[llvm] [GlobalIsel] Lower integer constants to constant pool in `LegalizerHelper`. (PR #81957)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-risc-v

Author: Mikhail Gudim (mgudim)

<details>
<summary>Changes</summary>

Extend LegalizerHelper's API to lower integer constants to a load from  constant pool. Previously, this lowering existed only for FP constants.  Apply this change to RISCV.


---
Full diff: https://github.com/llvm/llvm-project/pull/81957.diff


4 Files Affected:

- (modified) llvm/include/llvm/CodeGen/GlobalISel/LegalizerHelper.h (+1) 
- (modified) llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp (+34-13) 
- (modified) llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp (+1-31) 
- (modified) llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.h (-2) 


``````````diff
diff --git a/llvm/include/llvm/CodeGen/GlobalISel/LegalizerHelper.h b/llvm/include/llvm/CodeGen/GlobalISel/LegalizerHelper.h
index a7ecf0dc1ba216..f001d8a1672972 100644
--- a/llvm/include/llvm/CodeGen/GlobalISel/LegalizerHelper.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/LegalizerHelper.h
@@ -365,6 +365,7 @@ class LegalizerHelper {
   LegalizeResult bitcastInsertVectorElt(MachineInstr &MI, unsigned TypeIdx,
                                         LLT CastTy);
 
+  LegalizeResult lowerConstant(MachineInstr &MI);
   LegalizeResult lowerFConstant(MachineInstr &MI);
   LegalizeResult lowerBitcast(MachineInstr &MI);
   LegalizeResult lowerLoad(GAnyLoad &MI);
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 464ff0864d146f..e5450d36cbae51 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -2987,27 +2987,48 @@ static void getUnmergePieces(SmallVectorImpl<Register> &Pieces,
     Pieces.push_back(Unmerge.getReg(I));
 }
 
-LegalizerHelper::LegalizeResult
-LegalizerHelper::lowerFConstant(MachineInstr &MI) {
-  Register Dst = MI.getOperand(0).getReg();
-
+static void emitLoadFromConstantPool(
+    Register DstReg, const Constant *ConstVal,
+    MachineIRBuilder &MIRBuilder) {
+  MachineRegisterInfo &MRI = *MIRBuilder.getMRI();
   MachineFunction &MF = MIRBuilder.getMF();
   const DataLayout &DL = MIRBuilder.getDataLayout();
-
   unsigned AddrSpace = DL.getDefaultGlobalsAddressSpace();
   LLT AddrPtrTy = LLT::pointer(AddrSpace, DL.getPointerSizeInBits(AddrSpace));
-  Align Alignment = Align(DL.getABITypeAlign(
-      getFloatTypeForLLT(MF.getFunction().getContext(), MRI.getType(Dst))));
+  LLT DstLLT = MRI.getType(DstReg);
+
+  Align Alignment(DL.getABITypeAlign(ConstVal->getType()));
 
   auto Addr = MIRBuilder.buildConstantPool(
-      AddrPtrTy, MF.getConstantPool()->getConstantPoolIndex(
-                     MI.getOperand(1).getFPImm(), Alignment));
+      AddrPtrTy,
+      MF.getConstantPool()->getConstantPoolIndex(ConstVal, Alignment));
 
-  MachineMemOperand *MMO = MF.getMachineMemOperand(
-      MachinePointerInfo::getConstantPool(MF), MachineMemOperand::MOLoad,
-      MRI.getType(Dst), Alignment);
+  MachineMemOperand *MMO =
+      MF.getMachineMemOperand(MachinePointerInfo::getConstantPool(MF),
+                              MachineMemOperand::MOLoad, DstLLT, Alignment);
+
+  MIRBuilder.buildLoadInstr(TargetOpcode::G_LOAD, DstReg, Addr, *MMO);
+}
+
+LegalizerHelper::LegalizeResult
+LegalizerHelper::lowerConstant(MachineInstr &MI) {
+  MachineOperand ConstOperand = MI.getOperand(1);
+  assert (ConstOperand.isCImm());
+  const Constant *ConstantVal = ConstOperand.getCImm();
+
+  emitLoadFromConstantPool(MI.getOperand(0).getReg(), ConstantVal, MIRBuilder);
