[gcc r12-3531] rs6000: Disable optimizing multiple xxsetaccz instructions into one xxsetaccz

[gcc r12-3531] rs6000: Disable optimizing multiple xxsetaccz instructions into one xxsetaccz

[Peter Bergner]

https://gcc.gnu.org/g:f80b9be083e0e7d49e7744b7e531b9aa52acd563

commit r12-3531-gf80b9be083e0e7d49e7744b7e531b9aa52acd563
Author: Peter Bergner <bergner@linux.ibm.com>
Date:   Tue Sep 14 10:47:18 2021 -0500

    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:
---
 gcc/config/rs6000/mma.md                         | 31 ++++++++----------------
 gcc/config/rs6000/rs6000.c                       |  2 +-
 gcc/testsuite/gcc.target/powerpc/mma-builtin-6.c | 14 ++++++-----
 3 files changed, 19 insertions(+), 28 deletions(-)

diff --git a/gcc/config/rs6000/mma.md b/gcc/config/rs6000/mma.md
index 1f6fc03d2ac..1990a2183f6 100644
--- 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 25709375635..b0ec8108007 100644
--- 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 0c6517211e3..715b28138e9 100644
--- 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 } } */