[GlobalIsel] Canonicalize G_ICMP (#108755)

As a side-effect, we start constant folding icmps.

Split out from #105991.

Author: Thorsten Schütt

llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h

@@ -20,6 +20,7 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/CodeGen/GlobalISel/GenericMachineInstrs.h"
+#include "llvm/CodeGen/GlobalISel/Utils.h"
 #include "llvm/CodeGen/Register.h"
 #include "llvm/CodeGenTypes/LowLevelType.h"
 #include "llvm/IR/InstrTypes.h"
@@ -909,6 +910,8 @@ class CombinerHelper {
   bool matchCastOfBuildVector(const MachineInstr &CastMI,
                               const MachineInstr &BVMI, BuildFnTy &MatchInfo);
 
+  bool matchCanonicalizeICmp(const MachineInstr &MI, BuildFnTy &MatchInfo);
+
 private:
   /// Checks for legality of an indexed variant of \p LdSt.
   bool isIndexedLoadStoreLegal(GLoadStore &LdSt) const;
@@ -1023,6 +1026,9 @@ class CombinerHelper {
   bool tryFoldLogicOfFCmps(GLogicalBinOp *Logic, BuildFnTy &MatchInfo);
 
   bool isCastFree(unsigned Opcode, LLT ToTy, LLT FromTy) const;
+
+  bool constantFoldICmp(const GICmp &ICmp, const GIConstant &LHSCst,
+                        const GIConstant &RHSCst, BuildFnTy &MatchInfo);
 };
 } // namespace llvm
 

llvm/include/llvm/CodeGen/GlobalISel/GenericMachineInstrs.h

@@ -952,6 +952,16 @@ class GExtOrTruncOp : public GCastOp {
   };
 };
 
+/// Represents a splat vector.
+class GSplatVector : public GenericMachineInstr {
+public:
+  Register getScalarReg() const { return getOperand(1).getReg(); }
+
+  static bool classof(const MachineInstr *MI) {
+    return MI->getOpcode() == TargetOpcode::G_SPLAT_VECTOR;
+  };
+};
+
 } // namespace llvm
 
 #endif // LLVM_CODEGEN_GLOBALISEL_GENERICMACHINEINSTRS_H

llvm/include/llvm/CodeGen/GlobalISel/Utils.h

@@ -593,5 +593,44 @@ bool isGuaranteedNotToBeUndef(Register Reg, const MachineRegisterInfo &MRI,
 /// estimate of the type.
 Type *getTypeForLLT(LLT Ty, LLVMContext &C);
 
+/// An integer-like constant.
+///
+/// It abstracts over scalar, fixed-length vectors, and scalable vectors.
+/// In the common case, it provides a common API and feels like an APInt,
+/// while still providing low-level access.
+/// It can be used for constant-folding.
+///
+/// bool isZero()
+/// abstracts over the kind.
+///
+/// switch(const.getKind())
+/// {
+/// }
+/// provides low-level access.
+class GIConstant {
+public:
+  enum class GIConstantKind { Scalar, FixedVector, ScalableVector };
+
+private:
+  GIConstantKind Kind;
+  SmallVector<APInt> Values;
+  APInt Value;
+
+public:
+  GIConstant(ArrayRef<APInt> Values)
+      : Kind(GIConstantKind::FixedVector), Values(Values) {};
+  GIConstant(const APInt &Value, GIConstantKind Kind)
+      : Kind(Kind), Value(Value) {};
+
+  /// Returns the kind of of this constant, e.g, Scalar.
+  GIConstantKind getKind() const { return Kind; }
+
+  /// Returns the value, if this constant is a scalar.
+  APInt getScalarValue() const;
+
+  static std::optional<GIConstant> getConstant(Register Const,
+                                               const MachineRegisterInfo &MRI);
+};
+
 } // End namespace llvm.
 #endif

llvm/include/llvm/Target/GlobalISel/Combine.td

@@ -1007,9 +1007,6 @@ def double_icmp_zero_or_combine: GICombineRule<
          (G_ICMP $root, $p, $ordst, 0))
 >;
 
