c: Fix boolean conversion of floating constant as integer constant expression [PR113776]

My fix for bug 111059 and bug 111911 caused a conversion of a floating
constant to boolean to wrongly no longer be considered an integer
constant expression, because logic to insert a NOP_EXPR in
c_objc_common_truthvalue_conversion for an argument not an integer
constant expression itself now took place after rather than before the
conversion to bool.  In the specific case of casting a floating
constant to bool, the result is an integer constant expression even
though the argument isn't (build_c_cast deals with ensuring that casts
to integer type of anything of floating type more complicated than a
single floating constant don't get wrongly treated as integer constant
expressions even if they fold to constants), so fix the logic in
c_objc_common_truthvalue_conversion to handle that special case.

Bootstrapped with no regressions for x86_64-pc-linux-gnu.

	PR c/113776

gcc/c
	* c-typeck.cc (c_objc_common_truthvalue_conversion): Return an
	integer constant expression for boolean conversion of floating
	constant.

gcc/testsuite/
	* gcc.dg/pr113776-1.c, gcc.dg/pr113776-2.c, gcc.dg/pr113776-3.c,
	gcc.dg/pr113776-4.c: New tests.

5 files changed, 33 insertions, 1 deletions

diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 3b519c4..ddeab1e 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -13572,7 +13572,17 @@ c_objc_common_truthvalue_conversion (location_t location, tree expr, tree type)
       break;
     }
 
-  int_const = (TREE_CODE (expr) == INTEGER_CST && !TREE_OVERFLOW (expr));
+  /* Conversion of a floating constant to boolean goes through here
+     and yields an integer constant expression.  Otherwise, the result
+     is only an integer constant expression if the argument is.  */
+  int_const = ((TREE_CODE (expr) == INTEGER_CST && !TREE_OVERFLOW (expr))
+	       || ((TREE_CODE (expr) == REAL_CST
+		    || TREE_CODE (expr) == COMPLEX_CST)
+		   && (TREE_CODE (type) == BOOLEAN_TYPE
+		       || (TREE_CODE (type) == ENUMERAL_TYPE
+			   && ENUM_UNDERLYING_TYPE (type) != NULL_TREE
+			   && (TREE_CODE (ENUM_UNDERLYING_TYPE (type))
+			       == BOOLEAN_TYPE)))));
   int_operands = EXPR_INT_CONST_OPERANDS (expr);
   if (int_operands && TREE_CODE (expr) != INTEGER_CST)
     {
diff --git a/gcc/testsuite/gcc.dg/pr113776-1.c b/gcc/testsuite/gcc.dg/pr113776-1.c
new file mode 100644
index 0000000..36190fb
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr113776-1.c
@@ -0,0 +1,5 @@
+/* { dg-do compile } */
+/* { dg-options "-std=c11 -pedantic" } */
+
+char d[(_Bool)0.5 == 1 ? 1 : -1];
+char f[(_Bool)0.0 == 0 ? 1 : -1];
diff --git a/gcc/testsuite/gcc.dg/pr113776-2.c b/gcc/testsuite/gcc.dg/pr113776-2.c
new file mode 100644
index 0000000..9e88210
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr113776-2.c
@@ -0,0 +1,4 @@
+/* { dg-do compile } */
+/* { dg-options "-std=c11 -pedantic" } */
+
+enum e { A = (_Bool) 0.0, B = (_Bool) 0.5, C = (_Bool) 1.0 };
diff --git a/gcc/testsuite/gcc.dg/pr113776-3.c b/gcc/testsuite/gcc.dg/pr113776-3.c
new file mode 100644
index 0000000..c615994
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr113776-3.c
@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-std=c23 -pedantic" } */
+
+enum ebool : bool { BF, BT };
+
+char d[(enum ebool)0.5 == 1 ? 1 : -1];
+char f[(enum ebool)0.0 == 0 ? 1 : -1];
diff --git a/gcc/testsuite/gcc.dg/pr113776-4.c b/gcc/testsuite/gcc.dg/pr113776-4.c
new file mode 100644
index 0000000..1b57557
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr113776-4.c
@@ -0,0 +1,6 @@
+/* { dg-do compile } */
+/* { dg-options "-std=c23 -pedantic" } */
+
+enum ebool : bool { BF, BT };
+
+enum e { A = (enum ebool) 0.0, B = (enum ebool) 0.5, C = (enum ebool) 1.0 };