From: Ted Kremenek <kremenek@apple.com>
Date: Tue, 13 Nov 2012 00:12:13 +0000 (+0000)
Subject: Fix bad CFG construction bug when handling C++ 'try' statements.
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=8f81acfa95a5d2a22fc875c1a10901eaa30b8405;p=clang

Fix bad CFG construction bug when handling C++ 'try' statements.

This code assigned the last created CFGBlock* to the variable 'Block',
which is a scratch variable which is null'ed out after a block is
completed.  By assigning the last created block to 'Block', we start
editing a completed block, inserting CFGStmts that should be in
another block.  This was the case with 'try'.  The test case that
showed this had a while loop inside a 'try', and the logic before
the while loop was being included as part of the "condition block"
for the loop.  This showed up as a bogus dead store, but could
have lots of implications.

Turns out this bug was replicated a few times within CFG.cpp, so
I went and fixed up those as well.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@167788 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Analysis/CFG.cpp b/lib/Analysis/CFG.cpp
index 94c005f552..315e54380b 100644
--- a/lib/Analysis/CFG.cpp
+++ b/lib/Analysis/CFG.cpp
@@ -1648,8 +1648,10 @@ CFGBlock *CFGBuilder::VisitDeclSubExpr(DeclStmt *DS) {
 
   // If the type of VD is a VLA, then we must process its size expressions.
   for (const VariableArrayType* VA = FindVA(VD->getType().getTypePtr());
-       VA != 0; VA = FindVA(VA->getElementType().getTypePtr()))
-    Block = addStmt(VA->getSizeExpr());
+       VA != 0; VA = FindVA(VA->getElementType().getTypePtr())) {
+    if (CFGBlock *newBlock = addStmt(VA->getSizeExpr()))
+      LastBlock = newBlock;
+  }
 
   // Remove variable from local scope.
   if (ScopePos && VD == *ScopePos)
@@ -1767,7 +1769,7 @@ CFGBlock *CFGBuilder::VisitIfStmt(IfStmt *I) {
   // Add the condition as the last statement in the new block.  This may create
   // new blocks as the condition may contain control-flow.  Any newly created
   // blocks will be pointed to be "Block".
-  Block = addStmt(I->getCond());
+  CFGBlock *LastBlock = addStmt(I->getCond());
 
   // Finally, if the IfStmt contains a condition variable, add both the IfStmt
   // and the condition variable initialization to the CFG.
@@ -1775,11 +1777,11 @@ CFGBlock *CFGBuilder::VisitIfStmt(IfStmt *I) {
     if (Expr *Init = VD->getInit()) {
       autoCreateBlock();
       appendStmt(Block, I->getConditionVariableDeclStmt());
-      addStmt(Init);
+      LastBlock = addStmt(Init);
     }
   }
 
-  return Block;
+  return LastBlock;
 }
 
 
@@ -2611,7 +2613,7 @@ CFGBlock *CFGBuilder::VisitSwitchStmt(SwitchStmt *Terminator) {
   // Add the terminator and condition in the switch block.
   SwitchTerminatedBlock->setTerminator(Terminator);
   Block = SwitchTerminatedBlock;
-  Block = addStmt(Terminator->getCond());
+  CFGBlock *LastBlock = addStmt(Terminator->getCond());
 
   // Finally, if the SwitchStmt contains a condition variable, add both the
   // SwitchStmt and the condition variable initialization to the CFG.
@@ -2619,11 +2621,11 @@ CFGBlock *CFGBuilder::VisitSwitchStmt(SwitchStmt *Terminator) {
     if (Expr *Init = VD->getInit()) {
       autoCreateBlock();
       appendStmt(Block, Terminator->getConditionVariableDeclStmt());
-      addStmt(Init);
+      LastBlock = addStmt(Init);
     }
   }
 
-  return Block;
+  return LastBlock;
 }
   
 static bool shouldAddCase(bool &switchExclusivelyCovered,
@@ -2807,8 +2809,7 @@ CFGBlock *CFGBuilder::VisitCXXTryStmt(CXXTryStmt *Terminator) {
 
   assert(Terminator->getTryBlock() && "try must contain a non-NULL body");
   Block = NULL;
-  Block = addStmt(Terminator->getTryBlock());
-  return Block;
+  return addStmt(Terminator->getTryBlock());
 }
 
 CFGBlock *CFGBuilder::VisitCXXCatchStmt(CXXCatchStmt *CS) {
@@ -2949,15 +2950,15 @@ CFGBlock *CFGBuilder::VisitCXXForRangeStmt(CXXForRangeStmt *S) {
     addLocalScopeAndDtors(S->getLoopVarStmt());
 
     // Populate a new block to contain the loop body and loop variable.
-    Block = addStmt(S->getBody());
+    addStmt(S->getBody());
     if (badCFG)
       return 0;
-    Block = addStmt(S->getLoopVarStmt());
+    CFGBlock *LoopVarStmtBlock = addStmt(S->getLoopVarStmt());
     if (badCFG)
       return 0;
     
     // This new body block is a successor to our condition block.
-    addSuccessor(ConditionBlock, KnownVal.isFalse() ? 0 : Block);
+    addSuccessor(ConditionBlock, KnownVal.isFalse() ? 0 : LoopVarStmtBlock);
   }
 
   // Link up the condition block with the code that follows the loop (the
diff --git a/test/Analysis/dead-stores.cpp b/test/Analysis/dead-stores.cpp
index 341363afaa..86d84f0fbf 100644
--- a/test/Analysis/dead-stores.cpp
+++ b/test/Analysis/dead-stores.cpp
@@ -126,3 +126,26 @@ int test_5() {
   return 1;
 }
 
+
+int test_6_aux(unsigned x);
+
+void test_6() {
+  unsigned currDestLen = 0;  // no-warning
+  try {
+    while (test_6_aux(currDestLen)) {
+      currDestLen += 2; // no-warning
+    } 
+  }
+  catch (void *) {}
+}
+
+void test_6b() {
+  unsigned currDestLen = 0;  // no-warning
+  try {
+    while (test_6_aux(currDestLen)) {
+      currDestLen += 2; // expected-warning {{Value stored to 'currDestLen' is never read}}
+      break;
+    } 
+  }
+  catch (void *) {}
+}