在 2025/6/11 23:53, Richard Sandiford 写道:
Jiawei <jia...@iscas.ac.cn> writes:
This patch adds a new simplification rule to `simplify-rtx.cc` that
handles a common bit manipulation pattern involving a single-bit set
and clear followed by XOR.
The transformation targets RTL of the form:
(xor (and (rotate (~1), A) B) (ashift 1, A))
which is semantically equivalent to:
B | (1 << A)
and can verified by the g++.target/riscv/redundant-bitmap-2.C.
gcc/ChangeLog:
* simplify-rtx.cc (simplify_context::simplify_binary_operation_1):
Handle
more logical simplifications.
---
gcc/simplify-rtx.cc | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
index b34fd2f4b9e..daa46054f83 100644
--- a/gcc/simplify-rtx.cc
+++ b/gcc/simplify-rtx.cc
@@ -4063,6 +4063,19 @@ simplify_context::simplify_binary_operation_1 (rtx_code
code,
&& rtx_equal_p (XEXP (XEXP (op0, 0), 0), op1))
return simplify_gen_binary (IOR, mode, XEXP (op0, 1), op1);
+ /* Convert (xor (and (rotate (~1), A) B) (ashift 1, A))
GCC RTL doesn't use commas :)
+ into B | (1 << A). */
+ if (GET_CODE (op0) == AND
+ && GET_CODE (XEXP (op0, 0)) == ROTATE
+ && CONST_INT_P (XEXP (XEXP (op0, 0), 0))
+ && INTVAL (XEXP (XEXP (op0, 0), 0)) == -2
+ && GET_CODE (op1) == ASHIFT
+ && CONST_INT_P (XEXP (op1, 0))
+ && INTVAL (XEXP (op1, 0)) == 1
+ && rtx_equal_p (XEXP (XEXP (op0, 0), 1), XEXP (op1, 1))
I think you also need to check !side_effects_p on XEXP (op1, 1),
since we'll be dropping one instance of the expression.
+ && rtx_equal_p (XEXP (op0, 1), XEXP (op0, 1)))
Is this last line a typo? It should always be true.
I suppose the main question is whether we can safely apply this for
!SHIFT_COUNT_TRUNCATED targets.
Thanks,
Richard
+ return simplify_gen_binary (IOR, mode, XEXP (op0, 1), op1);
+
tem = simplify_with_subreg_not (code, mode, op0, op1);
if (tem)
return tem;
Thanks for your comments, update in new version.
BR,
Jiawei
