[cfe-commits] r149089 - in /cfe/trunk: lib/Sema/SemaChecking.cpp test/Sema/constant-conversion.c

[Eli Friedman]

Author: efriedma
Date: Thu Jan 26 17:11:39 2012
New Revision: 149089

URL: http://llvm.org/viewvc/llvm-project?rev=149089&view=rev
Log:
Make the bitfield implicit truncation warning slightly more aggressive, and make the printed warning a bit more accurate.  The new behavior matches gcc's -Wconversion.  <rdar://problem/10238797>.


Modified:
    cfe/trunk/lib/Sema/SemaChecking.cpp
    cfe/trunk/test/Sema/constant-conversion.c

Modified: cfe/trunk/lib/Sema/SemaChecking.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp?rev=149089&r1=149088&r2=149089&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaChecking.cpp (original)
+++ cfe/trunk/lib/Sema/SemaChecking.cpp Thu Jan 26 17:11:39 2012
@@ -3655,19 +3655,20 @@
   if (OriginalWidth <= FieldWidth)
     return false;
 
+  // Compute the value which the bitfield will contain.
   llvm::APSInt TruncatedValue = Value.trunc(FieldWidth);
+  TruncatedValue.setIsSigned(Bitfield->getType()->isSignedIntegerType());
 
-  // It's fairly common to write values into signed bitfields
-  // that, if sign-extended, would end up becoming a different
-  // value.  We don't want to warn about that.
-  if (Value.isSigned() && Value.isNegative())
-    TruncatedValue = TruncatedValue.sext(OriginalWidth);
-  else
-    TruncatedValue = TruncatedValue.zext(OriginalWidth);
-
+  // Check whether the stored value is equal to the original value.
+  TruncatedValue = TruncatedValue.extend(OriginalWidth);
   if (Value == TruncatedValue)
     return false;
 
+  // Special-case bitfields of width 1: booleans are naturally 0/1, and
+  // therefore don't strictly fit into a bitfield of width 1.
+  if (FieldWidth == 1 && Value.getBoolValue() == TruncatedValue.getBoolValue())
+    return false;
+
   std::string PrettyValue = Value.toString(10);
   std::string PrettyTrunc = TruncatedValue.toString(10);
 

Modified: cfe/trunk/test/Sema/constant-conversion.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/constant-conversion.c?rev=149089&r1=149088&r2=149089&view=diff
==============================================================================
--- cfe/trunk/test/Sema/constant-conversion.c (original)
+++ cfe/trunk/test/Sema/constant-conversion.c Thu Jan 26 17:11:39 2012
@@ -31,8 +31,8 @@
     int bar : 2;
   };
 
-  struct A a = { 0, 10 };            // expected-warning {{implicit truncation from 'int' to bitfield changes value from 10 to 2}}
-  struct A b[] = { 0, 10, 0, 0 };    // expected-warning {{implicit truncation from 'int' to bitfield changes value from 10 to 2}}
+  struct A a = { 0, 10 };            // expected-warning {{implicit truncation from 'int' to bitfield changes value from 10 to -2}}
+  struct A b[] = { 0, 10, 0, 0 };    // expected-warning {{implicit truncation from 'int' to bitfield changes value from 10 to -2}}
   struct A c[] = {{10, 0}};          // expected-warning {{implicit truncation from 'int' to bitfield changes value from 10 to 2}}
   struct A d = (struct A) { 10, 0 }; // expected-warning {{implicit truncation from 'int' to bitfield changes value from 10 to 2}}
   struct A e = { .foo = 10 };        // expected-warning {{implicit truncation from 'int' to bitfield changes value from 10 to 2}}
@@ -62,3 +62,13 @@
   unsigned char y = 1 ? 65535 : 1; // expected-warning {{changes value}}
 }
 
+void test7() {
+	struct {
+		unsigned int twoBits1:2;
+		unsigned int twoBits2:2;
+		unsigned int reserved:28;
+	} f;
+
+	f.twoBits1 = ~1; // expected-warning {{implicit truncation from 'int' to bitfield changes value from -2 to 2}}
+	f.twoBits2 = ~2; // expected-warning {{implicit truncation from 'int' to bitfield changes value from -3 to 1}}
+}