[RFA] [target/87369] Prefer "bit" over "bfxil"

[Jeff Law]

As I suggested in the BZ, this patch rejects constants with  just the
high bit set for the recently added "bfxil" pattern.  As a result we'll
return to using "bit" for the test in the BZ.

I'm not versed enough in aarch64 performance tuning to know if "bit" is
actually a better choice than "bfxil".  "bit" results in better code for
the testcase, but that seems more a function of register allocation than
"bit" being inherently better than "bfxil".   Obviously someone with
more aarch64 knowledge needs to make a decision here.

My first iteration of the patch changed "aarch64_high_bits_all_ones_p".
We could still go that way too, though the name probably needs to change.

I've bootstrapped and regression tested on aarch64-linux-gnu and it
fixes the regression.  I've also bootstrapped aarch64_be-linux-gnu, but
haven't done any kind of regression tested on that platform.


OK for the trunk?

Jeff
-------------- next part --------------
	PR target/87369
	* config/aarch64/aarch64.md (aarch64_bfxil<mode>): Do not accept
	constant with just the high bit set.  That's better handled by
	the "bit" pattern.

diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
index 88f66104db3..ad6822410c2 100644
--- a/gcc/config/aarch64/aarch64.md
+++ b/gcc/config/aarch64/aarch64.md
@@ -5342,9 +5342,11 @@
 		    (match_operand:GPI 3 "const_int_operand" "n, Ulc"))
 	    (and:GPI (match_operand:GPI 2 "register_operand" "0,r")
 		    (match_operand:GPI 4 "const_int_operand" "Ulc, n"))))]
-  "(INTVAL (operands[3]) == ~INTVAL (operands[4]))
-  && (aarch64_high_bits_all_ones_p (INTVAL (operands[3]))
-    || aarch64_high_bits_all_ones_p (INTVAL (operands[4])))"
+  "(INTVAL (operands[3]) == ~INTVAL (operands[4])
+    && ((aarch64_high_bits_all_ones_p (INTVAL (operands[3]))
+	 && popcount_hwi (INTVAL (operands[3])) != 1)
+        || (aarch64_high_bits_all_ones_p (INTVAL (operands[4]))
+	    && popcount_hwi (INTVAL (operands[4])) != 1)))"
   {
     switch (which_alternative)
     {