lower-bitint: Fix up VIEW_CONVERT_EXPR handling in lower_mergeable_stmt [PR113568]

We generally allow merging mergeable stmts with some final cast (but not
further casts or mergeable operations after the cast).  As some casts
are handled conditionally, if (idx < cst) handle_operand (idx); else if
idx == cst) handle_operand (cst); else ..., we must sure that e.g. the
mergeable PLUS_EXPR/MINUS_EXPR/NEGATE_EXPR never appear in handle_operand
called from such casts, because it ICEs on invalid SSA_NAME form (that part
could be fixable by adding further PHIs) but also because we'd need to
correctly propagate the overflow flags from the if to else if.
So, instead lower_mergeable_stmt handles an outermost widening cast (or
widening cast feeding outermost store) specially.
The problem was similar to PR113408, that VIEW_CONVERT_EXPR tree is
present in the gimple_assign_rhs1 while it is not for NOP_EXPR/CONVERT_EXPR,
so the checks whether the outermost cast should be handled didn't handle
the VCE case and so handle_plus_minus was called from the conditional
handle_cast.

2024-01-27  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/113568
	* gimple-lower-bitint.cc (bitint_large_huge::lower_mergeable_stmt):
	For VIEW_CONVERT_EXPR use first operand of rhs1 instead of rhs1
	in the widening extension checks.

	* gcc.dg/bitint-78.c: New test.

diff --git a/gcc/gimple-lower-bitint.cc b/gcc/gimple-lower-bitint.cc
index 79e3b55a55b549bb67d7e9ba743566f59307af18..6a7ce0ca52756b97551422ec5a70360ca301fe00 100644 (file)
--- a/gcc/gimple-lower-bitint.cc
+++ b/gcc/gimple-lower-bitint.cc
@@ -2401,6 +2401,8 @@ bitint_large_huge::lower_mergeable_stmt (gimple *stmt, tree_code &cmp_code,
       rhs1 = gimple_assign_rhs1 (store_operand
                                 ? SSA_NAME_DEF_STMT (store_operand)
                                 : stmt);
+      if (TREE_CODE (rhs1) == VIEW_CONVERT_EXPR)
+       rhs1 = TREE_OPERAND (rhs1, 0);
       /* Optimize mergeable ops ending with widening cast to _BitInt
         (or followed by store).  We can lower just the limbs of the
         cast operand and widen afterwards.  */

diff --git a/gcc/testsuite/gcc.dg/bitint-78.c b/gcc/testsuite/gcc.dg/bitint-78.c
new file mode 100644 (file)
index 0000000..6c08757
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/bitint-78.c
@@ -0,0 +1,21 @@
+/* PR tree-optimization/113568 */
+/* { dg-do compile { target bitint } } */
+/* { dg-options "-O2 -std=c23" } */
+
+signed char c;
+#if __BITINT_MAXWIDTH__ >= 464
+_BitInt(464) g;
+
+void
+foo (void)
+{
+  _BitInt(464) a[2] = {};
+  _BitInt(464) b;
+  while (c)
+    {
+      b = g + 1;
+      g = a[0];
+      a[0] = b;
+    }
+}
+#endif