r251588 - [Sema] Implement -Wdouble-promotion for clang.

[George Burgess IV via cfe-commits]

Author: gbiv
Date: Wed Oct 28 19:28:52 2015
New Revision: 251588

URL: http://llvm.org/viewvc/llvm-project?rev=251588&view=rev
Log:
[Sema] Implement -Wdouble-promotion for clang.

GCC has a warning called -Wdouble-promotion, which warns you when
an implicit conversion increases the width of a floating point type.

This is useful when writing code for architectures that can perform
hardware FP ops on floats, but must fall back to software emulation for
larger types (i.e. double, long double).

This fixes PR15109 <https://llvm.org/bugs/show_bug.cgi?id=15109>.

Thanks to Carl Norum for the patch!


Added:
    cfe/trunk/test/Sema/warn-double-promotion.c
Modified:
    cfe/trunk/include/clang/Basic/DiagnosticGroups.td
    cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
    cfe/trunk/lib/Sema/SemaChecking.cpp

Modified: cfe/trunk/include/clang/Basic/DiagnosticGroups.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticGroups.td?rev=251588&r1=251587&r2=251588&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticGroups.td (original)
+++ cfe/trunk/include/clang/Basic/DiagnosticGroups.td Wed Oct 28 19:28:52 2015
@@ -46,6 +46,7 @@ def BoolConversion : DiagGroup<"bool-con
 def IntConversion : DiagGroup<"int-conversion">;
 def EnumConversion : DiagGroup<"enum-conversion">;
 def FloatConversion : DiagGroup<"float-conversion">;
+def DoublePromotion : DiagGroup<"double-promotion">;
 def EnumTooLarge : DiagGroup<"enum-too-large">;
 def UnsupportedNan : DiagGroup<"unsupported-nan">;
 def NonLiteralNullConversion : DiagGroup<"non-literal-null-conversion">;

Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=251588&r1=251587&r2=251588&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
+++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Wed Oct 28 19:28:52 2015
@@ -2590,6 +2590,9 @@ def warn_impcast_complex_scalar : Warnin
 def warn_impcast_float_precision : Warning<
   "implicit conversion loses floating-point precision: %0 to %1">,
   InGroup<Conversion>, DefaultIgnore;
+def warn_impcast_double_promotion : Warning<
+  "implicit conversion increases floating-point precision: %0 to %1">,
+  InGroup<DoublePromotion>, DefaultIgnore;
 def warn_impcast_float_integer : Warning<
   "implicit conversion turns floating-point number into integer: %0 to %1">,
   InGroup<FloatConversion>, DefaultIgnore;

Modified: cfe/trunk/lib/Sema/SemaChecking.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp?rev=251588&r1=251587&r2=251588&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaChecking.cpp (original)
+++ cfe/trunk/lib/Sema/SemaChecking.cpp Wed Oct 28 19:28:52 2015
@@ -7217,6 +7217,14 @@ void CheckImplicitConversion(Sema &S, Ex
           return;
 
         DiagnoseImpCast(S, E, T, CC, diag::warn_impcast_float_precision);
+
+      }
+      // ... or possibly if we're increasing rank, too
+      else if (TargetBT->getKind() > SourceBT->getKind()) {
+        if (S.SourceMgr.isInSystemMacro(CC))
+          return;
+
+        DiagnoseImpCast(S, E, T, CC, diag::warn_impcast_double_promotion);
       }
       return;
     }

Added: cfe/trunk/test/Sema/warn-double-promotion.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/warn-double-promotion.c?rev=251588&view=auto
==============================================================================
--- cfe/trunk/test/Sema/warn-double-promotion.c (added)
+++ cfe/trunk/test/Sema/warn-double-promotion.c Wed Oct 28 19:28:52 2015
@@ -0,0 +1,34 @@
+// RUN: %clang_cc1 -verify -fsyntax-only %s -Wdouble-promotion
+
+float ReturnFloatFromDouble(double d) {
+  return d;
+}
+
+float ReturnFloatFromLongDouble(long double ld) {
+  return ld;
+}
+
+double ReturnDoubleFromLongDouble(long double ld) {
+  return ld;
+}
+
+double ReturnDoubleFromFloat(float f) {
+  return f;  //expected-warning{{implicit conversion increases floating-point precision: 'float' to 'double'}}
+}
+
+long double ReturnLongDoubleFromFloat(float f) {
+  return f;  //expected-warning{{implicit conversion increases floating-point precision: 'float' to 'long double'}}
+}
+
+long double ReturnLongDoubleFromDouble(double d) {
+  return d;  //expected-warning{{implicit conversion increases floating-point precision: 'double' to 'long double'}}
+}
+
+void Convert(float f, double d, long double ld) {
+  d = f;  //expected-warning{{implicit conversion increases floating-point precision: 'float' to 'double'}}
+  ld = f; //expected-warning{{implicit conversion increases floating-point precision: 'float' to 'long double'}}
+  ld = d; //expected-warning{{implicit conversion increases floating-point precision: 'double' to 'long double'}}
+  f = d;
+  f = ld;
+  d = ld;
+}