[PATCH] D111568: [clang] Omit most AttributedStatements from the CFG

[Nico Weber via Phabricator via cfe-commits]

thakis updated this revision to Diff 378996.
thakis added a comment.

rename param; assert isa<NullStmt>


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D111568/new/

https://reviews.llvm.org/D111568

Files:
  clang/lib/Analysis/CFG.cpp
  clang/test/SemaCXX/switch-implicit-fallthrough.cpp
  clang/test/SemaCXX/unreachable-code.cpp


Index: clang/test/SemaCXX/unreachable-code.cpp
===================================================================
--- clang/test/SemaCXX/unreachable-code.cpp
+++ clang/test/SemaCXX/unreachable-code.cpp
@@ -77,3 +77,25 @@
     return;
   bar(); // no-warning
 }
+
+namespace pr52103 {
+
+void g(int a);
+
+void f(int a) {
+  if (a > 4) [[ likely ]] { // no-warning
+    return;
+  }
+
+  if (a > 4) [[ unlikely ]] { // no-warning
+    return;
+
+    return; // expected-warning {{will never be executed}}
+  }
+
+  [[clang::musttail]] return g(a); // no-warning
+
+  [[clang::musttail]] return g(a); // expected-warning {{will never be executed}}
+}
+
+}
Index: clang/test/SemaCXX/switch-implicit-fallthrough.cpp
===================================================================
--- clang/test/SemaCXX/switch-implicit-fallthrough.cpp
+++ clang/test/SemaCXX/switch-implicit-fallthrough.cpp
@@ -50,6 +50,8 @@
       break;
   }
   switch (n / 20) {
+    [[likely]] case 6:
+      [[clang::fallthrough]];
     case 7:
       n += 400;
       [[clang::fallthrough]];
@@ -73,6 +75,8 @@
       n += 800;
   }
   switch (n / 30) {
+    case 6:
+      [[unlikely, clang::fallthrough]];
     case 11:
     case 12:  // no warning here, intended fall-through, no statement between labels
       n += 1600;
Index: clang/lib/Analysis/CFG.cpp
===================================================================
--- clang/lib/Analysis/CFG.cpp
+++ clang/lib/Analysis/CFG.cpp
@@ -542,6 +542,7 @@
   // Visitors to walk an AST and construct the CFG.
   CFGBlock *VisitInitListExpr(InitListExpr *ILE, AddStmtChoice asc);
   CFGBlock *VisitAddrLabelExpr(AddrLabelExpr *A, AddStmtChoice asc);
+  CFGBlock *VisitAttributedStmt(AttributedStmt *A, AddStmtChoice asc);
   CFGBlock *VisitBinaryOperator(BinaryOperator *B, AddStmtChoice asc);
   CFGBlock *VisitBreakStmt(BreakStmt *B);
   CFGBlock *VisitCallExpr(CallExpr *C, AddStmtChoice asc);
@@ -2149,6 +2150,9 @@
     case Stmt::InitListExprClass:
       return VisitInitListExpr(cast<InitListExpr>(S), asc);
 
+    case Stmt::AttributedStmtClass:
+      return VisitAttributedStmt(cast<AttributedStmt>(S), asc);
+
     case Stmt::AddrLabelExprClass:
       return VisitAddrLabelExpr(cast<AddrLabelExpr>(S), asc);
 
@@ -2398,8 +2402,32 @@
   return Block;
 }
 
-CFGBlock *CFGBuilder::VisitUnaryOperator(UnaryOperator *U,
-           AddStmtChoice asc) {
+static bool isFallthroughStatement(const AttributedStmt *A) {
+  bool isFallthrough = hasSpecificAttr<FallThroughAttr>(A->getAttrs());
+  assert((!isFallthrough || isa<NullStmt>(A->getSubStmt())) &&
+         "expected fallthrough not to have children");
+  return isFallthrough;
+}
+
+CFGBlock *CFGBuilder::VisitAttributedStmt(AttributedStmt *A,
+                                          AddStmtChoice asc) {
+  // AttributedStmts for [[likely]] can have arbitrary statements as children,
+  // and the current visitation order here would add the AttributedStmts
+  // for [[likely]] after the child nodes, which is undesirable: For example,
+  // if the child contains an unconditional return, the [[likely]] would be
+  // considered unreachable.
+  // So only add the AttributedStmt for FallThrough, which has CFG effects and
+  // also no children, and omit the others. None of the other current StmtAttrs
+  // have semantic meaning for the CFG.
+  if (isFallthroughStatement(A) && asc.alwaysAdd(*this, A)) {
+    autoCreateBlock();
+    appendStmt(Block, A);
+  }
+
+  return VisitChildren(A);
+}
+
+CFGBlock *CFGBuilder::VisitUnaryOperator(UnaryOperator *U, AddStmtChoice asc) {
   if (asc.alwaysAdd(*this, U)) {
     autoCreateBlock();
     appendStmt(Block, U);

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