ipa-sra: Introduce a mini-DCE to tree-inline.c (PR 93385)

I was asked by Richi to split my fix for PR 93385 for easier review
into IPA-SRA materialization refactoring and the actual DCE addition.
This is the second part that actually contains the DCE of statements
that IPA-SRA should not leave behind because they can have problematic
side effects, even if they are useless, so that we do not depend on
tree-dce to remove them for correctness.

The patch fixes the problem by doing a def-use walk when materializing
clones, marking which statements should not be copied and which
SSA_NAMEs do not need to be computed because eventually they would be
DCEd.  We do this on the original function body and tree-inline simply
does not copy statements which are "dead."

The only complication is removing dead argument calls because that
needs to be communicated to callee redirection code using the
infrastructure introduced by the previous patch.

I added all testcases of the original patch to this one, although some
probably test behavior introduced in the previous patch.

gcc/ChangeLog:

2021-05-12  Martin Jambor  <mjambor@suse.cz>

	PR ipa/93385
	* ipa-param-manipulation.h (class ipa_param_body_adjustments): New
	members m_dead_stmts and m_dead_ssas.
	* ipa-param-manipulation.c
	(ipa_param_body_adjustments::mark_dead_statements): New function.
	(ipa_param_body_adjustments::common_initialization): Call it on
	all removed but not split parameters.
	(ipa_param_body_adjustments::ipa_param_body_adjustments): Initialize
	new mwmbers.
	(ipa_param_body_adjustments::modify_call_stmt): Remove arguments that
	are dead.
	* tree-inline.c (remap_gimple_stmt): Do not copy dead statements, reset
	dead debug statements.
	(copy_phis_for_bb): Do not copy dead PHI nodes.

gcc/testsuite/ChangeLog:

2021-03-22  Martin Jambor  <mjambor@suse.cz>

	PR ipa/93385
	* gcc.dg/ipa/pr93385.c: New test.
	* gcc.dg/ipa/ipa-sra-23.c: Likewise.
	* gcc.dg/ipa/ipa-sra-24.c: Likewise.
	* g++.dg/ipa/ipa-sra-4.C: Likewise.