From 76f44fbfea1f11e53d4b7e83f0debd029c94a1b3 Mon Sep 17 00:00:00 2001
From: Jakub Jelinek <jakub@redhat.com>
Date: Wed, 19 Apr 2023 11:13:11 +0200
Subject: [PATCH] dse: Use SUBREG_REG for copy_to_mode_reg in DSE replace_read
for WORD_REGISTER_OPERATIONS targets [PR109040]
While we've agreed this is not the right fix for the PR109040 bug,
the patch clearly improves generated code (at least on the testcase from the
PR), so I'd like to propose this as optimization heuristics improvement
for GCC 14.
2023-04-19 Jakub Jelinek <jakub@redhat.com>
PR target/109040
* dse.cc (replace_read): If read_reg is a SUBREG of a word mode
REG, for WORD_REGISTER_OPERATIONS copy SUBREG_REG of it into
a new REG rather than the SUBREG.
---
gcc/dse.cc | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/gcc/dse.cc b/gcc/dse.cc
index a2db8d1cc32f..802b949cfb25 100644
--- a/gcc/dse.cc
+++ b/gcc/dse.cc
@@ -2012,7 +2012,19 @@ replace_read (store_info *store_info, insn_info_t store_insn,
}
/* Force the value into a new register so that it won't be clobbered
between the store and the load. */
- read_reg = copy_to_mode_reg (read_mode, read_reg);
+ if (WORD_REGISTER_OPERATIONS
+ && GET_CODE (read_reg) == SUBREG
+ && REG_P (SUBREG_REG (read_reg))
+ && GET_MODE (SUBREG_REG (read_reg)) == word_mode)
+ {
+ /* For WORD_REGISTER_OPERATIONS with subreg of word_mode register
+ force SUBREG_REG into a new register rather than the SUBREG. */
+ rtx r = copy_to_mode_reg (word_mode, SUBREG_REG (read_reg));
+ read_reg = shallow_copy_rtx (read_reg);
+ SUBREG_REG (read_reg) = r;
+ }
+ else
+ read_reg = copy_to_mode_reg (read_mode, read_reg);
insns = get_insns ();
end_sequence ();
--
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