Correct warning on Float->Integer conversions.

As identified and briefly discussed here:
https://bugs.llvm.org/show_bug.cgi?id=37305

Converting a floating point number to an integer type when
the integral part is out of the range of the integer type is
undefined behavior in C. Additionally, CodeGen emits an undef
in this situation.

HOWEVER, we've been giving a warning that says that the value is
changed. This patch corrects the warning to list that it is actually
undefined behavior.

Differential Revision: https://reviews.llvm.org/D46535

llvm-svn: 331673

diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 03988a1..a015f45 100644 (file)
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3140,6 +3140,9 @@ def warn_impcast_bitfield_precision_constant : Warning<
 def warn_impcast_literal_float_to_integer : Warning<
   "implicit conversion from %0 to %1 changes value from %2 to %3">,
   InGroup<LiteralConversion>;
+def warn_impcast_literal_float_to_integer_out_of_range : Warning<
+  "implicit conversion of out of range value from %0 to %1 is undefined">,
+  InGroup<LiteralConversion>;
 def warn_impcast_float_integer : Warning<
   "implicit conversion turns floating-point number into integer: %0 to %1">,
   InGroup<FloatConversion>, DefaultIgnore;
@@ -3148,6 +3151,9 @@ def warn_impcast_float_to_integer : Warning<
   "implicit conversion of out of range value from %0 to %1 changes value "
   "from %2 to %3">,
   InGroup<FloatOverflowConversion>, DefaultIgnore;
+def warn_impcast_float_to_integer_out_of_range : Warning<
+  "implicit conversion of out of range value from %0 to %1 is undefined">,
+  InGroup<FloatOverflowConversion>, DefaultIgnore;
 def warn_impcast_float_to_integer_zero : Warning<
   "implicit conversion from %0 to %1 changes non-zero value from %2 to %3">,
   InGroup<FloatZeroConversion>, DefaultIgnore;

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 8cc8330..9652b6e 100644 (file)
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -9429,6 +9429,16 @@ static void DiagnoseFloatingImpCast(Sema &S, Expr *E, QualType T,
 
   unsigned DiagID = 0;
   if (IsLiteral) {
+    // Conversion of a floating-point value to a non-bool integer where the
+    // integral part cannot be represented by the integer type is undefined.
+    if (!IsBool &&
+        ((IntegerValue.isSigned() && (IntegerValue.isMaxSignedValue() ||
+                                      IntegerValue.isMinSignedValue())) ||
+         (IntegerValue.isUnsigned() &&
+          (IntegerValue.isMaxValue() || IntegerValue.isMinValue()))))
+      return DiagnoseImpCast(
+          S, E, T, CContext,
+          diag::warn_impcast_literal_float_to_integer_out_of_range);
     // Warn on floating point literal to integer.
     DiagID = diag::warn_impcast_literal_float_to_integer;
   } else if (IntegerValue == 0) {
@@ -9444,12 +9454,19 @@ static void DiagnoseFloatingImpCast(Sema &S, Expr *E, QualType T,
         return DiagnoseImpCast(S, E, T, CContext,
                                diag::warn_impcast_float_integer, PruneWarnings);
       }
+      if (!IsBool && (IntegerValue.isMaxValue() || IntegerValue.isMinValue()))
+        return DiagnoseImpCast(S, E, T, CContext,
+                               diag::warn_impcast_float_to_integer_out_of_range,
+                               PruneWarnings);
     } else {  // IntegerValue.isSigned()
       if (!IntegerValue.isMaxSignedValue() &&
           !IntegerValue.isMinSignedValue()) {
         return DiagnoseImpCast(S, E, T, CContext,
                                diag::warn_impcast_float_integer, PruneWarnings);
       }
+      return DiagnoseImpCast(S, E, T, CContext,
+                             diag::warn_impcast_float_to_integer_out_of_range,
+                             PruneWarnings);
     }
     // Warn on evaluatable floating point expression to integer conversion.
     DiagID = diag::warn_impcast_float_to_integer;

diff --git a/clang/test/SemaCXX/coroutines.cpp b/clang/test/SemaCXX/coroutines.cpp
index 2c979f5..0d0588d 100644 (file)
--- a/clang/test/SemaCXX/coroutines.cpp
+++ b/clang/test/SemaCXX/coroutines.cpp
@@ -157,7 +157,7 @@ struct coroutine_handle<void> {
 void yield() {
   co_yield 0;
   co_yield {"foo", 1, 2};
-  co_yield {1e100}; // expected-error {{cannot be narrowed}} expected-note {{explicit cast}} expected-warning {{changes value}} expected-warning {{braces around scalar}}
+  co_yield {1e100}; // expected-error {{cannot be narrowed}} expected-note {{explicit cast}} expected-warning {{implicit conversion}} expected-warning {{braces around scalar}}
   co_yield {"foo", __LONG_LONG_MAX__}; // expected-error {{cannot be narrowed}} expected-note {{explicit cast}} expected-warning {{changes value}}
   co_yield {"foo"};
   co_yield "foo"; // expected-error {{no matching}}

diff --git a/clang/test/SemaCXX/warn-float-conversion.cpp b/clang/test/SemaCXX/warn-float-conversion.cpp
index fc22189..cf1ead0 100644 (file)
--- a/clang/test/SemaCXX/warn-float-conversion.cpp
+++ b/clang/test/SemaCXX/warn-float-conversion.cpp
@@ -81,9 +81,9 @@ void TestOverflow() {
   char b = -500.0;  // caught by -Wliteral-conversion
 
   const float LargeNumber = 1024;
-  char c = LargeNumber;  // expected-warning{{implicit conversion of out of range value from 'const float' to 'char' changes value from 1024 to 127}}
-  char d = 400.0 + 400.0;  // expected-warning{{implicit conversion of out of range value from 'double' to 'char' changes value from 800 to 127}}
+  char c = LargeNumber;  // expected-warning{{implicit conversion of out of range value from 'const float' to 'char' is undefined}}
+  char d = 400.0 + 400.0;  // expected-warning{{implicit conversion of out of range value from 'double' to 'char' is undefined}}
 
-  char e = 1.0 / 0.0;  // expected-warning{{implicit conversion of out of range value from 'double' to 'char' changes value from +Inf to 127}}
+  char e = 1.0 / 0.0;  // expected-warning{{implicit conversion of out of range value from 'double' to 'char' is undefined}}
 }
 #endif  // OVERFLOW

diff --git a/clang/test/SemaCXX/warn-literal-conversion.cpp b/clang/test/SemaCXX/warn-literal-conversion.cpp
index 875aa1d..7efcf90 100644 (file)
--- a/clang/test/SemaCXX/warn-literal-conversion.cpp
+++ b/clang/test/SemaCXX/warn-literal-conversion.cpp
@@ -48,4 +48,11 @@ void test1() {
   // values.
   bool b3 = 0.0f;
   bool b4 = 0.0;
+
+  // These all warn because they overflow the target type.
+  short s = 32768.0; // expected-warning{{implicit conversion of out of range value from 'double' to 'short' is undefined}}
+  unsigned short us = 65536.0; // expected-warning{{implicit conversion of out of range value from 'double' to 'unsigned short' is undefined}}
+
+  short s2 = -32769.0; // expected-warning{{implicit conversion of out of range value from 'double' to 'short' is undefined}}
+  unsigned short us2 = -65537.0; // expected-warning{{implicit conversion of out of range value from 'double' to 'unsigned short' is undefined}}
 }