[GlobalISel] Add G_ABDS and G_ABDU instructions (#118122)

The DAG has the same instructions: the signed and unsigned absolute
difference of it's input. For AArch64, they map to uabd and sabd for
Neon and SVE. The Neon and SVE instructions will require custom
patterns.

They are pseudo opcodes and are not imported by the IRTranslator. We
need combines to create them.

PowerPC, ARM, and AArch64 have native instructions.

/// i.e trunc(abs(sext(Op0) - sext(Op1))) becomes abds(Op0, Op1) 
///  or trunc(abs(zext(Op0) - zext(Op1))) becomes abdu(Op0, Op1)

For GlobalISel, we are going to write the combines in MIR patterns.

see:
llvm/test/CodeGen/AArch64/abd-combine.ll

- [ ] combine into abd
- [ ] legalize and add td patterns

Author: Thorsten Schütt

llvm/docs/GlobalISel/GenericOpcode.rst

@@ -474,6 +474,13 @@ undefined.
   %2:_(s33) = G_CTLZ_ZERO_UNDEF %1
   %2:_(s33) = G_CTTZ_ZERO_UNDEF %1
 
+Compute the absolute difference (signed and unsigned), e.g. abs(x-y).
+
+.. code-block:: none
+
+  %0:_(s33) = G_ABDS %2, %3
+  %1:_(s33) = G_ABDU %4, %5
+
 Floating Point Operations
 -------------------------
 

llvm/include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h

@@ -1767,6 +1767,34 @@ class MachineIRBuilder {
     return buildInstr(TargetOpcode::G_MUL, {Dst}, {Src0, Src1}, Flags);
   }
 
+  /// Build and insert \p Res = G_ABDS \p Op0, \p Op1
+  ///
+  /// G_ABDS return the signed absolute difference of \p Op0 and \p Op1.
+  ///
+  /// \pre setBasicBlock or setMI must have been called.
+  /// \pre \p Res, \p Op0 and \p Op1 must be generic virtual registers
+  ///      with the same (scalar or vector) type).
+  ///
+  /// \return a MachineInstrBuilder for the newly created instruction.
+  MachineInstrBuilder buildAbds(const DstOp &Dst, const SrcOp &Src0,
+                                const SrcOp &Src1) {
+    return buildInstr(TargetOpcode::G_ABDS, {Dst}, {Src0, Src1});
+  }
+
+  /// Build and insert \p Res = G_ABDU \p Op0, \p Op1
+  ///
+  /// G_ABDU return the unsigned absolute difference of \p Op0 and \p Op1.
+  ///
+  /// \pre setBasicBlock or setMI must have been called.
+  /// \pre \p Res, \p Op0 and \p Op1 must be generic virtual registers
+  ///      with the same (scalar or vector) type).
+  ///
+  /// \return a MachineInstrBuilder for the newly created instruction.
+  MachineInstrBuilder buildAbdu(const DstOp &Dst, const SrcOp &Src0,
+                                const SrcOp &Src1) {
+    return buildInstr(TargetOpcode::G_ABDU, {Dst}, {Src0, Src1});
+  }
+
   MachineInstrBuilder buildUMulH(const DstOp &Dst, const SrcOp &Src0,
                                  const SrcOp &Src1,
                                  std::optional<unsigned> Flags = std::nullopt) {

llvm/include/llvm/Support/TargetOpcodes.def

@@ -289,6 +289,12 @@ HANDLE_TARGET_OPCODE(G_OR)
 /// Generic bitwise exclusive-or instruction.
 HANDLE_TARGET_OPCODE(G_XOR)
 
+/// Generic absolute difference signed instruction.
+HANDLE_TARGET_OPCODE(G_ABDS)
+
+/// Generic absolute difference unsigned instruction.
+HANDLE_TARGET_OPCODE(G_ABDU)
+
 
 HANDLE_TARGET_OPCODE(G_IMPLICIT_DEF)
 

llvm/include/llvm/Target/GenericOpcodes.td

@@ -386,6 +386,22 @@ def G_ASHR : GenericInstruction {
   let hasSideEffects = false;
 }
 
+// Generic absolute difference signed.
+def G_ABDS : GenericInstruction {
+  let OutOperandList = (outs type0:$dst);
+  let InOperandList = (ins type0:$src1, type0:$src2);
+  let hasSideEffects = false;
+  let isCommutable = true;
+}
+
+// Generic absolute difference unsigned.
+def G_ABDU : GenericInstruction {
+  let OutOperandList = (outs type0:$dst);
+  let InOperandList = (ins type0:$src1, type0:$src2);
+  let hasSideEffects = false;
+  let isCommutable = true;
+}
+
 /// Funnel 'double' shifts take 3 operands, 2 inputs and the shift amount.
 /// fshl(X,Y,Z): (X << (Z % bitwidth)) | (Y >> (bitwidth - (Z % bitwidth)))
 def G_FSHL : GenericInstruction {

llvm/lib/CodeGen/MachineVerifier.cpp

@@ -1585,6 +1585,31 @@ void MachineVerifier::verifyPreISelGenericInstruction(const MachineInstr *MI) {
 