-def double_icmp_zero_and_or_combine : GICombineGroup<[double_icmp_zero_and_combine,
-                                                      double_icmp_zero_or_combine]>;
-
 def and_or_disjoint_mask : GICombineRule<
   (defs root:$root, build_fn_matchinfo:$info),
   (match (wip_match_opcode G_AND):$root,
@@ -1918,6 +1915,20 @@ def cast_combines: GICombineGroup<[
   integer_of_truncate
 ]>;
 
+def canonicalize_icmp : GICombineRule<
+  (defs root:$root, build_fn_matchinfo:$matchinfo),
+  (match (G_ICMP $root, $pred, $lhs, $rhs):$cmp,
+         [{ return Helper.matchCanonicalizeICmp(*${cmp}, ${matchinfo}); }]),
+  (apply [{ Helper.applyBuildFn(*${cmp}, ${matchinfo}); }])>;
+
+def icmp_combines: GICombineGroup<[
+  canonicalize_icmp,
+  icmp_to_true_false_known_bits,
+  icmp_to_lhs_known_bits,
+  double_icmp_zero_and_combine,
+  double_icmp_zero_or_combine,
+  redundant_binop_in_equality
+]>;
 
 // FIXME: These should use the custom predicate feature once it lands.
 def undef_combines : GICombineGroup<[undef_to_fp_zero, undef_to_int_zero,
@@ -1951,7 +1962,7 @@ def const_combines : GICombineGroup<[constant_fold_fp_ops, const_ptradd_to_i2p,
 
 def known_bits_simplifications : GICombineGroup<[
   redundant_and, redundant_sext_inreg, redundant_or, urem_pow2_to_mask,
-  zext_trunc_fold, icmp_to_true_false_known_bits, icmp_to_lhs_known_bits,
+  zext_trunc_fold,
   sext_inreg_to_zext_inreg]>;
 
 def width_reduction_combines : GICombineGroup<[reduce_shl_of_extend,
@@ -1984,7 +1995,7 @@ def all_combines : GICombineGroup<[integer_reassoc_combines, trivial_combines,
     combine_extracted_vector_load,
     undef_combines, identity_combines, phi_combines,
     simplify_add_to_sub, hoist_logic_op_with_same_opcode_hands, shifts_too_big,
-    reassocs, ptr_add_immed_chain,
+    reassocs, ptr_add_immed_chain, icmp_combines,
     shl_ashr_to_sext_inreg, sext_inreg_of_load,
     width_reduction_combines, select_combines,
     known_bits_simplifications,
@@ -1998,9 +2009,9 @@ def all_combines : GICombineGroup<[integer_reassoc_combines, trivial_combines,
     constant_fold_cast_op, fabs_fneg_fold,
     intdiv_combines, mulh_combines, redundant_neg_operands,
     and_or_disjoint_mask, fma_combines, fold_binop_into_select,
-    sub_add_reg, select_to_minmax, redundant_binop_in_equality,
+    sub_add_reg, select_to_minmax, 
     fsub_to_fneg, commute_constant_to_rhs, match_ands, match_ors,
-    combine_concat_vector, double_icmp_zero_and_or_combine, match_addos,
+    combine_concat_vector, match_addos,
     sext_trunc, zext_trunc, prefer_sign_combines, combine_shuffle_concat]>;
 
