[gcc/devel/gccgo] Fix handling of overflow in C casts in integer constant expressions (PR c/93241).

[gcc/devel/gccgo] Fix handling of overflow in C casts in integer constant expressions (PR c/93241).

[Ian Lance Taylor]

https://gcc.gnu.org/g:3d77686d2eddf76d3498169d0ca5653db45a8662

commit 3d77686d2eddf76d3498169d0ca5653db45a8662
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Mon Jan 13 16:39:04 2020 +0000

    Fix handling of overflow in C casts in integer constant expressions (PR c/93241).
    
    Bug 93241 reports a case where certain C expressions involving casts,
    that would not be valid in an evaluated part of an integer constant
    expression (because of e.g. involving integer overflow), are wrongly
    rejected in an unevaluated part of an integer constant expression even
    though all the operands and operations are ones that are valid in that
    context.  This is a rejects-valid regression in GCC 4.5 and later
    relative to 4.4 (for some testcases; the one in the bug uses
    _Static_assert which isn't supported in those older releases).
    
    The rule in the C front end is that an expression with those
    properties (valid in an unevaluated part of an integer constant
    expression but not an evaluated part) must be represented either as an
    INTEGER_CST with TREE_OVERFLOW set or as a C_MAYBE_CONST_EXPR with
    C_MAYBE_CONST_EXPR_INT_OPERANDS set.  This patch fixes build_c_cast to
    check for that case and call note_integer_operands as needed.
    
    Bootstrapped with no regressions for x86_64-pc-linux-gnu.
    
    	PR c/93241
    gcc/c:
    	* c-typeck.c (build_c_cast): Check for expressions with integer
    	operands that can occur in an unevaluated part of an integer
    	constant expression and call note_integer_operands as needed.
    
    gcc/testsuite:
    	* gcc.dg/c11-static-assert-10.c, gcc.dg/c99-const-expr-15.c: New
    	tests.

Diff:
---
 gcc/c/ChangeLog                             |  7 +++++++
 gcc/c/c-typeck.c                            | 10 ++++++++++
 gcc/testsuite/ChangeLog                     |  6 ++++++
 gcc/testsuite/gcc.dg/c11-static-assert-10.c |  9 +++++++++
 gcc/testsuite/gcc.dg/c99-const-expr-15.c    |  9 +++++++++
 5 files changed, 41 insertions(+)

diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog
index d0b6559..b8e807e 100644
--- a/gcc/c/ChangeLog
+++ b/gcc/c/ChangeLog
@@ -1,3 +1,10 @@
+2020-01-13  Joseph Myers  <joseph@codesourcery.com>
+
+	PR c/93241
+	* c-typeck.c (build_c_cast): Check for expressions with integer
+	operands that can occur in an unevaluated part of an integer
+	constant expression and call note_integer_operands as needed.
+
 2019-01-08  Richard Biener  <rguenther@suse.de>
 
 	PR middle-end/93199
diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index c746f23..9866c83 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -5709,6 +5709,8 @@ build_c_cast (location_t loc, tree type, tree expr)
 {
   tree value;
 
+  bool int_operands = EXPR_INT_CONST_OPERANDS (expr);
+
   if (TREE_CODE (expr) == EXCESS_PRECISION_EXPR)
     expr = TREE_OPERAND (expr, 0);
 
@@ -5943,6 +5945,14 @@ build_c_cast (location_t loc, tree type, tree expr)
 	       || TREE_CODE (expr) == COMPLEX_CST)))
       value = build1 (NOP_EXPR, type, value);
 
+  /* If the expression has integer operands and so can occur in an
+     unevaluated part of an integer constant expression, ensure the
+     return value reflects this.  */
+  if (int_operands
+      && INTEGRAL_TYPE_P (type)
+      && !EXPR_INT_CONST_OPERANDS (value))
+    value = note_integer_operands (value);
+
   protected_set_expr_location (value, loc);
   return value;
 }
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index f14638c..976003a 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2020-01-13  Joseph Myers  <joseph@codesourcery.com>
+
+	PR c/93241
+	* gcc.dg/c11-static-assert-10.c, gcc.dg/c99-const-expr-15.c: New
+	tests.
+
 2020-01-13  Martin Sebor  <msebor@redhat.com>
 
 	PR tree-optimization/93213
diff --git a/gcc/testsuite/gcc.dg/c11-static-assert-10.c b/gcc/testsuite/gcc.dg/c11-static-assert-10.c
new file mode 100644
index 0000000..2fe210b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/c11-static-assert-10.c
@@ -0,0 +1,9 @@
+/* Test for constant expressions: casts with integer overflow.  PR
+   c/93241.  */
+/* { dg-do compile } */
+/* { dg-options "-std=c11 -pedantic-errors" } */
+
+#include <limits.h>
+
+_Static_assert (0 ? (_Bool) (INT_MAX + 1) : 1, "");
+_Static_assert (0 ? (short) ((INT_MAX + 1) != 0) : 1, "");
diff --git a/gcc/testsuite/gcc.dg/c99-const-expr-15.c b/gcc/testsuite/gcc.dg/c99-const-expr-15.c
new file mode 100644
index 0000000..b1744b6
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/c99-const-expr-15.c
@@ -0,0 +1,9 @@
+/* Test for constant expressions: casts with integer overflow.  PR
+   c/93241.  */
+/* { dg-do compile } */
+/* { dg-options "-std=c99 -pedantic-errors" } */
+
+#include <limits.h>
+
+struct s { int a : (0 ? (_Bool) (INT_MAX + 1) : 1); };
+struct t { int a : (0 ? (short) ((INT_MAX + 1) != 0) : 1); };