powerpc: Handle DImode rotatert implemented with rlwinm (PR69946)

Some DImode rotate-right-and-mask can be implemented best with a rlwinm
instruction: those that could be a lshiftrt instead of a rotatert, while
the mask is not right-aligned.  Why the rotate in the testcase is not
optimised to a plain shift is another question, but we need to handle
it here anyway.  We compute the shift amount for a 64-bit rotate.  This
is 32 too high in this case; if we print using %h that is masked out (and
this doesn't silently let through invalid instructions, everything is
checked by rs6000_is_valid_shift_mask which is much more thorough).


	PR target/69946
	* config/rs6000/rs6000.c (rs6000_insn_for_shift_mask): Print rlwinm
	shift amount using %h.  Add comment.

gcc/testsuite/
	* gcc.target/powerpc/pr69946.c: New file.

From-SVN: r233755

gcc/ChangeLog

+2016-02-26  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	PR target/69946
+	* config/rs6000/rs6000.c (rs6000_insn_for_shift_mask): Print rlwinm
+	shift amount using %h.  Add comment.
+
 2016-02-26  Richard Biener  <rguenther@suse.de>
 	    Jeff Law  <law@redhat.com>
 

gcc/config/rs6000/rs6000.c

@@ -17438,9 +17438,12 @@ rs6000_insn_for_shift_mask (machine_mode mode, rtx *operands, bool dot)
 	operands[2] = GEN_INT (32 - INTVAL (operands[2]));
       operands[3] = GEN_INT (31 - nb);
       operands[4] = GEN_INT (31 - ne);
+      /* This insn can also be a 64-bit rotate with mask that really makes
+	 it just a shift right (with mask); the %h below are to adjust for
+	 that situation (shift count is >= 32 in that case).  */
       if (dot)
-	return "rlw%I2nm. %0,%1,%2,%3,%4";
-      return "rlw%I2nm %0,%1,%2,%3,%4";
+	return "rlw%I2nm. %0,%1,%h2,%3,%4";
+      return "rlw%I2nm %0,%1,%h2,%3,%4";
     }
 
   gcc_unreachable ();

gcc/testsuite/ChangeLog

+2016-02-26  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	PR target/69946
+	* gcc.target/powerpc/pr69946.c: New file.
+
 2016-02-26  Richard Biener  <rguenther@suse.de>
             Jeff Law  <law@redhat.com>
 

gcc/testsuite/gcc.target/powerpc/pr69946.c

+/* { dg-do compile { target { powerpc*-*-* && lp64 } } } */
+/* { dg-skip-if "" { powerpc_elfv2 } } */
+/* { dg-options "-O2" } */
+
+/* This generates a rotate:DI by 44, with mask 0xf00, which is implemented
+   using a rlwinm instruction.  We used to write 44 for the shift count
+   there; it should be 12.  */
+
+struct A
+{
+  int a : 4;
+  int : 2;
+  int b : 2;
+  int : 2;
+  int c : 2;
+  int d : 1;
+  int e;
+};
+struct B
+{
+  int a : 4;
+} *a;
+void bar (struct A);
+
+void
+foo (void)
+{
+  struct B b = a[0];
+  struct A c;
+  c.a = b.a;
+  c.b = 1;
+  c.c = 1;
+  c.d = 0;
+  bar (c);
+}
+
+/* { dg-final { scan-assembler-not {(?n)rlwinm.*,44,20,23} } } */
+/* { dg-final { scan-assembler-times {(?n)rlwinm.*,12,20,23} 1 } } */