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Re: [RFC PATCH] tcg: allow a target to request canonicalization of SUBI
From: |
Richard Henderson |
Subject: |
Re: [RFC PATCH] tcg: allow a target to request canonicalization of SUBI to ADDI |
Date: |
Wed, 25 Oct 2023 13:42:18 -0700 |
User-agent: |
Mozilla Thunderbird |
On 10/25/23 11:59, Paolo Bonzini wrote:
On x86, this is more efficient because it enables generation of
more LEA instructions.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
include/tcg/tcg.h | 4 ++++
tcg/i386/tcg-target.h | 2 ++
tcg/tcg-op.c | 20 ++++++++++++++++----
3 files changed, 22 insertions(+), 4 deletions(-)
diff --git a/include/tcg/tcg.h b/include/tcg/tcg.h
index a9282cdcc60..48e5aeef173 100644
--- a/include/tcg/tcg.h
+++ b/include/tcg/tcg.h
@@ -109,6 +109,10 @@ typedef uint64_t TCGRegSet;
#define TCG_TARGET_HAS_sub2_i32 1
#endif
+#ifndef TCG_TARGET_PREFERS_addi
+#define TCG_TARGET_PREFERS_addi 0
+#endif
I would rather do this unconditionally.
Many of the tcg backends do this manually, e.g. s390x:
case INDEX_op_sub_i64:
a0 = args[0], a1 = args[1], a2 = args[2];
if (const_args[2]) {
a2 = -a2;
goto do_addi_64;
} else {
tcg_out_insn(s, RRFa, SGRK, a0, a1, a2);
}
break;
While we could do something similar for i386, it would be better to not require such hoops
in each backend.
We would also want to perform this transformation in optimize.c.
r~