[PATCH], PR target/87033, General LWAX on PowerPC

[Michael Meissner]

In this patch earlier to improve switch behavior:
https://gcc.gnu.org/ml/gcc-patches/2018-07/msg01957.html

I noticed that the compiler wasn't generating the LWAX instruction.  I tracked
this down to the "extendsi<mode>2" insn using the "Y" constraint when it can
optimize a load + sign extend into a single load with sign extend.  The "Y"
constraint is for DS-form offsettable addresses, and does not allow indexed
addresses (i.e. X-form loads).  This patch adds the "Z" constraint as well,
which allows indexed addresses.

I have down trunk builds with/without this patch and there were no regressions.
Can I apply this patch to the trunk?  Can I backport this patch to GCC 7 and
GCC 8 as well with a suitable delay to catch any problems?

[gcc]
2018-08-20  Michael Meissner  <meissner@linux.ibm.com>

	PR target/87033
	* config/rs6000/rs6000.md (extendsi<mode>2): Change constraints
	from 'Y' to 'YZ' to enable the LWAX instruction to be generated
	for indexed loads.

[gcc/testsuite]
2018-08-20  Michael Meissner  <meissner@linux.ibm.com>

	PR target/87033
	* gcc.target/powerpc/pr87033.c: New test.

-- 
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA
email: meissner@linux.ibm.com, phone: +1 (978) 899-4797
-------------- next part --------------
Index: gcc/config/rs6000/rs6000.md
===================================================================
--- gcc/config/rs6000/rs6000.md	(revision 263672)
+++ gcc/config/rs6000/rs6000.md	(working copy)
@@ -988,7 +988,7 @@ (define_insn "extendsi<mode>2"
 		     "=r, r,   wl,    wu,    wj,    wK,     wH,    wr")
 
 	(sign_extend:EXTSI (match_operand:SI 1 "lwa_operand"
-		     "Y,  r,   Z,     Z,     r,     wK,     wH,    ?wIwH")))]
+		     "YZ, r,   Z,     Z,     r,     wK,     wH,    ?wIwH")))]
   ""
   "@
    lwa%U1%X1 %0,%1
Index: gcc/testsuite/gcc.target/powerpc/pr87033.c
===================================================================
--- gcc/testsuite/gcc.target/powerpc/pr87033.c	(nonexistent)
+++ gcc/testsuite/gcc.target/powerpc/pr87033.c	(working copy)
@@ -0,0 +1,11 @@
+/* { dg-do compile { target { powerpc*-*-* && lp64 } } } */
+/* { dg-options "-O2" } */
+
+/* Insure that a LWAX is generated instead of ADD + LWA.  */
+long func (int *p, unsigned long n)
+{
+  return p[n];
+}
+
+/* { dg-final { scan-assembler     {\mlwax\M} } } */
+/* { dg-final { scan-assembler-not {\mlwa\M}  } } */