[PowerPC] Combine ADD to ADDZE

[HLJ2009]

Summary

On the ppc64le platform, I found that if ir has the following form,

define i64 @addze1(i64 %x, i64 %z) local_unnamed_addr #0 {
entry:
  %cmp = icmp ne i64 %z, CONSTANT      (-32767 <= CONSTANT <= 32768)
  %conv1 = zext i1 %cmp to i64
  %add = add nsw i64 %conv1, %x
  ret i64 %add
}

we can optimize it to the form below.

                                when C == 0
                            --> addze X, (addic Z, -1))
                           /
add X, (zext(setne Z, C))--
                           \    when -32768 <= -C <= 32767 && C != 0
                            --> addze X, (addic (addi Z, -C), -1)

Besides , if ir has the following form,

define i64 @addze2(i64 %x, i64 %z) local_unnamed_addr #0 {
entry:
  %cmp = icmp eq i64 %z, CONSTANT      (-32767 <= CONSTANT <= 32768)
  %conv1 = zext i1 %cmp to i64
  %add = add nsw i64 %conv1, %x
  ret i64 %add
}

we can optimize it to the form below.

                                when C == 0
                            --> addze X, (subfic Z, 0)
                           /
add X, (zext(setne Z, C))--
                           \    when -32768 <= -C <= 32767 && C != 0
                            --> addze X, (subfic (addi Z, -C), 0)

[inouehrs]

Does this code pattern frequently happen?

[HLJ2009]

In D51403#1217066, @inouehrs wrote:

Does this code pattern frequently happen?

This code does not necessarily be executed frequently, but I think this is also a point that can be optimized.

[nemanjai]

LGTM aside from a minor nit which you can fix on the commit.

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

14177

I think it might be clearer if you show that it is only the carry from the addic that is being used in the addze (since addze only takes one explicit operand). Perhaps something like:
addze X, (addic Z, -1).1 or addze X, (addic Z, -1).carry

[HLJ2009]

Modify comments using nemanjai's suggestion

[HLJ2009]

Limit optimization platforms to ppc64 and ppc64le

[HLJ2009]

Hi Steven @steven.zhang. I don't have the commit access. Could you help to commit the change for me? Thanks.

llvm/lib/Target/PowerPC/PPCISelLowering.h

private:
     SDValue DAGCombineExtBoolTrunc(SDNode *N, DAGCombinerInfo &DCI) const;
     SDValue DAGCombineBuildVector(SDNode *N, DAGCombinerInfo &DCI) const;
     SDValue DAGCombineTruncBoolExt(SDNode *N, DAGCombinerInfo &DCI) const;
     SDValue combineStoreFPToInt(SDNode *N, DAGCombinerInfo &DCI) const;
     SDValue combineFPToIntToFP(SDNode *N, DAGCombinerInfo &DCI) const;
     SDValue combineSHL(SDNode *N, DAGCombinerInfo &DCI) const;
     SDValue combineSRA(SDNode *N, DAGCombinerInfo &DCI) const;
     SDValue combineSRL(SDNode *N, DAGCombinerInfo &DCI) const;
+    SDValue combineADD(SDNode *N, DAGCombinerInfo &DCI) const;
 
     /// ConvertSETCCToSubtract - looks at SETCC that compares ints. It replaces
     /// SETCC with integer subtraction when (1) there is a legal way of doing it
     /// (2) keeping the result of comparison in GPR has performance benefit.
     SDValue ConvertSETCCToSubtract(SDNode *N, DAGCombinerInfo &DCI) const;
 
     SDValue getSqrtEstimate(SDValue Operand, SelectionDAG &DAG, int Enabled,
                             int &RefinementSteps, bool &UseOneConstNR,

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

if (!isPPC64) {
     setLibcallName(RTLIB::SHL_I128, nullptr);
     setLibcallName(RTLIB::SRL_I128, nullptr);
     setLibcallName(RTLIB::SRA_I128, nullptr);
   }
 
   setStackPointerRegisterToSaveRestore(isPPC64 ? PPC::X1 : PPC::R1);
 