 // A combine group used to for prelegalizer combiners at -O0. The combines in

llvm/lib/CodeGen/GlobalISel/CMakeLists.txt

@@ -7,6 +7,7 @@ add_llvm_component_library(LLVMGlobalISel
   Combiner.cpp
   CombinerHelper.cpp
   CombinerHelperCasts.cpp
+  CombinerHelperCompares.cpp
   CombinerHelperVectorOps.cpp
   GIMatchTableExecutor.cpp
   GISelChangeObserver.cpp

llvm/lib/CodeGen/GlobalISel/CombinerHelperCompares.cpp

@@ -0,0 +1,86 @@
+//===- CombinerHelperCompares.cpp------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements CombinerHelper for G_ICMP.
+//
+//===----------------------------------------------------------------------===//
+#include "llvm/CodeGen/GlobalISel/CombinerHelper.h"
+#include "llvm/CodeGen/GlobalISel/GenericMachineInstrs.h"
+#include "llvm/CodeGen/GlobalISel/LegalizerHelper.h"
+#include "llvm/CodeGen/GlobalISel/LegalizerInfo.h"
+#include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
+#include "llvm/CodeGen/GlobalISel/Utils.h"
+#include "llvm/CodeGen/LowLevelTypeUtils.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineOperand.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/TargetOpcodes.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/ErrorHandling.h"
+#include <cstdlib>
+
+#define DEBUG_TYPE "gi-combiner"
+
+using namespace llvm;
+
+bool CombinerHelper::constantFoldICmp(const GICmp &ICmp,
+                                      const GIConstant &LHSCst,
+                                      const GIConstant &RHSCst,
+                                      BuildFnTy &MatchInfo) {
+  if (LHSCst.getKind() != GIConstant::GIConstantKind::Scalar)
+    return false;
+
+  Register Dst = ICmp.getReg(0);
+  LLT DstTy = MRI.getType(Dst);
+
+  if (!isConstantLegalOrBeforeLegalizer(DstTy))
+    return false;
+
+  CmpInst::Predicate Pred = ICmp.getCond();
+  APInt LHS = LHSCst.getScalarValue();
+  APInt RHS = RHSCst.getScalarValue();
+
+  bool Result = ICmpInst::compare(LHS, RHS, Pred);
+
+  MatchInfo = [=](MachineIRBuilder &B) {
+    if (Result)
+      B.buildConstant(Dst, getICmpTrueVal(getTargetLowering(),
+                                          /*IsVector=*/DstTy.isVector(),
+                                          /*IsFP=*/false));
+    else
+      B.buildConstant(Dst, 0);
+  };
+
+  return true;
+}
+
+bool CombinerHelper::matchCanonicalizeICmp(const MachineInstr &MI,
+                                           BuildFnTy &MatchInfo) {
+  const GICmp *Cmp = cast<GICmp>(&MI);
+
+  Register Dst = Cmp->getReg(0);
+  Register LHS = Cmp->getLHSReg();
+  Register RHS = Cmp->getRHSReg();
+
+  CmpInst::Predicate Pred = Cmp->getCond();
+  assert(CmpInst::isIntPredicate(Pred) && "Not an integer compare!");
+  if (auto CLHS = GIConstant::getConstant(LHS, MRI)) {
+    if (auto CRHS = GIConstant::getConstant(RHS, MRI))
+      return constantFoldICmp(*Cmp, *CLHS, *CRHS, MatchInfo);
+
+    // If we have a constant, make sure it is on the RHS.
+    std::swap(LHS, RHS);
+    Pred = CmpInst::getSwappedPredicate(Pred);
+
+    MatchInfo = [=](MachineIRBuilder &B) { B.buildICmp(Pred, Dst, LHS, RHS); };
+    return true;
+  }
+
+  return false;
+}

