From a9e8b9e3e90fcfe10a04624a89c39b63c32614d1 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Mon, 2 Jul 2012 23:23:04 +0000
Subject: [PATCH] -Wuninitialized: assume that an
 __attribute__((returns_twice)) function might initialize any variable. This
 is extremely conservative, but is sufficient for now.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@159620 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/UninitializedValues.cpp | 18 ++++++++++++++++++
 test/Sema/uninit-variables.c         | 19 +++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/lib/Analysis/UninitializedValues.cpp b/lib/Analysis/UninitializedValues.cpp
index fbfa46c443..1f97c58946 100644
--- a/lib/Analysis/UninitializedValues.cpp
+++ b/lib/Analysis/UninitializedValues.cpp
@@ -116,6 +116,7 @@ public:
 
   BVPair &getValueVectors(const CFGBlock *block, bool shouldLazyCreate);
 
+  void setAllScratchValues(Value V);
   void mergeIntoScratch(ValueVector const &source, bool isFirst);
   bool updateValueVectorWithScratch(const CFGBlock *block);
   bool updateValueVectors(const CFGBlock *block, const BVPair &newVals);
@@ -240,6 +241,11 @@ static void printVector(const char *name, ValueVector const &bv) {
 }
 #endif
 
+void CFGBlockValues::setAllScratchValues(Value V) {
+  for (unsigned I = 0, E = scratch.size(); I != E; ++I)
+    scratch[I] = V;
+}
+
 void CFGBlockValues::mergeIntoScratch(ValueVector const &source,
                                       bool isFirst) {
   if (isFirst)
@@ -374,6 +380,7 @@ public:
   void reportUse(const Expr *ex, const VarDecl *vd);
 
   void VisitBlockExpr(BlockExpr *be);
+  void VisitCallExpr(CallExpr *ce);
   void VisitDeclStmt(DeclStmt *ds);
   void VisitDeclRefExpr(DeclRefExpr *dr);
   void VisitUnaryOperator(UnaryOperator *uo);
@@ -576,6 +583,17 @@ void TransferFunctions::VisitBlockExpr(BlockExpr *be) {
   }
 }
 
+void TransferFunctions::VisitCallExpr(CallExpr *ce) {
+  // After a call to a function like setjmp or vfork, any variable which is
+  // initialized anywhere within this function may now be initialized. For now,
+  // just assume such a call initializes all variables.
+  // FIXME: Only mark variables as initialized if they have an initializer which
+  // is reachable from here.
+  Decl *Callee = ce->getCalleeDecl();
+  if (Callee && Callee->hasAttr<ReturnsTwiceAttr>())
+    vals.setAllScratchValues(Initialized);
+}
+
 void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
   // Record the last DeclRefExpr seen.  This is an lvalue computation.
   // We use this value to later detect if a variable "escapes" the analysis.
diff --git a/test/Sema/uninit-variables.c b/test/Sema/uninit-variables.c
index 59577b9585..71ce76c3e3 100644
--- a/test/Sema/uninit-variables.c
+++ b/test/Sema/uninit-variables.c
@@ -466,3 +466,22 @@ skip_decl:
     k = produce();
   }
 }
+
+typedef char jmp_buf[256];
+extern int setjmp(jmp_buf env); // implicitly returns_twice
+
+void do_stuff_and_longjmp(jmp_buf env, int *result) __attribute__((noreturn));
+
+int returns_twice() {
+  int a; // expected-note {{initialize}}
+  if (!a) { // expected-warning {{variable 'a' is uninitialized}}
+    jmp_buf env;
+    int b;
+    if (setjmp(env) == 0) {
+      do_stuff_and_longjmp(env, &b);
+    } else {
+      a = b; // no warning
+    }
+  }
+  return a;
+}
-- 
2.40.0