[llvm] [AArch64][MachineCombiner] Reassociate long chains of accumulation instructions into a tree to increase ILP (PR #126060)

[Jonathan Cohen via llvm-commits]

================
@@ -6674,6 +6674,118 @@ static bool getMaddPatterns(MachineInstr &Root,
   }
   return Found;
 }
+
+bool AArch64InstrInfo::isAccumulationOpcode(unsigned Opcode) const {
+  switch (Opcode) {
+  default:
+    break;
+  case AArch64::UABALB_ZZZ_D:
+  case AArch64::UABALB_ZZZ_H:
+  case AArch64::UABALB_ZZZ_S:
+  case AArch64::UABALT_ZZZ_D:
+  case AArch64::UABALT_ZZZ_H:
+  case AArch64::UABALT_ZZZ_S:
+  case AArch64::UABALv16i8_v8i16:
+  case AArch64::UABALv2i32_v2i64:
+  case AArch64::UABALv4i16_v4i32:
+  case AArch64::UABALv4i32_v2i64:
+  case AArch64::UABALv8i16_v4i32:
+  case AArch64::UABALv8i8_v8i16:
+  case AArch64::UABAv16i8:
+  case AArch64::UABAv2i32:
+  case AArch64::UABAv4i16:
+  case AArch64::UABAv4i32:
+  case AArch64::UABAv8i16:
+  case AArch64::UABAv8i8:
+  case AArch64::SABALv16i8_v8i16:
+  case AArch64::SABALv2i32_v2i64:
+  case AArch64::SABALv4i16_v4i32:
+  case AArch64::SABALv4i32_v2i64:
+  case AArch64::SABALv8i16_v4i32:
+  case AArch64::SABALv8i8_v8i16:
+  case AArch64::SABAv16i8:
+  case AArch64::SABAv2i32:
+  case AArch64::SABAv4i16:
+  case AArch64::SABAv4i32:
+  case AArch64::SABAv8i16:
+  case AArch64::SABAv8i8:
+  case AArch64::MLAv8i8:
+    return true;
+  }
+
+  return false;
+}
+
+std::optional<unsigned> AArch64InstrInfo::getAccumulationStartOpcode(
+    unsigned AccumulationOpcode) const {
+  switch (AccumulationOpcode) {
+  default:
+    llvm_unreachable("Unknown accumulator opcode");
----------------
jcohen-apple wrote:

No, leftovers from an earlier version of the code. Removed. Thanks!

https://github.com/llvm/llvm-project/pull/126060