[gcc r14-8874] c: Fix boolean conversion of floating constant as integer constant expression [PR113776]

[gcc r14-8874] c: Fix boolean conversion of floating constant as integer constant expression [PR113776]

[Joseph Myers]

https://gcc.gnu.org/g:bfd72bb44eca83b0db2b0bab895f27a8a44247a2

commit r14-8874-gbfd72bb44eca83b0db2b0bab895f27a8a44247a2
Author: Joseph Myers <josmyers@redhat.com>
Date:   Thu Feb 8 01:34:09 2024 +0000

    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.

Diff:
---
 gcc/c/c-typeck.cc                 | 12 +++++++++++-
 gcc/testsuite/gcc.dg/pr113776-1.c |  5 +++++
 gcc/testsuite/gcc.dg/pr113776-2.c |  4 ++++
 gcc/testsuite/gcc.dg/pr113776-3.c |  7 +++++++
 gcc/testsuite/gcc.dg/pr113776-4.c |  6 ++++++
 5 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 3b519c48ae0a..ddeab1e2a8a1 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 000000000000..36190fbc3fec
--- /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 000000000000..9e88210892a4
--- /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 000000000000..c615994a89f6
--- /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 000000000000..1b57557746e1
--- /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 };