rs6000: Disable optimizing multiple xxsetaccz instructions into one xxsetaccz

Fwprop will happily optimize two xxsetaccz instructions into one xxsetaccz
by propagating the results of the first to the uses of the second.
We really don't want that to happen given the late priming/depriming of
accumulators.  I fixed this by making the xxsetaccz source operand an
unspec volatile.  I also removed the mma_xxsetaccz define_expand and
define_insn_and_split and replaced it with a simple define_insn.
The expand and splitter patterns were leftovers from the pre opaque mode
code when the xxsetaccz code was part of the movpxi pattern, and we don't
need them now.

Rather than a new test case, I was able to just modify the current test case
to add another __builtin_mma_xxsetaccz call which shows the bad code gen
with unpatched compilers.

2021-09-14  Peter Bergner  <bergner@linux.ibm.com>

gcc/
	* config/rs6000/mma.md (unspec): Delete UNSPEC_MMA_XXSETACCZ.
	(unspecv): Add UNSPECV_MMA_XXSETACCZ.
	(*mma_xxsetaccz): Delete.
	(mma_xxsetaccz): Change to define_insn.  Remove operand 1.
	Use UNSPECV_MMA_XXSETACCZ.  Update comment.
	* config/rs6000/rs6000.c (rs6000_rtx_costs): Use UNSPECV_MMA_XXSETACCZ.

gcc/testsuite/
	* gcc.target/powerpc/mma-builtin-6.c: Add second call to xxsetacc
	built-in.  Update instruction counts.

diff --git a/gcc/config/rs6000/mma.md b/gcc/config/rs6000/mma.md
index 1f6fc03..1990a21 100644 (file)
--- a/gcc/config/rs6000/mma.md
+++ b/gcc/config/rs6000/mma.md
@@ -91,7 +91,10 @@
    UNSPEC_MMA_XVI8GER4SPP
    UNSPEC_MMA_XXMFACC
    UNSPEC_MMA_XXMTACC
-   UNSPEC_MMA_XXSETACCZ
+  ])
+
+(define_c_enum "unspecv"
+  [UNSPECV_MMA_XXSETACCZ
   ])
 
 ;; MMA instructions with 1 accumulator argument
@@ -467,30 +470,16 @@
   "<acc> %A0"
   [(set_attr "type" "mma")])
 
-;; We can't have integer constants in XOmode so we wrap this in an UNSPEC.
-
-(define_expand "mma_xxsetaccz"
-  [(set (match_operand:XO 0 "fpr_reg_operand")
-       (const_int 0))]
-  "TARGET_MMA"
-{
-  rtx xo0 = gen_rtx_UNSPEC (XOmode, gen_rtvec (1, const0_rtx),
-                           UNSPEC_MMA_XXSETACCZ);
-  emit_insn (gen_rtx_SET (operands[0], xo0));
-  DONE;
-})
+;; We can't have integer constants in XOmode so we wrap this in an
+;; UNSPEC_VOLATILE.
 
-(define_insn_and_split "*mma_xxsetaccz"
+(define_insn "mma_xxsetaccz"
   [(set (match_operand:XO 0 "fpr_reg_operand" "=d")
-       (unspec:XO [(match_operand 1 "const_0_to_1_operand" "O")]
-        UNSPEC_MMA_XXSETACCZ))]
+       (unspec_volatile:XO [(const_int 0)]
+                           UNSPECV_MMA_XXSETACCZ))]
   "TARGET_MMA"
   "xxsetaccz %A0"
-  "&& reload_completed"
-  [(set (match_dup 0) (unspec:XO [(match_dup 1)] UNSPEC_MMA_XXSETACCZ))]
-  ""
-  [(set_attr "type" "mma")
-   (set_attr "length" "4")])
+  [(set_attr "type" "mma")])
 
 (define_insn "mma_<vv>"
   [(set (match_operand:XO 0 "fpr_reg_operand" "=&d")

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index 2570937..b0ec810 100644 (file)
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -22174,7 +22174,7 @@ rs6000_rtx_costs (rtx x, machine_mode mode, int outer_code,
       break;
 
     case UNSPEC:
-      if (XINT (x, 1) == UNSPEC_MMA_XXSETACCZ)
+      if (XINT (x, 1) == UNSPECV_MMA_XXSETACCZ)
        {
          *total = 0;
          return true;

diff --git a/gcc/testsuite/gcc.target/powerpc/mma-builtin-6.c b/gcc/testsuite/gcc.target/powerpc/mma-builtin-6.c
index 0c65172..715b281 100644 (file)
--- a/gcc/testsuite/gcc.target/powerpc/mma-builtin-6.c
+++ b/gcc/testsuite/gcc.target/powerpc/mma-builtin-6.c
@@ -5,14 +5,16 @@
 void
 foo (__vector_quad *dst)
 {
-  __vector_quad acc;
-  __builtin_mma_xxsetaccz (&acc);
-  *dst = acc;
+  __vector_quad acc0, acc1;
+  __builtin_mma_xxsetaccz (&acc0);
+  __builtin_mma_xxsetaccz (&acc1);
+  dst[0] = acc0;
+  dst[1] = acc1;
 }
 
 /* { dg-final { scan-assembler-not {\mlxv\M} } } */
 /* { dg-final { scan-assembler-not {\mlxvp\M} } } */
 /* { dg-final { scan-assembler-not {\mxxmtacc\M} } } */
-/* { dg-final { scan-assembler-times {\mxxsetaccz\M} 1 } } */
-/* { dg-final { scan-assembler-times {\mxxmfacc\M} 1 } } */
-/* { dg-final { scan-assembler-times {\mstxvp\M} 2 } } */
+/* { dg-final { scan-assembler-times {\mxxsetaccz\M} 2 } } */
+/* { dg-final { scan-assembler-times {\mxxmfacc\M} 2 } } */
+/* { dg-final { scan-assembler-times {\mstxvp\M} 4 } } */