Extend tree code folds to IFN_COND_*

This patch adds match.pd support for applying normal folds to their
IFN_COND_* forms.  E.g. the rule:

  (plus @0 (negate @1)) -> (minus @0 @1)

also allows the fold:

  (IFN_COND_ADD @0 @1 (negate @2) @3) -> (IFN_COND_SUB @0 @1 @2 @3)

Actually doing this by direct matches in gimple-match.c would
probably lead to combinatorial explosion, so instead, the patch
makes gimple_match_op carry a condition under which the operation
happens ("cond"), and the value to use when the condition is false
("else_value").  Thus in the example above we'd do the following

(a) convert:

      cond:NULL_TREE (IFN_COND_ADD @0 @1 @4 @3) else_value:NULL_TREE

    to:

      cond:@0 (plus @1 @4) else_value:@3

(b) apply gimple_resimplify to (plus @1 @4)

(c) reintroduce cond and else_value when constructing the result.

Nested operations inherit the condition of the outer operation
(so that we don't introduce extra faults) but have a null else_value.
If we try to build such an operation, the target gets to choose what
else_value it can handle efficiently: obvious choices include one of
the operands or a zero constant.  (The alternative would be to have some
representation for an undefined value, but that seems a bit invasive,
and isn't likely to be useful here.)

I've made the condition a mandatory part of the gimple_match_op
constructor so that it doesn't accidentally get dropped.

2018-07-12  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* target.def (preferred_else_value): New target hook.
	* doc/tm.texi.in (TARGET_PREFERRED_ELSE_VALUE): New hook.
	* doc/tm.texi: Regenerate.
	* targhooks.h (default_preferred_else_value): Declare.
	* targhooks.c (default_preferred_else_value): New function.
	* internal-fn.h (conditional_internal_fn_code): Declare.
	* internal-fn.c (FOR_EACH_CODE_MAPPING): New macro.
	(get_conditional_internal_fn): Use it.
	(conditional_internal_fn_code): New function.
	* gimple-match.h (gimple_match_cond): New struct.
	(gimple_match_op): Add a cond member function.
	(gimple_match_op::gimple_match_op): Update all forms to take a
	gimple_match_cond.
	* genmatch.c (expr::gen_transform): Use the same condition as res_op
	for the suboperation, but don't specify a particular else_value.
	* tree-ssa-sccvn.c (vn_nary_simplify, vn_reference_lookup_3)
	(visit_nary_op, visit_reference_op_load): Pass
	gimple_match_cond::UNCOND to the gimple_match_op constructor.
	* gimple-match-head.c: Include tree-eh.h
	(convert_conditional_op): New function.
	(maybe_resimplify_conditional_op): Likewise.
	(gimple_resimplify1): Call maybe_resimplify_conditional_op.
	(gimple_resimplify2): Likewise.
	(gimple_resimplify3): Likewise.
	(gimple_resimplify4): Likewise.
	(maybe_push_res_to_seq): Return null for conditional operations.
	(try_conditional_simplification): New function.
	(gimple_simplify): Call it.  Pass conditions to the gimple_match_op
	constructor.
	* match.pd: Fold VEC_COND_EXPRs of an IFN_COND_* call to a new
	IFN_COND_* call.
	* config/aarch64/aarch64.c (aarch64_preferred_else_value): New
	function.
	(TARGET_PREFERRED_ELSE_VALUE): Redefine.

gcc/testsuite/
	* gcc.dg/vect/vect-cond-arith-2.c: New test.
	* gcc.target/aarch64/sve/loop_add_6.c: Likewise.

From-SVN: r262586

2 files changed, 18 insertions, 0 deletions

diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 7e2cdc2..ff6d514 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -6048,6 +6048,22 @@ expanded sequence has been inserted.  This hook is also responsible
 for allocating any storage for reductions when necessary.
 @end deftypefn
 
+@deftypefn {Target Hook} tree TARGET_PREFERRED_ELSE_VALUE (unsigned @var{ifn}, tree @var{type}, unsigned @var{nops}, tree *@var{ops})
+This hook returns the target's preferred final argument for a call
+to conditional internal function @var{ifn} (really of type
+@code{internal_fn}).  @var{type} specifies the return type of the
+function and @var{ops} are the operands to the conditional operation,
+of which there are @var{nops}.
+
+For example, if @var{ifn} is @code{IFN_COND_ADD}, the hook returns
+a value of type @var{type} that should be used when @samp{@var{ops}[0]}
+and @samp{@var{ops}[1]} are conditionally added together.
+
+This hook is only relevant if the target supports conditional patterns
+like @code{cond_add@var{m}}.  The default implementation returns a zero
+constant of type @var{type}.
+@end deftypefn
+
 @node Anchored Addresses
 @section Anchored Addresses
 @cindex anchored addresses
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index b7b0e8a..2f97151 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -4149,6 +4149,8 @@ address;  but often a machine-dependent strategy can generate better code.
 
 @hook TARGET_GOACC_REDUCTION
 
+@hook TARGET_PREFERRED_ELSE_VALUE
+
 @node Anchored Addresses
 @section Anchored Addresses
 @cindex anchored addresses