+  MI.eraseFromParent();
+
+  return Legalized;
+}
+
+LegalizerHelper::LegalizeResult
+LegalizerHelper::lowerFConstant(MachineInstr &MI) {
+  MachineOperand ConstOperand = MI.getOperand(1);
+  assert (ConstOperand.isFPImm());
+  const Constant *ConstantVal = ConstOperand.getFPImm();
 
-  MIRBuilder.buildLoadInstr(TargetOpcode::G_LOAD, Dst, Addr, *MMO);
+  emitLoadFromConstantPool(MI.getOperand(0).getReg(), ConstantVal, MIRBuilder);
   MI.eraseFromParent();
 
   return Legalized;
diff --git a/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp b/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
index e852052ce5e602..96e74ee486d6af 100644
--- a/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
+++ b/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
@@ -496,33 +496,6 @@ bool RISCVLegalizerInfo::shouldBeInConstantPool(APInt APImm,
   return !(!SeqLo.empty() && (SeqLo.size() + 2) <= STI.getMaxBuildIntsCost());
 }
 
-// TODO: This is almost the same as LegalizerHelper::lowerFConstant and is
-// target-independent. Should we move this to LegalizeHelper?
-bool RISCVLegalizerInfo::emitLoadFromConstantPool(
-    Register DstReg, const Constant *ConstVal,
-    MachineIRBuilder &MIRBuilder) const {
-  MachineRegisterInfo &MRI = *MIRBuilder.getMRI();
-  MachineFunction &MF = MIRBuilder.getMF();
-  const DataLayout &DL = MIRBuilder.getDataLayout();
-  LLVMContext &Ctx = MF.getFunction().getContext();
-  unsigned AddrSpace = DL.getDefaultGlobalsAddressSpace();
-  LLT AddrPtrTy = LLT::pointer(AddrSpace, DL.getPointerSizeInBits(AddrSpace));
-  LLT DstLLT = MRI.getType(DstReg);
-
-  Align Alignment(DL.getABITypeAlign(getTypeForLLT(DstLLT, Ctx)));
-
-  auto Addr = MIRBuilder.buildConstantPool(
-      AddrPtrTy,
-      MF.getConstantPool()->getConstantPoolIndex(ConstVal, Alignment));
-
-  MachineMemOperand *MMO =
-      MF.getMachineMemOperand(MachinePointerInfo::getConstantPool(MF),
-                              MachineMemOperand::MOLoad, DstLLT, Alignment);
-
-  MIRBuilder.buildLoadInstr(TargetOpcode::G_LOAD, DstReg, Addr, *MMO);
-  return true;
-}
-
 bool RISCVLegalizerInfo::legalizeCustom(
     LegalizerHelper &Helper, MachineInstr &MI,
     LostDebugLocObserver &LocObserver) const {
@@ -544,10 +517,7 @@ bool RISCVLegalizerInfo::legalizeCustom(
     const ConstantInt *ConstVal = MI.getOperand(1).getCImm();
     if (!shouldBeInConstantPool(ConstVal->getValue(), ShouldOptForSize))
       return true;
-    emitLoadFromConstantPool(MI.getOperand(0).getReg(),
-                             MI.getOperand(1).getCImm(), MIRBuilder);
-    MI.eraseFromParent();
-    return true;
+    return Helper.lowerConstant(MI);
   }
   case TargetOpcode::G_SHL:
   case TargetOpcode::G_ASHR:
diff --git a/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.h b/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.h
index 046555f3a3e9ee..323426034827e4 100644
--- a/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.h
+++ b/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.h
@@ -38,8 +38,6 @@ class RISCVLegalizerInfo : public LegalizerInfo {
 
 private:
   bool shouldBeInConstantPool(APInt APImm, bool ShouldOptForSize) const;
-  bool emitLoadFromConstantPool(Register DstReg, const Constant *CPVal,
-                                MachineIRBuilder &MIRBuilder) const;
   bool legalizeShlAshrLshr(MachineInstr &MI, MachineIRBuilder &MIRBuilder,
                            GISelChangeObserver &Observer) const;
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/81957