[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!

llvm-svn: 251588

1 files changed, 34 insertions, 0 deletions

diff --git a/clang/test/Sema/warn-double-promotion.c b/clang/test/Sema/warn-double-promotion.c
new file mode 100644
index 00000000000..b6fd0c5ec62
--- /dev/null
+++ b/clang/test/Sema/warn-double-promotion.c
@@ -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;
+}