[llvm] [GlobalIsel] Visit ICmp (PR #105991)

[Jason Eckhardt via llvm-commits]

Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>,
Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>
Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/105991 at github.com>


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+//===- 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/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() != 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;
+
+  switch (Pred) {
+  case CmpInst::Predicate::ICMP_EQ:
+    Result = LHS.eq(RHS);
+    break;
+  case CmpInst::Predicate::ICMP_NE:
+    Result = LHS.ne(RHS);
+    break;
+  case CmpInst::Predicate::ICMP_UGT:
+    Result = LHS.ugt(RHS);
+    break;
+  case CmpInst::Predicate::ICMP_UGE:
+    Result = LHS.uge(RHS);
+    break;
+  case CmpInst::Predicate::ICMP_ULT:
+    Result = LHS.ult(RHS);
+    break;
+  case CmpInst::Predicate::ICMP_ULE:
+    Result = LHS.ule(RHS);
+    break;
+  case CmpInst::Predicate::ICMP_SGT:
+    Result = LHS.sgt(RHS);
+    break;
+  case CmpInst::Predicate::ICMP_SGE:
+    Result = LHS.sge(RHS);
+    break;
+  case CmpInst::Predicate::ICMP_SLT:
+    Result = LHS.slt(RHS);
+    break;
+  case CmpInst::Predicate::ICMP_SLE:
+    Result = LHS.sle(RHS);
+    break;
+  default:
+    llvm_unreachable("Unexpected predicate");
+  }
----------------
nvjle wrote:

Can we replace this entire `switch` with the following?

```
bool Result = ICmpInst::compare(LHS, RHS, Pred);
```


https://github.com/llvm/llvm-project/pull/105991