llvm/lib/CodeGen/GlobalISel/Utils.cpp

@@ -1968,3 +1968,43 @@ Type *llvm::getTypeForLLT(LLT Ty, LLVMContext &C) {
                            Ty.getElementCount());
   return IntegerType::get(C, Ty.getSizeInBits());
 }
+
+APInt llvm::GIConstant::getScalarValue() const {
+  assert(Kind == GIConstantKind::Scalar && "Expected scalar constant");
+
+  return Value;
+}
+
+std::optional<GIConstant>
+llvm::GIConstant::getConstant(Register Const, const MachineRegisterInfo &MRI) {
+  MachineInstr *Constant = getDefIgnoringCopies(Const, MRI);
+
+  if (GSplatVector *Splat = dyn_cast<GSplatVector>(Constant)) {
+    std::optional<ValueAndVReg> MayBeConstant =
+        getIConstantVRegValWithLookThrough(Splat->getScalarReg(), MRI);
+    if (!MayBeConstant)
+      return std::nullopt;
+    return GIConstant(MayBeConstant->Value, GIConstantKind::ScalableVector);
+  }
+
+  if (GBuildVector *Build = dyn_cast<GBuildVector>(Constant)) {
+    SmallVector<APInt> Values;
+    unsigned NumSources = Build->getNumSources();
+    for (unsigned I = 0; I < NumSources; ++I) {
+      Register SrcReg = Build->getSourceReg(I);
+      std::optional<ValueAndVReg> MayBeConstant =
+          getIConstantVRegValWithLookThrough(SrcReg, MRI);
+      if (!MayBeConstant)
+        return std::nullopt;
+      Values.push_back(MayBeConstant->Value);
+    }
+    return GIConstant(Values);
+  }
+
+  std::optional<ValueAndVReg> MayBeConstant =
+      getIConstantVRegValWithLookThrough(Const, MRI);
+  if (!MayBeConstant)
+    return std::nullopt;
+
+  return GIConstant(MayBeConstant->Value, GIConstantKind::Scalar);
+}

