Re: [PATCH 2/2] Enable elimination of zext/sext

[Kugan <kugan dot vivekanandarajah at linaro dot org>]

>> I added this part of the code (in cfgexpand.c) to handle binary/unary/..
>> gimple operations and used the LHS value range to infer the assigned
>> value range. I will revert this part of the code as this is wrong.
>>
>> I dont think checking promoted_mode for temp will be necessary here as
>> convert_move will handle it correctly if promoted_mode is set for temp.
>>
>> Thus, I will reimplement setting promoted_mode to temp (in
>> expand_expr_real_2) based on the gimple statement content on RHS. i.e.
>> by looking at the RHS operands and its value ranges and by calculating
>> the resulting value range. Does this sound OK to you.
> 
> No, this sounds backward again and won't work because those operands
> again could be just truncated - thus you can't rely on their value-range.
> 
> What you would need is VRP computing value-ranges in the promoted
> mode from the start (and it doesn't do that).


Hi Richard,

Here is an attempt to do the value range computation in promoted_mode's
type when it is overflowing. Bootstrapped on x86-84.

Based on your feedback, I will do more testing on this.

Thanks for your time,
Kugan

ïgcc/ChangeLog:

2014-09-04  Kugan Vivekanandarajah <kuganv@linaro.org>

	* tree-ssa-ccp.c (ccp_finalize): Adjust the nonzero_bits precision to
	the type.
	(evaluate_stmt): Likewise.
	* tree-ssanames.c (set_range_info): Adjust if the precision of stored
	value range is different.
	* tree-vrp.c (normalize_int_cst_precision): New function.
	(set_value_range): Add assert to check precision.
	(set_and_canonicalize_value_range): Call normalize_int_cst_precision
	on min and max.
	(promoted_type): New function.
	(promote_unary_vr): Likewise.
	(promote_binary_vr): Likewise.
	(extract_range_from_binary_expr_1): Adjust type to match value range.
	Store value ranges in promoted type if they overflow.
	(extract_range_from_unary_expr_1): Likewise.
	(adjust_range_with_scev): Call normalize_int_cst_precision
	on min and max.
	(vrp_visit_assignment_or_call): Likewise.
	(simplify_bit_ops_using_ranges): Adjust the value range precision.
	(test_for_singularity): Likewise.
	(simplify_stmt_for_jump_threading): Likewise.
	(extract_range_from_assert): Likewise.

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