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From: Jeff Law <law@redhat.com>
To: gcc-patches@gcc.gnu.org, richard.sandiford@arm.com
Subject: Re: [14/23] simplify-rtx: Put simplify routines into a class
Date: Mon, 30 Nov 2020 12:54:15 -0700	[thread overview]
Message-ID: <f2162d6a-4433-8fa3-396a-7c7ad5857158@redhat.com> (raw)
In-Reply-To: <mptmtzl7jpu.fsf@arm.com>



On 11/13/20 1:18 AM, Richard Sandiford via Gcc-patches wrote:
> One of the recurring warts of RTL is that multiplication by a power
> of 2 is represented as a MULT inside a MEM but as an ASHIFT outside
> a MEM.  It would obviously be better if we didn't have this kind of
> context sensitivity, but it would be difficult to remove.
>
> Currently the simplify-rtx.c routines are hard-coded for the
> ASHIFT form.  This means that some callers have to convert the
> ASHIFTs “back” into MULTs after calling the simplify-rtx.c
> routines; see fwprop.c:canonicalize_address for an example.
>
> I think we can relieve some of the pain by wrapping the simplify-rtx.c
> routines in a simple class that tracks whether the expression occurs
> in a MEM or not, so that no post-processing is needed.
>
> An obvious concern is whether passing the “this” pointer around
> will slow things down or bloat the code.  I can't measure any
> increase in compile time after applying the patch.  Sizewise,
> simplify-rtx.o text increases by 2.3% in default-checking builds
> and 4.1% in release-checking builds.
>
> I realise the MULT/ASHIFT thing isn't the most palatable
> reason for doing this, but I think it might be useful for
> other things in future, such as using local nonzero_bits
> hooks/virtual functions instead of the global hooks.
>
> The obvious alternative would be to add a static variable
> and hope that it is always updated correctly.
I think a static would be step in the wrong direction and I'm generally
in favor using classes, particularly when there's contextual information
we want to query.  Shoving things into a class allows us to reason about
when/how that contextual information is used.



>
> Later patches make use of this.
>
> gcc/
> 	* rtl.h (simplify_context): New class.
> 	(simplify_unary_operation, simplify_binary_operation): Use it.
> 	(simplify_ternary_operation, simplify_relational_operation): Likewise.
> 	(simplify_subreg, simplify_gen_unary, simplify_gen_binary): Likewise.
> 	(simplify_gen_ternary, simplify_gen_relational): Likewise.
> 	(simplify_gen_subreg, lowpart_subreg): Likewise.
> 	* simplify-rtx.c (simplify_gen_binary): Turn into a member function
> 	of simplify_context.
> 	(simplify_gen_unary, simplify_gen_ternary, simplify_gen_relational)
> 	(simplify_truncation, simplify_unary_operation): Likewise.
> 	(simplify_unary_operation_1, simplify_byte_swapping_operation)
> 	(simplify_associative_operation, simplify_logical_relational_operation)
> 	(simplify_binary_operation, simplify_binary_operation_series)
> 	(simplify_distributive_operation, simplify_plus_minus): Likewise.
> 	(simplify_relational_operation, simplify_relational_operation_1)
> 	(simplify_cond_clz_ctz, simplify_merge_mask): Likewise.
> 	(simplify_ternary_operation, simplify_subreg, simplify_gen_subreg)
> 	(lowpart_subreg): Likewise.
> 	(simplify_binary_operation_1): Likewise.  Test mem_depth when
> 	deciding whether the ASHIFT or MULT form is canonical.
> 	(simplify_merge_mask): Use simplify_context.
I like it.  OK for the trunk.

jeff


  reply	other threads:[~2020-11-30 19:54 UTC|newest]