llvm/test/CodeGen/AArch64/GlobalISel/combine-canonicalize-icmp.mir

@@ -0,0 +1,95 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -o - -mtriple=aarch64-unknown-unknown -run-pass=aarch64-prelegalizer-combiner -verify-machineinstrs  %s | FileCheck %s --check-prefixes=CHECK
+
+---
+name:            test_icmp_canon
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_icmp_canon
+    ; CHECK: %lhs:_(s64) = G_CONSTANT i64 11
+    ; CHECK-NEXT: %rhs:_(s64) = COPY $x0
+    ; CHECK-NEXT: %res:_(s32) = G_ICMP intpred(sgt), %rhs(s64), %lhs
+    ; CHECK-NEXT: $w0 = COPY %res(s32)
+    %lhs:_(s64) = G_CONSTANT i64 11
+    %rhs:_(s64) = COPY $x0
+    %res:_(s32) = G_ICMP intpred(slt), %lhs(s64), %rhs
+    $w0 = COPY %res(s32)
+...
+---
+name:            test_icmp_no_canon
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_icmp_no_canon
+    ; CHECK: %lhs:_(s64) = COPY $x0
+    ; CHECK-NEXT: %rhs:_(s64) = G_CONSTANT i64 11
+    ; CHECK-NEXT: %res:_(s32) = G_ICMP intpred(slt), %lhs(s64), %rhs
+    ; CHECK-NEXT: $w0 = COPY %res(s32)
+    %lhs:_(s64) = COPY $x0
+    %rhs:_(s64) = G_CONSTANT i64 11
+    %res:_(s32) = G_ICMP intpred(slt), %lhs(s64), %rhs
+    $w0 = COPY %res(s32)
+...
+---
+name:            test_icmp_canon_bv
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_icmp_canon_bv
+    ; CHECK: %opaque1:_(s64) = COPY $x0
+    ; CHECK-NEXT: %opaque2:_(s64) = COPY $x0
+    ; CHECK-NEXT: %const1:_(s64) = G_CONSTANT i64 11
+    ; CHECK-NEXT: %const2:_(s64) = G_CONSTANT i64 12
+    ; CHECK-NEXT: %lhs:_(<2 x s64>) = G_BUILD_VECTOR %const1(s64), %const2(s64)
+    ; CHECK-NEXT: %rhs:_(<2 x s64>) = G_BUILD_VECTOR %opaque1(s64), %opaque2(s64)
+    ; CHECK-NEXT: %res:_(<2 x s32>) = G_ICMP intpred(sgt), %rhs(<2 x s64>), %lhs
+    ; CHECK-NEXT: $x0 = COPY %res(<2 x s32>)
+    %opaque1:_(s64) = COPY $x0
+    %opaque2:_(s64) = COPY $x0
+    %const1:_(s64) = G_CONSTANT i64 11
+    %const2:_(s64) = G_CONSTANT i64 12
+    %lhs:_(<2 x s64>) = G_BUILD_VECTOR %const1(s64), %const2(s64)
+    %rhs:_(<2 x s64>) = G_BUILD_VECTOR %opaque1(s64), %opaque2(s64)
+    %res:_(<2 x s32>) = G_ICMP intpred(slt), %lhs(<2 x s64>), %rhs
+    $x0 = COPY %res(<2 x s32>)
+...
+---
+name:            test_icmp_no_canon_bv_neither_const
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_icmp_no_canon_bv
+    ; CHECK: %opaque1:_(s64) = COPY $x0
+    ; CHECK-NEXT: %opaque2:_(s64) = COPY $x0
+    ; CHECK-NEXT: %const1:_(s64) = G_CONSTANT i64 11
+    ; CHECK-NEXT: %const2:_(s64) = G_CONSTANT i64 12
+    ; CHECK-NEXT: %lhs:_(<2 x s64>) = G_BUILD_VECTOR %const1(s64), %opaque2(s64)
+    ; CHECK-NEXT: %rhs:_(<2 x s64>) = G_BUILD_VECTOR %opaque1(s64), %const2(s64)
+    ; CHECK-NEXT: %res:_(<2 x s32>) = G_ICMP intpred(slt), %lhs(<2 x s64>), %rhs
+    ; CHECK-NEXT: $x0 = COPY %res(<2 x s32>)
+    %opaque1:_(s64) = COPY $x0
+    %opaque2:_(s64) = COPY $x0
+    %const1:_(s64) = G_CONSTANT i64 11
+    %const2:_(s64) = G_CONSTANT i64 12
+    %lhs:_(<2 x s64>) = G_BUILD_VECTOR %const1(s64), %opaque2(s64)
+    %rhs:_(<2 x s64>) = G_BUILD_VECTOR %opaque1(s64), %const2(s64)
+    %res:_(<2 x s32>) = G_ICMP intpred(slt), %lhs(<2 x s64>), %rhs
+    $x0 = COPY %res(<2 x s32>)
+...
+---
+name:            test_icmp_canon_splat
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_icmp_canon_splat
+    ; CHECK: %const:_(s64) = G_CONSTANT i64 11
+    ; CHECK-NEXT: %lhs:_(<vscale x 2 x s64>) = G_SPLAT_VECTOR %const(s64)
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY $x1
+    ; CHECK-NEXT: %rhs:_(<vscale x 2 x s64>) = G_SPLAT_VECTOR [[COPY]](s64)
+    ; CHECK-NEXT: %res:_(<vscale x 2 x s32>) = G_ICMP intpred(sgt), %rhs(<vscale x 2 x s64>), %lhs
+    ; CHECK-NEXT: %z:_(<vscale x 2 x s64>) = G_ZEXT %res(<vscale x 2 x s32>)
+    ; CHECK-NEXT: $z0 = COPY %z(<vscale x 2 x s64>)
+    %const:_(s64) = G_CONSTANT i64 11
+    %lhs:_(<vscale x 2 x s64>) = G_SPLAT_VECTOR %const:_(s64)
+    %1:_(s64) = COPY $x1
+    %rhs:_(<vscale x 2 x s64>) = G_SPLAT_VECTOR %1:_(s64)
+    %res:_(<vscale x 2 x s32>) = G_ICMP intpred(slt), %lhs(<vscale x 2 x s64>), %rhs
+    %z:_(<vscale x 2 x s64>) = G_ZEXT  %res
+    $z0 = COPY %z(<vscale x 2 x s64>)
+...