[PATCH] gimple-match: Do not try UNCOND optimization with COND_LEN.

[Robin Dapp <rdapp.gcc@gmail.com>]

Hi,

found in slp-reduc-7.c, this patch prevents optimizing e.g.
 COND_LEN_ADD ({-1, ... }, a, 0, c, len, bias)
unconditionally into just "a".

Currently, we assume that COND_LEN operations can be optimized similarly
to COND operations.  As the length is part of the mask (and usually not
compile-time constant), we must not perform any optimization that relies
on just the mask being "true".

Bootstrap and testsuite are unchanged on aarch64 and x86.

Regards
 Robin

gcc/ChangeLog:

	* gimple-match-exports.cc (maybe_resimplify_conditional_op):
	Check for length masking.
---
 gcc/gimple-match-exports.cc | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/gcc/gimple-match-exports.cc b/gcc/gimple-match-exports.cc
index b36027b0bad..73be9f4f4c3 100644
--- a/gcc/gimple-match-exports.cc
+++ b/gcc/gimple-match-exports.cc
@@ -262,7 +262,8 @@ maybe_resimplify_conditional_op (gimple_seq *seq, gimple_match_op *res_op,
   if (!res_op->cond.cond)
     return false;
 
-  if (!res_op->cond.else_value
+  if (!res_op->cond.len
+      && !res_op->cond.else_value
       && res_op->code.is_tree_code ())
     {
       /* The "else" value doesn't matter.  If the "then" value is a
@@ -301,9 +302,12 @@ maybe_resimplify_conditional_op (gimple_seq *seq, gimple_match_op *res_op,
 
   /* If the "then" value is a gimple value and the "else" value matters,
      create a VEC_COND_EXPR between them, then see if it can be further
-     simplified.  */
+     simplified.
+     Don't do this if we have a COND_LEN_ as that would make us lose the
+     length masking.  */
   gimple_match_op new_op;
-  if (res_op->cond.else_value
+  if (!res_op->cond.len
+      && res_op->cond.else_value
       && VECTOR_TYPE_P (res_op->type)
       && gimple_simplified_result_is_gimple_val (res_op))
     {
@@ -314,7 +318,7 @@ maybe_resimplify_conditional_op (gimple_seq *seq, gimple_match_op *res_op,
       return gimple_resimplify3 (seq, res_op, valueize);
     }
 
-  /* Otherwise try rewriting the operation as an IFN_COND_* call.
+  /* Otherwise try rewriting the operation as an IFN_COND_(LEN_)* call.
      Again, this isn't a simplification in itself, since it's what
      RES_OP already described.  */
   if (convert_conditional_op (res_op, &new_op))
-- 
2.41.0