[RISCV] Support P extension ABSW instruction. (llvm#165047)

Author: topperc

llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp

@@ -3995,6 +3995,7 @@ bool RISCVDAGToDAGISel::hasAllNBitUsers(SDNode *Node, unsigned Bits,
     case RISCV::CTZW:
     case RISCV::CPOPW:
     case RISCV::SLLI_UW:
+    case RISCV::ABSW:
     case RISCV::FMV_W_X:
     case RISCV::FCVT_H_W:
     case RISCV::FCVT_H_W_INX:

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -433,6 +433,8 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
   if (Subtarget.hasStdExtP() ||
       (Subtarget.hasVendorXCValu() && !Subtarget.is64Bit())) {
     setOperationAction(ISD::ABS, XLenVT, Legal);
+    if (Subtarget.is64Bit())
+      setOperationAction(ISD::ABS, MVT::i32, Custom);
   } else if (Subtarget.hasShortForwardBranchOpt()) {
     // We can use PseudoCCSUB to implement ABS.
     setOperationAction(ISD::ABS, XLenVT, Legal);
@@ -14816,8 +14818,16 @@ void RISCVTargetLowering::ReplaceNodeResults(SDNode *N,
     assert(N->getValueType(0) == MVT::i32 && Subtarget.is64Bit() &&
            "Unexpected custom legalisation");
 
+    if (Subtarget.hasStdExtP()) {
+      SDValue Src =
+          DAG.getNode(ISD::ANY_EXTEND, DL, MVT::i64, N->getOperand(0));
+      SDValue Abs = DAG.getNode(RISCVISD::ABSW, DL, MVT::i64, Src);
+      Results.push_back(DAG.getNode(ISD::TRUNCATE, DL, MVT::i32, Abs));
+      return;
+    }
+
     if (Subtarget.hasStdExtZbb()) {
-      // Emit a special ABSW node that will be expanded to NEGW+MAX at isel.
+      // Emit a special node that will be expanded to NEGW+MAX at isel.
       // This allows us to remember that the result is sign extended. Expanding
       // to NEGW+MAX here requires a Freeze which breaks ComputeNumSignBits.
       SDValue Src = DAG.getNode(ISD::SIGN_EXTEND, DL, MVT::i64,
@@ -20290,6 +20300,7 @@ SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
 
     break;
   }
+  case RISCVISD::ABSW:
   case RISCVISD::CLZW:
   case RISCVISD::CTZW: {
     // Only the lower 32 bits of the first operand are read
@@ -21862,6 +21873,7 @@ unsigned RISCVTargetLowering::ComputeNumSignBitsForTargetNode(
   case RISCVISD::REMUW:
   case RISCVISD::ROLW:
   case RISCVISD::RORW:
+  case RISCVISD::ABSW:
   case RISCVISD::FCVT_W_RV64:
   case RISCVISD::FCVT_WU_RV64:
   case RISCVISD::STRICT_FCVT_W_RV64:

llvm/lib/Target/RISCV/RISCVInstrInfoP.td

@@ -1461,5 +1461,10 @@ let Predicates = [HasStdExtP, IsRV32] in {
 // Codegen patterns
 //===----------------------------------------------------------------------===//
 
+def riscv_absw : RVSDNode<"ABSW", SDTIntUnaryOp>;
+
 let Predicates = [HasStdExtP] in
 def : PatGpr<abs, ABS>;
+
+let Predicates = [HasStdExtP, IsRV64] in
+def : PatGpr<riscv_absw, ABSW>;

llvm/lib/Target/RISCV/RISCVOptWInstrs.cpp

@@ -172,6 +172,7 @@ static bool hasAllNBitUsers(const MachineInstr &OrigMI,
       case RISCV::CTZW:
       case RISCV::CPOPW:
       case RISCV::SLLI_UW:
+      case RISCV::ABSW:
       case RISCV::FMV_W_X:
       case RISCV::FCVT_H_W:
       case RISCV::FCVT_H_W_INX:

llvm/test/CodeGen/RISCV/rv64p.ll

@@ -297,8 +297,7 @@ declare i32 @llvm.abs.i32(i32, i1 immarg)
 define i32 @abs_i32(i32 %x) {
 ; CHECK-LABEL: abs_i32:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    sext.w a0, a0
-; CHECK-NEXT:    abs a0, a0
+; CHECK-NEXT:    absw a0, a0
 ; CHECK-NEXT:    ret
   %abs = tail call i32 @llvm.abs.i32(i32 %x, i1 true)
   ret i32 %abs
@@ -307,8 +306,7 @@ define i32 @abs_i32(i32 %x) {
 define signext i32 @abs_i32_sext(i32 signext %x) {
 ; CHECK-LABEL: abs_i32_sext:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    abs a0, a0
-; CHECK-NEXT:    sext.w a0, a0
+; CHECK-NEXT:    absw a0, a0
 ; CHECK-NEXT:    ret
   %abs = tail call i32 @llvm.abs.i32(i32 %x, i1 true)
   ret i32 %abs