[analyzer] Add support for pre-C++17 copy elision.

r335795 adds copy elision information to CFG. This commit allows static analyzer
to elide elidable copy constructors by constructing the objects that were
previously subject to elidable copy directly in the target region of the copy.

The chain of elided constructors may potentially be indefinitely long. This
only happens when the object is being returned from a function which in turn is
returned from another function, etc.

NRVO is not supported yet.

Differential Revision: https://reviews.llvm.org/D47671

llvm-svn: 335800

1 files changed, 47 insertions, 111 deletions

diff --git a/clang/test/Analysis/lifetime-extension.cpp b/clang/test/Analysis/lifetime-extension.cpp
index ee55107838d..4337632b31c 100644
--- a/clang/test/Analysis/lifetime-extension.cpp
+++ b/clang/test/Analysis/lifetime-extension.cpp
@@ -97,13 +97,10 @@ void f1() {
 
 void f2() {
   C *after, *before;
-  C c = C(1, &after, &before);
-  clang_analyzer_eval(after == before);
-#ifdef TEMPORARIES
-  // expected-warning@-2{{TRUE}}
-#else
-  // expected-warning@-4{{UNKNOWN}}
-#endif
+  {
+    C c = C(1, &after, &before);
+  }
+  clang_analyzer_eval(after == before); // expected-warning{{TRUE}}
 }
 
 void f3(bool coin) {
@@ -129,6 +126,7 @@ void f4(bool coin) {
   // operator. Ideally also add support for the binary conditional operator in
   // C++. Because for now it calls the constructor for the condition twice.
   if (coin) {
+    // FIXME: Should not warn.
     clang_analyzer_eval(after == before);
 #ifdef TEMPORARIES
   // expected-warning@-2{{The left operand of '==' is a garbage value}}
@@ -136,13 +134,12 @@ void f4(bool coin) {
   // expected-warning@-4{{UNKNOWN}}
 #endif
   } else {
+    // FIXME: Should be TRUE.
     clang_analyzer_eval(after == before);
 #ifdef TEMPORARIES
-    // Seems to work at the moment, but also seems accidental.
-    // Feel free to break.
-  // expected-warning@-4{{TRUE}}
+  // expected-warning@-2{{FALSE}}
 #else
-  // expected-warning@-6{{UNKNOWN}}
+  // expected-warning@-4{{UNKNOWN}}
 #endif
   }
 }
@@ -234,24 +231,25 @@ void f2() {
 } // end namespace maintain_original_object_address_on_move
 
 namespace maintain_address_of_copies {
+class C;
 
-template <typename T> struct AddressVector {
-  const T *buf[10];
+struct AddressVector {
+  C *buf[10];
   int len;
 
   AddressVector() : len(0) {}
 
-  void push(const T *t) {
-    buf[len] = t;
+  void push(C *c) {
+    buf[len] = c;
     ++len;
   }
 };
 
 class C {
-  AddressVector<C> &v;
+  AddressVector &v;
 
 public:
-  C(AddressVector<C> &v) : v(v) { v.push(this); }
+  C(AddressVector &v) : v(v) { v.push(this); }
   ~C() { v.push(this); }
 
 #ifdef MOVES
@@ -267,132 +265,70 @@ public:
 #endif
   } // no-warning
 
-  static C make(AddressVector<C> &v) { return C(v); }
+  static C make(AddressVector &v) { return C(v); }
 };
 
 void f1() {
-  AddressVector<C> v;
+  AddressVector v;
   {
     C c = C(v);
   }
-  // 0. Create the original temporary and lifetime-extend it into variable 'c'
-  //    construction argument.
-  // 1. Construct variable 'c' (elidable copy/move).
-  // 2. Destroy the temporary.
-  // 3. Destroy variable 'c'.
-  clang_analyzer_eval(v.len == 4);
-  clang_analyzer_eval(v.buf[0] == v.buf[2]);
-  clang_analyzer_eval(v.buf[1] == v.buf[3]);
-#ifdef TEMPORARIES
-  // expected-warning@-4{{TRUE}}
-  // expected-warning@-4{{TRUE}}
-  // expected-warning@-4{{TRUE}}
-#else
-  // expected-warning@-8{{UNKNOWN}}
-  // expected-warning@-8{{UNKNOWN}}
-  // expected-warning@-8{{UNKNOWN}}
-#endif
+  // 0. Construct variable 'c' (copy/move elided).
+  // 1. Destroy variable 'c'.
+  clang_analyzer_eval(v.len == 2); // expected-warning{{TRUE}}
+  clang_analyzer_eval(v.buf[0] == v.buf[1]); // expected-warning{{TRUE}}
 }
 
