[RISCV][GISel] Add manual instruction selection for i8/i16/i32->i32/i64 G_SEXT/G_ZEXT. (#161971)

Because GISel doesn't distinquish integer and FP types, we need to allow
s16/s32 as legal inputs/outputs of G_SEXT and G_ZEXT.

This requires a extra isel patterns to support the cross product of
these types that we don't need for SelectionDAG. We also needed to add
i16/i32 to the GPR register class which prevents some type inferencing
in tablegen and increases the size of the RISCVGenDAGISel.inc by 2K.

This patch proposes to do manual selection so we can remove these
patterns and eventually remove the types from the register class.

Author: topperc

llvm/lib/Target/RISCV/GISel/RISCVInstructionSelector.cpp

@@ -736,6 +736,62 @@ bool RISCVInstructionSelector::select(MachineInstr &MI) {
     MI.eraseFromParent();
     return true;
   }
+  case TargetOpcode::G_ZEXT:
+  case TargetOpcode::G_SEXT: {
+    bool IsSigned = Opc != TargetOpcode::G_ZEXT;
+    Register DstReg = MI.getOperand(0).getReg();
+    Register SrcReg = MI.getOperand(1).getReg();
+    LLT SrcTy = MRI->getType(SrcReg);
+    unsigned SrcSize = SrcTy.getSizeInBits();
+
+    if (SrcTy.isVector())
+      return false; // Should be handled by imported patterns.
+
+    assert((*RBI.getRegBank(DstReg, *MRI, TRI)).getID() ==
+               RISCV::GPRBRegBankID &&
+           "Unexpected ext regbank");
+
+    // Use addiw SrcReg, 0 (sext.w) for i32.
+    if (IsSigned && SrcSize == 32) {
+      MI.setDesc(TII.get(RISCV::ADDIW));
+      MI.addOperand(MachineOperand::CreateImm(0));
+      return constrainSelectedInstRegOperands(MI, TII, TRI, RBI);
+    }
+
+    // Use add.uw SrcReg, X0 (zext.w) for i32 with Zba.
+    if (!IsSigned && SrcSize == 32 && STI.hasStdExtZba()) {
+      MI.setDesc(TII.get(RISCV::ADD_UW));
+      MI.addOperand(MachineOperand::CreateReg(RISCV::X0, /*isDef=*/false));
+      return constrainSelectedInstRegOperands(MI, TII, TRI, RBI);
+    }
+
+    // Use sext.h/zext.h for i16 with Zbb.
+    if (SrcSize == 16 && STI.hasStdExtZbb()) {
+      MI.setDesc(TII.get(IsSigned       ? RISCV::SEXT_H
+                         : STI.isRV64() ? RISCV::ZEXT_H_RV64
+                                        : RISCV::ZEXT_H_RV32));
+      return constrainSelectedInstRegOperands(MI, TII, TRI, RBI);
+    }
+
+    // Use pack(w) SrcReg, X0 for i16 zext with Zbkb.
+    if (!IsSigned && SrcSize == 16 && STI.hasStdExtZbkb()) {
+      MI.setDesc(TII.get(STI.is64Bit() ? RISCV::PACKW : RISCV::PACK));
+      MI.addOperand(MachineOperand::CreateReg(RISCV::X0, /*isDef=*/false));
+      return constrainSelectedInstRegOperands(MI, TII, TRI, RBI);
+    }
+
+    // Fall back to shift pair.
+    auto ShiftLeft =
+        MIB.buildInstr(RISCV::SLLI, {&RISCV::GPRRegClass}, {SrcReg})
+            .addImm(STI.getXLen() - SrcSize);
+    constrainSelectedInstRegOperands(*ShiftLeft, TII, TRI, RBI);
+    auto ShiftRight = MIB.buildInstr(IsSigned ? RISCV::SRAI : RISCV::SRLI,
+                                     {DstReg}, {ShiftLeft})
+                          .addImm(STI.getXLen() - SrcSize);
+    constrainSelectedInstRegOperands(*ShiftRight, TII, TRI, RBI);
+    MI.eraseFromParent();
+    return true;
+  }
   case TargetOpcode::G_FCONSTANT: {
     // TODO: Use constant pool for complex constants.
     Register DstReg = MI.getOperand(0).getReg();

llvm/lib/Target/RISCV/RISCVGISel.td

@@ -133,64 +133,10 @@ def : LdPat<extloadi16, LH, i32>;
 def : StPat<truncstorei8, SB, GPR, i32>;
 def : StPat<truncstorei16, SH, GPR, i32>;
 
