[analyzer] Model casts to bool differently from other numbers.

Casts to bool (and _Bool) are equivalent to checks against zero,
not truncations to 1 bit or 8 bits.

This improved reasoning does cause a change in the behavior of the alpha
BoolAssignment checker. Previously, this checker complained about statements
like "bool x = y" if 'y' was known not to be 0 or 1. Now it does not, since
that conversion is well-defined. It's hard to say what the "best" behavior
here is: this conversion is safe, but might be better written as an explicit
comparison against zero.

More usefully, besides improving our model of booleans, this fixes spurious
warnings when returning the address of a local variable cast to bool.

<rdar://problem/13296133>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@180638 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 11 insertions, 5 deletions

diff --git a/test/Analysis/bool-assignment.c b/test/Analysis/bool-assignment.c
index 86a581def6..0f782fbfd9 100644
--- a/test/Analysis/bool-assignment.c
+++ b/test/Analysis/bool-assignment.c
@@ -1,15 +1,19 @@
 // RUN: %clang_cc1 -analyze -analyzer-checker=core,alpha.core.BoolAssignment -analyzer-store=region -verify -std=c99 -Dbool=_Bool %s
 // RUN: %clang_cc1 -analyze -analyzer-checker=core,alpha.core.BoolAssignment -analyzer-store=region -verify -x c++ %s
 
-// Test C++'s bool and C's _Bool
+// Test C++'s bool and C's _Bool.
+// FIXME: We stopped warning on these when SValBuilder got smarter about
+// casts to bool. Arguably, however, these conversions are okay; the result
+// is always 'true' or 'false'.
 
 void test_stdbool_initialization(int y) {
+  bool constant = 2; // no-warning
   if (y < 0) {
-    bool x = y; // expected-warning {{Assignment of a non-Boolean value}}
+    bool x = y; // no-warning
     return;
   }
   if (y > 1) {
-    bool x = y; // expected-warning {{Assignment of a non-Boolean value}}
+    bool x = y; // no-warning
     return;
   }
   bool x = y; // no-warning
@@ -18,11 +22,11 @@ void test_stdbool_initialization(int y) {
 void test_stdbool_assignment(int y) {
   bool x = 0; // no-warning
   if (y < 0) {
-    x = y; // expected-warning {{Assignment of a non-Boolean value}}
+    x = y; // no-warning
     return;
   }
   if (y > 1) {
-    x = y; // expected-warning {{Assignment of a non-Boolean value}}
+    x = y; // no-warning
     return;
   }
   x = y; // no-warning
@@ -33,6 +37,7 @@ void test_stdbool_assignment(int y) {
 typedef signed char BOOL;
 
 void test_BOOL_initialization(int y) {
+  BOOL constant = 2; // expected-warning {{Assignment of a non-Boolean value}}
   if (y < 0) {
     BOOL x = y; // expected-warning {{Assignment of a non-Boolean value}}
     return;
@@ -63,6 +68,7 @@ void test_BOOL_assignment(int y) {
 typedef unsigned char Boolean;
 
 void test_Boolean_initialization(int y) {
+  Boolean constant = 2; // expected-warning {{Assignment of a non-Boolean value}}
   if (y < 0) {
     Boolean x = y; // expected-warning {{Assignment of a non-Boolean value}}
     return;