Thread overview: 88+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-13  8:10 [00/23] Make fwprop use an on-the-side RTL SSA representation Richard Sandiford
2020-11-13  8:11 ` [01/23] vec: Silence clang warning Richard Sandiford
2020-11-25 19:58   ` Jeff Law
2020-11-13  8:12 ` [02/23] rtlanal: Remove noop_move_p REG_EQUAL condition Richard Sandiford
2020-11-25 20:00   ` Jeff Law
2020-11-13  8:12 ` [03/23] reginfo: Add a global_reg_set Richard Sandiford
2020-11-25 20:01   ` Jeff Law
2020-11-13  8:13 ` [04/23] Move iterator_range to a new iterator-utils.h file Richard Sandiford
2020-11-25 20:02   ` Jeff Law
2020-11-13  8:13 ` [05/23] Add more iterator utilities Richard Sandiford
2020-11-25 20:12   ` Jeff Law
2020-11-13  8:14 ` [06/23] Add an RAII class for managing obstacks Richard Sandiford
2020-11-25 20:15   ` Jeff Law
2020-11-13  8:14 ` [07/23] Add a class that multiplexes two pointer types Richard Sandiford
2020-11-25 20:23   ` Jeff Law
2020-11-26 16:15     ` Richard Sandiford
2020-11-30  1:28       ` Jeff Law
2020-11-25 23:33   ` Martin Sebor
2020-11-26 17:06     ` Richard Sandiford
2020-11-27 18:12       ` Richard Sandiford
2020-11-28  0:17       ` Martin Sebor
2020-12-17  0:17         ` Richard Sandiford
2020-12-17 14:21           ` Tom Tromey
2020-12-17 15:38             ` Richard Sandiford
2020-12-17 15:44               ` Nathan Sidwell
2021-01-04 15:32                 ` Jeff Law
2020-11-13  8:15 ` [08/23] Add an alternative splay tree implementation Richard Sandiford
2020-12-02 20:36   ` Jeff Law
2020-12-17  0:29     ` Richard Sandiford
2021-01-04 15:27       ` Jeff Law
2021-01-01  8:25   ` Andreas Schwab
2021-01-04 14:53     ` Richard Sandiford
2021-01-04 15:02       ` Andreas Schwab
2021-01-04 15:42         ` Richard Sandiford
2021-01-05 12:13           ` Richard Biener
2020-11-13  8:15 ` [09/23] Add a cut-down version of std::span (array_slice) Richard Sandiford
2020-11-30 19:56   ` Jeff Law
2022-08-03 15:13   ` Martin Jambor
2022-08-03 15:31     ` Richard Sandiford
2022-08-10 16:03   ` Martin Jambor
2022-08-11  6:58     ` Richard Biener
2022-08-16  7:59       ` Richard Sandiford
2020-11-13  8:16 ` [10/23] Tweak the way that is_a is implemented Richard Sandiford
2020-12-02  5:15   ` Jeff Law
2020-11-13  8:16 ` [11/23] Split update_cfg_for_uncondjump out of combine Richard Sandiford
2020-11-30  6:14   ` Jeff Law
2020-11-13  8:17 ` [12/23] Export print-rtl.c:print_insn_with_notes Richard Sandiford
2020-11-25 20:24   ` Jeff Law
2020-11-13  8:18 ` [13/23] recog: Split out a register_asm_p function Richard Sandiford
2020-11-25 20:24   ` Jeff Law
2020-11-13  8:18 ` [14/23] simplify-rtx: Put simplify routines into a class Richard Sandiford
2020-11-30 19:54   ` Jeff Law [this message]
2020-11-13  8:19 ` [15/23] recog: Add a validate_change_xveclen function Richard Sandiford
2020-11-30 20:03   ` Jeff Law
2020-11-13  8:19 ` [16/23] recog: Add a way of temporarily undoing changes Richard Sandiford
2020-11-25 20:27   ` Jeff Law
2020-12-17  0:22     ` Richard Sandiford
2020-11-13  8:20 ` [17/23] recog: Add a class for propagating into insns Richard Sandiford
2020-12-03 22:32   ` Jeff Law
2020-11-13  8:20 ` [18/23] recog: Add an RAII class for undoing insn changes Richard Sandiford
2020-11-25 20:27   ` Jeff Law
2020-11-13  8:20 ` [19/23] rtlanal: Add some new helper classes Richard Sandiford
2020-12-13 17:30   ` Jeff Law
2020-12-14 16:37     ` Richard Sandiford
2020-12-14 20:02       ` Jeff Law
2020-11-13  8:21 ` [20/23] rtlanal: Add simple_regno_set Richard Sandiford
2020-11-25 20:31   ` Jeff Law
2020-12-17  0:47     ` Richard Sandiford
2021-01-04 15:28       ` Jeff Law
2020-11-13  8:22 ` [21/23] doc: Add documentation for rtl-ssa Richard Sandiford
2020-11-30  6:26   ` Jeff Law
2020-11-13  8:23 ` [PATCH 22/23] Add rtl-ssa Richard Sandiford
2020-12-16  3:31   ` Jeff Law
2020-12-17  0:33     ` Richard Sandiford
2020-12-19 20:01       ` Jeff Law
2020-11-13  8:24 ` [PATCH 23/23] fwprop: Rewrite to use RTL SSA Richard Sandiford
2020-12-16  3:52   ` Jeff Law
2020-12-17  0:34     ` Richard Sandiford
2020-11-25 19:58 ` [00/23] Make fwprop use an on-the-side RTL SSA representation Jeff Law
2020-11-26 16:03   ` Richard Sandiford
2020-11-27 15:56     ` Michael Matz
2020-11-27 16:31       ` Richard Sandiford
2020-11-30 21:13         ` Jeff Law
2020-12-01  0:03           ` Michael Matz
2020-12-01 10:15             ` Richard Sandiford
2020-12-02  0:25             ` Jeff Law
2020-11-30  6:45     ` Jeff Law
2020-11-30 14:12       ` Richard Sandiford

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