 void f2() {
-  AddressVector<C> v;
+  AddressVector v;
   {
     const C &c = C::make(v);
   }
-  // 0. Construct the original temporary within make(),
-  // 1. Construct the return value of make() (elidable copy/move) and
-  //    lifetime-extend it via reference 'c',
-  // 2. Destroy the temporary within make(),
-  // 3. Destroy the temporary lifetime-extended by 'c'.
-  clang_analyzer_eval(v.len == 4);
-  clang_analyzer_eval(v.buf[0] == v.buf[2]);
-  clang_analyzer_eval(v.buf[1] == v.buf[3]);
+  // 0. Construct the return value of make() (copy/move elided) and
+  //    lifetime-extend it directly via reference 'c',
+  // 1. Destroy the temporary lifetime-extended by 'c'.
+  clang_analyzer_eval(v.len == 2);
+  clang_analyzer_eval(v.buf[0] == v.buf[1]);
 #ifdef TEMPORARIES
-  // expected-warning@-4{{TRUE}}
-  // expected-warning@-4{{TRUE}}
-  // expected-warning@-4{{TRUE}}
+  // expected-warning@-3{{TRUE}}
+  // expected-warning@-3{{TRUE}}
 #else
-  // expected-warning@-8{{UNKNOWN}}
-  // expected-warning@-8{{UNKNOWN}}
-  // expected-warning@-8{{UNKNOWN}}
+  // expected-warning@-6{{UNKNOWN}}
+  // expected-warning@-6{{UNKNOWN}}
 #endif
 }
 
 void f3() {
-  AddressVector<C> v;
+  AddressVector v;
   {
     C &&c = C::make(v);
   }
-  // 0. Construct the original temporary within make(),
-  // 1. Construct the return value of make() (elidable copy/move) and
-  //    lifetime-extend it via reference 'c',
-  // 2. Destroy the temporary within make(),
-  // 3. Destroy the temporary lifetime-extended by 'c'.
-  clang_analyzer_eval(v.len == 4);
-  clang_analyzer_eval(v.buf[0] == v.buf[2]);
-  clang_analyzer_eval(v.buf[1] == v.buf[3]);
+  // 0. Construct the return value of make() (copy/move elided) and
+  //    lifetime-extend it directly via reference 'c',
+  // 1. Destroy the temporary lifetime-extended by 'c'.
+  clang_analyzer_eval(v.len == 2);
+  clang_analyzer_eval(v.buf[0] == v.buf[1]);
 #ifdef TEMPORARIES
-  // expected-warning@-4{{TRUE}}
-  // expected-warning@-4{{TRUE}}
-  // expected-warning@-4{{TRUE}}
+  // expected-warning@-3{{TRUE}}
+  // expected-warning@-3{{TRUE}}
 #else
-  // expected-warning@-8{{UNKNOWN}}
-  // expected-warning@-8{{UNKNOWN}}
-  // expected-warning@-8{{UNKNOWN}}
+  // expected-warning@-6{{UNKNOWN}}
+  // expected-warning@-6{{UNKNOWN}}
 #endif
 }
 
-C doubleMake(AddressVector<C> &v) {
+C doubleMake(AddressVector &v) {
   return C::make(v);
 }
 
 void f4() {
-  AddressVector<C> v;
+  AddressVector v;
   {
     C c = doubleMake(v);
   }
-  // 0. Construct the original temporary within make(),
-  // 1. Construct the return value of make() (elidable copy/move) and
-  //    lifetime-extend it into the return value constructor argument within
-  //    doubleMake(),
-  // 2. Destroy the temporary within make(),
-  // 3. Construct the return value of doubleMake() (elidable copy/move) and
-  //    lifetime-extend it into the variable 'c' constructor argument,
-  // 4. Destroy the return value of make(),
-  // 5. Construct variable 'c' (elidable copy/move),
-  // 6. Destroy the return value of doubleMake(),
-  // 7. Destroy variable 'c'.
-  clang_analyzer_eval(v.len == 8);
-  clang_analyzer_eval(v.buf[0] == v.buf[2]);
-  clang_analyzer_eval(v.buf[1] == v.buf[4]);
-  clang_analyzer_eval(v.buf[3] == v.buf[6]);
-  clang_analyzer_eval(v.buf[5] == v.buf[7]);
-#ifdef TEMPORARIES
-  // expected-warning@-6{{TRUE}}
-  // expected-warning@-6{{TRUE}}
-  // expected-warning@-6{{TRUE}}
-  // expected-warning@-6{{TRUE}}
-  // expected-warning@-6{{TRUE}}
-#else
-  // expected-warning@-12{{UNKNOWN}}
-  // expected-warning@-12{{UNKNOWN}}
-  // expected-warning@-12{{UNKNOWN}}
-  // expected-warning@-12{{UNKNOWN}}
-  // expected-warning@-12{{UNKNOWN}}
-#endif
+  // 0. Construct variable 'c' (all copies/moves elided),
+  // 1. Destroy variable 'c'.
+  clang_analyzer_eval(v.len == 2); // expected-warning{{TRUE}}
+  clang_analyzer_eval(v.buf[0] == v.buf[1]); // expected-warning{{TRUE}}
 }
-
-class NoDtor {
-  AddressVector<NoDtor> &v;
-
-public:
-  NoDtor(AddressVector<NoDtor> &v) : v(v) { v.push(this); }
-};
-
-void f5() {
-  AddressVector<NoDtor> v;
-  const NoDtor &N = NoDtor(v);
-  clang_analyzer_eval(v.buf[0] == &N); // expected-warning{{TRUE}}
-}
-
 } // end namespace maintain_address_of_copies