   // We have target-specific dag combine patterns for the following nodes:
+  setTargetDAGCombine(ISD::ADD);
   setTargetDAGCombine(ISD::SHL);
   setTargetDAGCombine(ISD::SRA);
   setTargetDAGCombine(ISD::SRL);
   setTargetDAGCombine(ISD::SINT_TO_FP);
   setTargetDAGCombine(ISD::BUILD_VECTOR);
   if (Subtarget.hasFPCVT())
     setTargetDAGCombine(ISD::UINT_TO_FP);
   setTargetDAGCombine(ISD::LOAD);

 }
 
 SDValue PPCTargetLowering::PerformDAGCombine(SDNode *N,
                                              DAGCombinerInfo &DCI) const {
   SelectionDAG &DAG = DCI.DAG;
   SDLoc dl(N);
   switch (N->getOpcode()) {
   default: break;
+  case ISD::ADD:
+    return combineADD(N, DCI);
   case ISD::SHL:
     return combineSHL(N, DCI);
   case ISD::SRA:
     return combineSRA(N, DCI);
   case ISD::SRL:
     return combineSRL(N, DCI);
   case PPCISD::SHL:
     if (isNullConstant(N->getOperand(0))) // 0 << V -> 0.

 
 SDValue PPCTargetLowering::combineSRL(SDNode *N, DAGCombinerInfo &DCI) const {
   if (auto Value = stripModuloOnShift(*this, N, DCI.DAG))
     return Value;
 
