[PATCH] rtl: Join the insn and split conditions in define_insn_and_split

[Segher Boessenkool]

In theory we could have a split condition not inclusive of the insn
condition in the past.  That never was a good idea, the code does not do
what a non-suspicious reader would think it does.  But it leads to more
serious problems together with iterators: if the split condition (as
written) does not start with "&&", you do not get the insn condition
included in the split condition, and that holds for the part of the insn
condition that was generated by the iterator as well!

This patch simply always joins the two conditions (after the iterators
have done their work) to get the effective split condition.

I tested this on all Linux targets, building the Linux kernel for each,
and it does not change generated code for any of them, so I think we do
not have much breakage to fear.  But it is possible for other targets of
course, and for floating point or vector code, etc.

Is this okay for trunk?


Segher


2021-06-07  Segher Boessenkool  <segher@kernel.crashing.org>

	* gensupport.c (process_rtx) [DEFINE_INSN_AND_SPLIT]: Always include
	the insn condition in the split condition.

---
 gcc/gensupport.c | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/gcc/gensupport.c b/gcc/gensupport.c
index 2cb760ffb90f..8a6345d36470 100644
--- a/gcc/gensupport.c
+++ b/gcc/gensupport.c
@@ -590,7 +590,6 @@ process_rtx (rtx desc, file_location loc)
     case DEFINE_INSN_AND_SPLIT:
     case DEFINE_INSN_AND_REWRITE:
       {
-	const char *split_cond;
 	rtx split;
 	rtvec attr;
 	int i;
@@ -609,17 +608,25 @@ process_rtx (rtx desc, file_location loc)
 	    remove_constraints (XVECEXP (split, 0, i));
 	  }
 
-	/* If the split condition starts with "&&", append it to the
-	   insn condition to create the new split condition.  */
-	split_cond = XSTR (desc, 4);
-	if (split_cond[0] == '&' && split_cond[1] == '&')
+	const char *insn_cond = XSTR (desc, 2);
+	const char *split_cond = XSTR (desc, 4);
+	if (strncmp (split_cond, "&&", 2)
+	    && GET_CODE (desc) == DEFINE_INSN_AND_REWRITE)
+	  error_at (loc, "the rewrite condition must start with `&&'");
+
+	/* If the split condition starts with "&&", skip that.  */
+	if (!strncmp (split_cond, "&&", 2))
 	  {
 	    rtx_reader_ptr->copy_md_ptr_loc (split_cond + 2, split_cond);
-	    split_cond = rtx_reader_ptr->join_c_conditions (XSTR (desc, 2),
-							    split_cond + 2);
+	    split_cond += 2;
 	  }
-	else if (GET_CODE (desc) == DEFINE_INSN_AND_REWRITE)
-	  error_at (loc, "the rewrite condition must start with `&&'");
+
+	/* Always use the conjunction of the given split condition and the
+	   insn condition (which includes stuff from iterators, it is not just
+	   what is given in the pattern in the machine description) as the
+	   split condition to use.  */
+	split_cond = rtx_reader_ptr->join_c_conditions (insn_cond, split_cond);
+
 	XSTR (split, 1) = split_cond;
 	if (GET_CODE (desc) == DEFINE_INSN_AND_REWRITE)
 	  XVEC (split, 2) = gen_rewrite_sequence (XVEC (desc, 1));
-- 
1.8.3.1