[PATCH] Only allow (int)trunc(x) to (int)x simplification with -ffp-int-builtin-inexact [PR107723]

[Xi Ruoyao]

With -fno-fp-int-builtin-inexact, trunc is not allowed to raise
FE_INEXACT and it should produce an integral result (if the input is not
NaN or Inf).  Thus FE_INEXACT should not be raised.

But (int)x may raise FE_INEXACT when x is a non-integer, non-NaN, and
non-Inf value.  C23 recommends to do so in a footnote.

Thus we should not simplify (int)trunc(x) to (int)x if
-fno-fp-int-builtin-inexact.

gcc/ChangeLog:

        PR middle-end/107723
        * convert.cc (convert_to_integer_1) [case BUILT_IN_TRUNC]: Break
        early if !flag_fp_int_builtin_inexact.

gcc/testsuite/ChangeLog:

        PR middle-end/107723
        * gcc.dg/torture/builtin-fp-int-inexact-trunc.c: New test.
---

Bootstrapped and regtested on x86_64-linux-gnu.  Ok for trunk?

 gcc/convert.cc                                       |  3 ++-
 .../gcc.dg/torture/builtin-fp-int-inexact-trunc.c    | 12 ++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/builtin-fp-int-inexact-trunc.c

diff --git a/gcc/convert.cc b/gcc/convert.cc
index 46c8bcb31f8..31f63ea783b 100644
--- a/gcc/convert.cc
+++ b/gcc/convert.cc
@@ -591,7 +591,8 @@ convert_to_integer_1 (tree type, tree expr, bool dofold)
        CASE_FLT_FN (BUILT_IN_TRUNC):
        CASE_FLT_FN_FLOATN_NX (BUILT_IN_TRUNC):
          if (call_expr_nargs (s_expr) != 1
-             || !SCALAR_FLOAT_TYPE_P (TREE_TYPE (CALL_EXPR_ARG (s_expr, 0))))
+             || !SCALAR_FLOAT_TYPE_P (TREE_TYPE (CALL_EXPR_ARG (s_expr, 0)))
+             || !flag_fp_int_builtin_inexact)
            break;
          return convert_to_integer_1 (type, CALL_EXPR_ARG (s_expr, 0),
                                       dofold);
diff --git a/gcc/testsuite/gcc.dg/torture/builtin-fp-int-inexact-trunc.c 
b/gcc/testsuite/gcc.dg/torture/builtin-fp-int-inexact-trunc.c
new file mode 100644
index 00000000000..09731183621
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/builtin-fp-int-inexact-trunc.c
@@ -0,0 +1,12 @@
+/* Test -fno-fp-int-builtin-inexact.  */
+/* { dg-do compile } */
+/* { dg-options "-fno-fp-int-builtin-inexact -fdump-tree-original" } */
+
+long
+x (double y)
+{
+  return __builtin_trunc (y);
+}
+
+/* Optimization should not discard the __builtin_trunc call.  */
+/* { dg-final { scan-tree-dump "__builtin_trunc" "original" } } */
-- 
2.43.0