convert: Fix test for out of bounds shift count [PR113574]

The following patch is miscompiled, because convert_to_integer_1 for
LSHIFT_EXPR tests if the INTEGER_CST shift count is too high, but
incorrectly compares it against TYPE_SIZE rather than TYPE_PRECISION.
The type in question is unsigned _BitInt(1), which has TYPE_PRECISION 1,
TYPE_SIZE 8, and the shift count is 2 in that case.

2024-01-25  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/113574
	* convert.cc (convert_to_integer_1) <case LSHIFT_EXPR>: Compare shift
	count against TYPE_PRECISION rather than TYPE_SIZE.

	* gcc.dg/torture/bitint-52.c: New test.

diff --git a/gcc/convert.cc b/gcc/convert.cc
index 179f5e690088734764d71236e4b2c1ab1e8283de..5ad24ad2c0851534ae593996ae3ffbb4572ef516 100644 (file)
--- a/gcc/convert.cc
+++ b/gcc/convert.cc
@@ -762,7 +762,8 @@ convert_to_integer_1 (tree type, tree expr, bool dofold)
              {
                /* If shift count is less than the width of the truncated type,
                   really shift.  */
-               if (tree_int_cst_lt (TREE_OPERAND (expr, 1), TYPE_SIZE (type)))
+               if (wi::to_widest (TREE_OPERAND (expr, 1))
+                   < TYPE_PRECISION (type))
                  /* In this case, shifting is like multiplication.  */
                  goto trunc1;
                else

diff --git a/gcc/testsuite/gcc.dg/torture/bitint-52.c b/gcc/testsuite/gcc.dg/torture/bitint-52.c
new file mode 100644 (file)
index 0000000..d2896da
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/bitint-52.c
@@ -0,0 +1,23 @@
+/* PR middle-end/113574 */
+/* { dg-do run { target bitint } } */
+/* { dg-options "-std=c23 -pedantic-errors" } */
+/* { dg-skip-if "" { ! run_expensive_tests }  { "*" } { "-O0" "-O2" } } */
+/* { dg-skip-if "" { ! run_expensive_tests } { "-flto" } { "" } } */
+
+unsigned _BitInt(1) a;
+unsigned _BitInt(8) b;
+
+void
+foo (unsigned _BitInt(16) x)
+{
+  a += (x << 2) | b;
+}
+
+int
+main ()
+{
+  foo (0xfef1uwb);
+  if (a)
+    __builtin_abort ();
+  return 0;
+}