitive/Transfer.cpp
@@ -21,6 +21,7 @@
 #include "clang/AST/Stmt.h"
 #include "clang/AST/StmtVisitor.h"
 #include "clang/Analysis/FlowSensitive/DataflowEnvironment.h"
+#include "clang/Basic/Builtins.h"
 #include "clang/Basic/OperatorKinds.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Casting.h"
@@ -426,6 +427,18 @@
         return;
 
       Env.setStorageLocation(*S, *ArgLoc);
+    } else if (S->getDirectCallee() != nullptr &&
+               S->getDirectCallee()->getBuiltinID() ==
+                   Builtin::BI__builtin_expect) {
+      assert(S->getNumArgs() > 0);
+      assert(S->getArg(0) != nullptr);
+      // `__builtin_expect` returns by-value, so strip away any potential
+      // references in the argument.
+      auto *ArgLoc = Env.getStorageLocation(
+          *S->getArg(0)->IgnoreParenImpCasts(), SkipPast::Reference);
+      if (ArgLoc == nullptr)
+        return;
+      Env.setStorageLocation(*S, *ArgLoc);
     }
   }
 


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