-def : Pat<(sext (i32 GPR:$src)), (ADDIW GPR:$src, 0)>;
-
 def : Pat<(sext_inreg (i64 (add GPR:$rs1, simm12_lo:$imm)), i32),
           (ADDIW GPR:$rs1, simm12_lo:$imm)>;
 }
 
-let Predicates = [IsRV64, NoStdExtZba] in
-def : Pat<(zext (i32 GPR:$src)), (SRLI (i64 (SLLI GPR:$src, 32)), 32)>;
-
-let Predicates = [IsRV32, NoStdExtZbb, NoStdExtZbkb] in 
-def : Pat<(XLenVT (zext (i16 GPR:$src))),
-          (SRLI (XLenVT (SLLI GPR:$src, 16)), 16)>;
-
-let Predicates = [IsRV64, NoStdExtZbb, NoStdExtZbkb] in {
-def : Pat<(i64 (zext (i16 GPR:$src))),
-          (SRLI (XLenVT (SLLI GPR:$src, 48)), 48)>;
-def : Pat<(i32 (zext (i16 GPR:$src))),
-          (SRLI (XLenVT (SLLI GPR:$src, 48)), 48)>;
-}
-
-let Predicates = [IsRV32, NoStdExtZbb] in
-def : Pat<(XLenVT (sext (i16 GPR:$src))),
-          (SRAI (XLenVT (SLLI GPR:$src, 16)), 16)>;
-
-let Predicates = [IsRV64, NoStdExtZbb] in {
-def : Pat<(i64 (sext (i16 GPR:$src))),
-          (SRAI (XLenVT (SLLI GPR:$src, 48)), 48)>;
-def : Pat<(i32 (sext (i16 GPR:$src))),
-          (SRAI (XLenVT (SLLI GPR:$src, 48)), 48)>;
-}
-
-//===----------------------------------------------------------------------===//
-// Zb* RV64 patterns not used by SelectionDAG.
-//===----------------------------------------------------------------------===//
-
-let Predicates = [HasStdExtZba, IsRV64] in {
-def : Pat<(zext (i32 GPR:$src)), (ADD_UW GPR:$src, (XLenVT X0))>;
-}
-
-let Predicates = [HasStdExtZbb] in
-def : Pat<(i32 (sext (i16 GPR:$rs))), (SEXT_H GPR:$rs)>;
-let Predicates = [HasStdExtZbb, IsRV64] in
-def : Pat<(i64 (sext (i16 GPR:$rs))), (SEXT_H GPR:$rs)>;
-
-let Predicates = [HasStdExtZbb, IsRV32] in
-def : Pat<(i32 (zext (i16 GPR:$rs))), (ZEXT_H_RV32 GPR:$rs)>;
-let Predicates = [HasStdExtZbb, IsRV64] in {
-def : Pat<(i64 (zext (i16 GPR:$rs))), (ZEXT_H_RV64 GPR:$rs)>;
-def : Pat<(i32 (zext (i16 GPR:$rs))), (ZEXT_H_RV64 GPR:$rs)>;
-}
-
-let Predicates = [HasStdExtZbkb, NoStdExtZbb, IsRV32] in
-def : Pat<(i32 (zext (i16 GPR:$rs))), (PACK GPR:$rs, (XLenVT X0))>;
-let Predicates = [HasStdExtZbkb, NoStdExtZbb, IsRV64] in {
-def : Pat<(i64 (zext (i16 GPR:$rs))), (PACKW GPR:$rs, (XLenVT X0))>;
-def : Pat<(i32 (zext (i16 GPR:$rs))), (PACKW GPR:$rs, (XLenVT X0))>;
-}
-
 //===----------------------------------------------------------------------===//
 // Zalasr patterns not used by SelectionDAG
 //===----------------------------------------------------------------------===//