Hi!
On top of the just posted patch, the following patch attempts to
use value range to see if MSB is known to be false and for scalar integral
extension in that case tries to expand both sign and zero extension and
chooses based on RTX costs the cheaper one (if the costs are the same
uses what it used before, TYPE_UNSIGNED (TREE_TYPE (treeop0)) based.
The patch regresses the gcc.target/i386/pr78103-3.c test, will post
a separate patch for that momentarily (with the intent that if all 3
patches are approved, I'll commit the PR78103 related one before this one).
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2025-06-06 Jakub Jelinek <ja...@redhat.com>
PR middle-end/120434
* expr.cc (expand_expr_real_2) <CASE_CONVERT>: If get_range_pos_neg
at -O2 for scalar integer extension suggests the most significant
bit of op0 is not set, try both unsigned and signed conversion and
choose the cheaper one. If both are the same cost, choose one
based on TYPE_UNSIGNED (TREE_TYPE (treeop0)).
* gcc.target/i386/pr120434-2.c: New test.
--- gcc/expr.cc.jj 2025-06-05 10:36:06.545069723 +0200
+++ gcc/expr.cc 2025-06-05 19:14:45.601489036 +0200
@@ -9885,14 +9885,68 @@ expand_expr_real_2 (const_sepops ops, rt
op0 = gen_rtx_fmt_e (TYPE_UNSIGNED (TREE_TYPE (treeop0))
? ZERO_EXTEND : SIGN_EXTEND, mode, op0);
+ else if (SCALAR_INT_MODE_P (GET_MODE (op0))
+ && optimize >= 2
+ && SCALAR_INT_MODE_P (mode)
+ && (GET_MODE_SIZE (as_a <scalar_int_mode> (mode))
+ > GET_MODE_SIZE (as_a <scalar_int_mode> (GET_MODE (op0))))
+ && get_range_pos_neg (treeop0,
+ currently_expanding_gimple_stmt) == 1)
+ {
+ /* If argument is known to be positive when interpreted
+ as signed, we can expand it as both sign and zero
+ extension. Choose the cheaper sequence in that case. */
+ bool speed_p = optimize_insn_for_speed_p ();
+ rtx uns_ret = NULL_RTX, sgn_ret = NULL_RTX;
+ do_pending_stack_adjust ();
+ start_sequence ();
+ if (target == NULL_RTX)
+ uns_ret = convert_to_mode (mode, op0, 1);
+ else
+ convert_move (target, op0, 1);
+ rtx_insn *uns_insns = end_sequence ();
+ start_sequence ();
+ if (target == NULL_RTX)
+ sgn_ret = convert_to_mode (mode, op0, 0);
+ else
+ convert_move (target, op0, 0);
+ rtx_insn *sgn_insns = end_sequence ();
+ unsigned uns_cost = seq_cost (uns_insns, speed_p);
+ unsigned sgn_cost = seq_cost (sgn_insns, speed_p);
+ bool was_tie = false;
+
+ /* If costs are the same then use as tie breaker the other other
+ factor. */
+ if (uns_cost == sgn_cost)
+ {
+ uns_cost = seq_cost (uns_insns, !speed_p);
+ sgn_cost = seq_cost (sgn_insns, !speed_p);
+ was_tie = true;
+ }
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, ";; positive extension:%s unsigned cost: %u; "
+ "signed cost: %u\n",
+ was_tie ? " (needed tie breaker)" : "",
+ uns_cost, sgn_cost);
+ if (uns_cost < sgn_cost
+ || (uns_cost == sgn_cost && TYPE_UNSIGNED (TREE_TYPE (treeop0))))
+ {
+ emit_insn (uns_insns);
+ sgn_ret = uns_ret;
+ }
+ else
+ emit_insn (sgn_insns);
+ if (target == NULL_RTX)
+ op0 = sgn_ret;
+ else
+ op0 = target;
+ }
else if (target == 0)
- op0 = convert_to_mode (mode, op0,
- TYPE_UNSIGNED (TREE_TYPE
- (treeop0)));
+ op0 = convert_to_mode (mode, op0, TYPE_UNSIGNED (TREE_TYPE (treeop0)));
else
{
- convert_move (target, op0,
- TYPE_UNSIGNED (TREE_TYPE (treeop0)));
+ convert_move (target, op0, TYPE_UNSIGNED (TREE_TYPE (treeop0)));
op0 = target;
}
--- gcc/testsuite/gcc.target/i386/pr120434-2.c.jj 2025-06-06
11:41:49.829197752 +0200
+++ gcc/testsuite/gcc.target/i386/pr120434-2.c 2025-06-06 11:40:25.294236198
+0200
@@ -0,0 +1,15 @@
+/* PR middle-end/120434 */
+/* { dg-do compile { target lp64 } } */
+/* { dg-options "-O2 -mtune=generic -masm=att" } */
+/* { dg-final { scan-assembler-not "\tmovslq\t%edi, %rdi" } } */
+/* { dg-final { scan-assembler "\tmovl\t%edi, %edi" } } */
+
+extern unsigned long long foo (unsigned long long x);
+
+unsigned long long
+bar (int x)
+{
+ if (x < 50)
+ return 0;
+ return foo (x);
+}
Jakub
