[14/23] simplify-rtx: Put simplify routines into a class

[Jeff Law]

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