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

1 files changed, 2 insertions, 2 deletions

diff --git a/gcc/genmatch.c b/gcc/genmatch.c
index d6bd90d..0492e80 100644
--- a/gcc/genmatch.c
+++ b/gcc/genmatch.c
@@ -2497,8 +2497,8 @@ expr::gen_transform (FILE *f, int indent, const char *dest, bool gimple,
       /* ???  Building a stmt can fail for various reasons here, seq being
          NULL or the stmt referencing SSA names occuring in abnormal PHIs.
 	 So if we fail here we should continue matching other patterns.  */
-      fprintf_indent (f, indent, "gimple_match_op tem_op (%s, %s",
-		      opr_name, type);
+      fprintf_indent (f, indent, "gimple_match_op tem_op "
+		      "(res_op->cond.any_else (), %s, %s", opr_name, type);
       for (unsigned i = 0; i < ops.length (); ++i)
 	fprintf (f, ", ops%d[%u]", depth, i);
       fprintf (f, ");\n");