rs6000: Disassemble opaque modes using subregs to allow optimizations

PR109116  reveals  missed optimizations  when using  unspecs to  extract
vector  components  from opaque-mode  variables. Since RTL optimizers do
not understand unspecs, this leads to redundant register copies. Replace
unspecs with subregs, which  are well understood by RTL passes, allowing
optimizations to take place.

2025-06-30  Peter Bergner  <bergner@linux.ibm.com>

gcc/
	PR target/109116
	* config/rs6000/mma.md (unspec): Delete UNSPEC_MMA_EXTRACT.
	(vsx_disassemble_pair): Expand into a vector register sized subreg.
	(mma_disassemble_acc): Likewise.
	(*vsx_disassemble_pair): Delete.
	(*mma_disassemble_acc): Likewise.

diff --git a/gcc/config/rs6000/mma.md b/gcc/config/rs6000/mma.md
index 50e577ab44d09782d419ebc525f30a9654bff28a..85f3a9266827d4fba88fb965e29ee1fc39ec6c27 100644 (file)
--- a/gcc/config/rs6000/mma.md
+++ b/gcc/config/rs6000/mma.md
@@ -30,7 +30,6 @@
 
 (define_c_enum "unspec"
   [UNSPEC_VSX_ASSEMBLE
-   UNSPEC_MMA_EXTRACT
    UNSPEC_MMA_PMXVBF16GER2
    UNSPEC_MMA_PMXVBF16GER2NN
    UNSPEC_MMA_PMXVBF16GER2NP
@@ -398,29 +397,8 @@
    (match_operand 2 "const_0_to_1_operand")]
   "TARGET_MMA"
 {
-  rtx src;
-  int regoff = INTVAL (operands[2]);
-  src = gen_rtx_UNSPEC (V16QImode,
-                       gen_rtvec (2, operands[1], GEN_INT (regoff)),
-                       UNSPEC_MMA_EXTRACT);
-  emit_move_insn (operands[0], src);
-  DONE;
-})
-
-(define_insn_and_split "*vsx_disassemble_pair"
-  [(set (match_operand:V16QI 0 "mma_disassemble_output_operand" "=mwa")
-       (unspec:V16QI [(match_operand:OO 1 "vsx_register_operand" "wa")
-                     (match_operand 2 "const_0_to_1_operand")]
-                     UNSPEC_MMA_EXTRACT))]
-  "TARGET_MMA
-   && vsx_register_operand (operands[1], OOmode)"
-  "#"
-  "&& reload_completed"
-  [(const_int 0)]
-{
-  int reg = REGNO (operands[1]);
-  int regoff = INTVAL (operands[2]);
-  rtx src = gen_rtx_REG (V16QImode, reg + regoff);
+  int regoff = INTVAL (operands[2]) * 16;
+  rtx src = simplify_gen_subreg (V16QImode, operands[1], OOmode, regoff);
   emit_move_insn (operands[0], src);
   DONE;
 })
@@ -472,29 +450,8 @@
    (match_operand 2 "const_0_to_3_operand")]
   "TARGET_MMA"
 {
-  rtx src;
-  int regoff = INTVAL (operands[2]);
-  src = gen_rtx_UNSPEC (V16QImode,
-                       gen_rtvec (2, operands[1], GEN_INT (regoff)),
-                       UNSPEC_MMA_EXTRACT);
-  emit_move_insn (operands[0], src);
-  DONE;
-})
-
-(define_insn_and_split "*mma_disassemble_acc"
-  [(set (match_operand:V16QI 0 "mma_disassemble_output_operand" "=mwa")
-       (unspec:V16QI [(match_operand:XO 1 "fpr_reg_operand" "d")
-                     (match_operand 2 "const_0_to_3_operand")]
-                     UNSPEC_MMA_EXTRACT))]
-  "TARGET_MMA
-   && fpr_reg_operand (operands[1], XOmode)"
-  "#"
-  "&& reload_completed"
-  [(const_int 0)]
-{
-  int reg = REGNO (operands[1]);
-  int regoff = INTVAL (operands[2]);
-  rtx src = gen_rtx_REG (V16QImode, reg + regoff);
+  int regoff = INTVAL (operands[2]) * 16;
+  rtx src = simplify_gen_subreg (V16QImode, operands[1], XOmode, regoff);
   emit_move_insn (operands[0], src);
   DONE;
 })