     break;
   }
+  case TargetOpcode::G_ABDS:
+  case TargetOpcode::G_ABDU: {
+    LLT DstTy = MRI->getType(MI->getOperand(0).getReg());
+    LLT SrcTy = MRI->getType(MI->getOperand(1).getReg());
+    LLT SrcTy2 = MRI->getType(MI->getOperand(2).getReg());
+
+    if ((DstTy.isVector() != SrcTy.isVector()) ||
+        (DstTy.isVector() &&
+         DstTy.getElementCount() != SrcTy.getElementCount())) {
+      report("Generic vector abds/abdu must preserve number of lanes", MI);
+      break;
+    }
+
+    if (SrcTy != SrcTy2) {
+      report("Generic abds/abdu must have same input types", MI);
+      break;
+    }
+
+    if (DstTy != SrcTy) {
+      report("Generic abds/abdu must have same input and output types", MI);
+      break;
+    }
+
+    break;
+  }
   case TargetOpcode::G_SCMP:
   case TargetOpcode::G_UCMP: {
     LLT DstTy = MRI->getType(MI->getOperand(0).getReg());

llvm/test/CodeGen/AArch64/GlobalISel/legalizer-info-validation.mir

@@ -70,6 +70,14 @@
 # DEBUG-NEXT: .. the first uncovered type index: 1, OK
 # DEBUG-NEXT: .. the first uncovered imm index: 0, OK
 #
+# DEBUG-NEXT: G_ABDS (opcode 65): 1 type index, 0 imm indices
+# DEBUG-NEXT:.. type index coverage check SKIPPED: no rules defined
+# DEBUG-NEXT:.. imm index coverage check SKIPPED: no rules defined
+#
+# DEBUG-NEXT:G_ABDU (opcode 66): 1 type index, 0 imm indices
+# DEBUG-NEXT:.. type index coverage check SKIPPED: no rules defined
+# DEBUG-NEXT:.. imm index coverage check SKIPPED: no rules defined
+#
 # DEBUG-NEXT: G_IMPLICIT_DEF (opcode {{[0-9]+}}): 1 type index, 0 imm indices
 # DEBUG-NEXT: .. the first uncovered type index: {{[0-9]+}}, OK
 # DEBUG-NEXT: .. the first uncovered imm index: {{[0-9]+}}, OK

llvm/test/CodeGen/RISCV/GlobalISel/legalizer-info-validation.mir

@@ -73,6 +73,14 @@
 # DEBUG-NEXT: .. type index coverage check SKIPPED: user-defined predicate detected
 # DEBUG-NEXT: .. imm index coverage check SKIPPED: user-defined predicate detected
 #
+# DEBUG-NEXT: G_ABDS (opcode 65): 1 type index, 0 imm indices
+# DEBUG-NEXT:.. type index coverage check SKIPPED: no rules defined
+# DEBUG-NEXT:.. imm index coverage check SKIPPED: no rules defined
+#
+# DEBUG-NEXT:G_ABDU (opcode 66): 1 type index, 0 imm indices
+# DEBUG-NEXT:.. type index coverage check SKIPPED: no rules defined
+# DEBUG-NEXT:.. imm index coverage check SKIPPED: no rules defined
+#
 # DEBUG-NEXT: G_IMPLICIT_DEF (opcode {{[0-9]+}}): 1 type index, 0 imm indices
 # DEBUG-NEXT: .. type index coverage check SKIPPED: user-defined predicate detected
 # DEBUG-NEXT: .. imm index coverage check SKIPPED: user-defined predicate detected

llvm/test/MachineVerifier/test_abd_su.mir

@@ -0,0 +1,33 @@
+# RUN: not --crash llc -verify-machineinstrs -mtriple=arm64 -run-pass none -o /dev/null %s 2>&1 | FileCheck %s
+# REQUIRES: aarch64-registered-target
+
+---
+name:            g_abd_su
+body: |
+  bb.0:
+
+    %2:_(p0) = G_IMPLICIT_DEF
+    %3:_(p0) = G_IMPLICIT_DEF
+    %4:_(s1) = G_ABDS %2, %3
+
+    %12:_(s64) = G_IMPLICIT_DEF
+    %13:_(s64) = G_IMPLICIT_DEF
+    %14:_(p0) = G_ABDS %12, %13
+
+    %23:_(<2 x s32>) = G_IMPLICIT_DEF
+    %24:_(<2 x s32>) = G_IMPLICIT_DEF
+    ; CHECK: Generic vector abds/abdu must preserve number of lanes
+    %5:_(s1) = G_ABDU  %23, %24
+
+    %15:_(s32) = G_CONSTANT i32 0
+    %16:_(s64) = G_CONSTANT i64 2
+    ; CHECK: Generic abds/abdu must have same input types
+    %17:_(s1) = G_ABDU %15, %16
+
+    %18:_(s64) = G_CONSTANT i64 0
+    %19:_(s64) = G_CONSTANT i64 2
+    ; CHECK: Generic abds/abdu must have same input and output types
+    %20:_(s1) = G_ABDU %18, %19
+
+...
+

llvm/test/TableGen/GlobalISelEmitter.td

@@ -513,7 +513,7 @@ def : Pat<(frag GPR32:$src1, complex:$src2, complex:$src3),
 // R00O-NEXT:  GIM_Reject,
 // R00O:       // Label [[DEFAULT_NUM]]: @[[DEFAULT]]
 // R00O-NEXT:  GIM_Reject,
-// R00O-NEXT:  }; // Size: 1832 bytes
+// R00O-NEXT:  }; // Size: 1840 bytes
 
 def INSNBOB : I<(outs GPR32:$dst), (ins GPR32:$src1, GPR32:$src2, GPR32:$src3, GPR32:$src4),
                  [(set GPR32:$dst,