From: Andrew Pinski <andrew.pinski@oss.qualcomm.com>
Date: Fri, 26 Dec 2025 20:07:26 +0000 (-0800)
Subject: ifcvt: Handle lowpart subregs if noce_emit_cmove fails in noce_try_cond_zero_arith... 
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=92f2a86794ad88d773b102c753e13be1b6f05ff9;p=thirdparty%2Fgcc.git

ifcvt: Handle lowpart subregs if noce_emit_cmove fails in noce_try_cond_zero_arith [PR123308]

This fixes up a missed optimization regression for riscv in ifcvt after r16-6350-g9e61a171244110.
The problem is noce_emit_cmove will fail for QImode. This can show up when dealing with shifts
and the right hand side is `(subreg:QI (reg:DI) lowpart)`. Trying first for the subreg mode
fails so the need to try to unwrap the subreg and try for the full mode.

This fixes test_ShiftLeft_eqz in gcc.target/riscv/zicond_ifcvt_opt.c.

Bootstrapped and tested on x86_64-linux-gnu.

	PR rtl-optimization/123308
gcc/ChangeLog:

	* ifcvt.cc (noce_try_cond_zero_arith): If noce_emit_cmove fails
	for a lowpart subreg case, then try the full reg cmove and
	take the lowpart subreg afterwards.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>
---

diff --git a/gcc/ifcvt.cc b/gcc/ifcvt.cc
index 562775165a2..2b8f68a9b41 100644
--- a/gcc/ifcvt.cc
+++ b/gcc/ifcvt.cc
@@ -3207,6 +3207,28 @@ noce_try_cond_zero_arith (struct noce_if_info *if_info)
 			    XEXP (cond, 0), XEXP (cond, 1),
 			    op != AND ? XEXP (a, 1) : const0_rtx,
 			    op != AND ? const0_rtx : XEXP (a, 0));
+  if (!target)
+    {
+      end_sequence ();
+      rtx tmp = XEXP (a, op != AND);
+      /* If the cmove fails and this was a lowpart subreg,
+	 then try the reg part and then putting back the lowpart
+	 afterwards.  */
+      if (GET_CODE (tmp) != SUBREG  || !subreg_lowpart_p (tmp))
+	return false;
+      start_sequence ();
+
+      tmp = SUBREG_REG (tmp);
+      target = gen_reg_rtx (GET_MODE (tmp));
+      target = noce_emit_cmove (if_info, target, code,
+				XEXP (cond, 0), XEXP (cond, 1),
+				op != AND ? tmp : const0_rtx,
+				op != AND ? const0_rtx : tmp);
+      if (!target)
+	goto end_seq_n_fail;
+      target = rtl_hooks.gen_lowpart_no_emit (GET_MODE (XEXP (a, op != AND)), target);
+      gcc_assert (target);
+    }
   if (!target)
     goto end_seq_n_fail;