   return SDValue();
 }
 
+// Transform (add X, (zext(setne Z, C))) -> (addze X, (addic (addi Z, -C), -1))
+// Transform (add X, (zext(sete  Z, C))) -> (addze X, (subfic (addi Z, -C), 0))
+// When C is zero, the equation (addi Z, -C) can be simplified to Z
+// Requirement: -C in [-32768, 32767], X and Z are MVT::i64 types
+static SDValue combineADDToADDZE(SDNode *N, SelectionDAG &DAG) {
+  SDValue LHS = N->getOperand(0);
+  SDValue RHS = N->getOperand(1);
+
+  auto isZextOfCompareWithConstant = [](SDValue Op) {
+    if (Op.getOpcode() != ISD::ZERO_EXTEND || !Op.hasOneUse() ||
+        Op.getValueType() != MVT::i64)
+      return false;
+
+    SDValue Cmp = Op.getOperand(0);
+    if (Cmp.getOpcode() != ISD::SETCC || !Cmp.hasOneUse() ||
+        Cmp.getOperand(0).getValueType() != MVT::i64)
+      return false;
+
+    if (auto *Constant = dyn_cast<ConstantSDNode>(Cmp.getOperand(1))) {
+      int64_t NegConstant = 0 - Constant->getSExtValue();
+      // Due to the limitations of the addi instruction,
+      // -C is required to be [-32768, 32767].
+      return isInt<16>(NegConstant);
+    }
+
+    return false;
+  };
+
+  bool LHSHasPattern = isZextOfCompareWithConstant(LHS);
+  bool RHSHasPattern = isZextOfCompareWithConstant(RHS);
+
+  // If there is a pattern, canonicalize a zext operand to the RHS.
+  if (LHSHasPattern && !RHSHasPattern)
+    std::swap(LHS, RHS);
+  else if (!LHSHasPattern && !RHSHasPattern)
+    return SDValue();
+
+  SDLoc DL(N);
+  SDVTList VTs = DAG.getVTList(MVT::i64, MVT::i64);
+  SDValue Cmp = RHS.getOperand(0);
+  SDValue Z = Cmp.getOperand(0);
+  auto *Constant = dyn_cast<ConstantSDNode>(Cmp.getOperand(1));
+
+  assert(Constant && "Constant Should not be a null pointer.");
+  int64_t NegConstant = 0 - Constant->getSExtValue();
+
+  switch(cast<CondCodeSDNode>(Cmp.getOperand(2))->get()) {
+  default: break;
+  case ISD::SETNE: {
+    //                                 when C == 0
+    //                             --> addze X, (addic Z, -1))
+    //                            /
+    // add X, (zext(setne Z, C))--
+    //                            \    when -32768 <= -C <= 32767 && C != 0
+    //                             --> addze X, (addic (addi Z, -C), -1)
+    SDValue Add = DAG.getNode(ISD::ADD, DL, MVT::i64, Z,
+                              DAG.getConstant(NegConstant, DL, MVT::i64));
+    SDValue AddOrZ = NegConstant != 0 ? Add : Z;
+    SDValue Addc = DAG.getNode(ISD::ADDC, DL, DAG.getVTList(MVT::i64, MVT::Glue),
+                               AddOrZ, DAG.getConstant(-1ULL, DL, MVT::i64));
+    return DAG.getNode(ISD::ADDE, DL, VTs, LHS, DAG.getConstant(0, DL, MVT::i64),
+                       SDValue(Addc.getNode(), 1));
+    }
+  case ISD::SETEQ: {
+    //                                 when C == 0
+    //                             --> addze X, (subfic Z, 0)
+    //                            /
+    // add X, (zext(sete  Z, C))--
+    //                            \    when -32768 <= -C <= 32767 && C != 0
+    //                             --> addze X, (subfic (addi Z, -C), 0)
+    SDValue Add = DAG.getNode(ISD::ADD, DL, MVT::i64, Z,
+                              DAG.getConstant(NegConstant, DL, MVT::i64));
+    SDValue AddOrZ = NegConstant != 0 ? Add : Z;
+    SDValue Subc = DAG.getNode(ISD::SUBC, DL, DAG.getVTList(MVT::i64, MVT::Glue),
+                               DAG.getConstant(0, DL, MVT::i64), AddOrZ);
+    return DAG.getNode(ISD::ADDE, DL, VTs, LHS, DAG.getConstant(0, DL, MVT::i64),
+                       SDValue(Subc.getNode(), 1));
+    }
+  }
+
+  return SDValue();
+}
+
+SDValue PPCTargetLowering::combineADD(SDNode *N, DAGCombinerInfo &DCI) const {
+  if (auto Value = combineADDToADDZE(N, DCI.DAG))
+    return Value;
+
+  return SDValue();
+}
+
 bool PPCTargetLowering::mayBeEmittedAsTailCall(const CallInst *CI) const {
   // Only duplicate to increase tail-calls for the 64bit SysV ABIs.
   if (!Subtarget.isSVR4ABI() || !Subtarget.isPPC64())
     return false;
 
   // If not a tail call then no need to proceed.
   if (!CI->isTailCall())
     return false;

llvm/test/CodeGen/PowerPC/addze.ll

+; RUN: llc -verify-machineinstrs -mtriple=powerpc64-unknown-unknown \
+; RUN:  -ppc-asm-full-reg-names -mcpu=pwr9 < %s  | FileCheck %s
+; RUN: llc -verify-machineinstrs -mtriple=powerpc64le-unknown-unknown \
+; RUN:  -ppc-asm-full-reg-names -mcpu=pwr9 < %s  | FileCheck %s
+
+define i64 @addze1(i64 %X, i64 %Z) {
+; CHECK-LABEL: addze1:
+; CHECK: # %bb.0:
+; CHECK-NEXT: addic [[REG1:r[0-9]+]], [[REG1]], -1
+; CHECK-NEXT: addze [[REG2:r[0-9]+]], [[REG2]]
+; CHECK-NEXT: blr
+  %cmp = icmp ne i64 %Z, 0
+  %conv1 = zext i1 %cmp to i64
+  %add = add nsw i64 %conv1, %X
+  ret i64 %add
+}
+
+define i64 @addze2(i64 %X, i64 %Z) {
+; CHECK-LABEL: addze2:
+; CHECK: # %bb.0:
+; CHECK-NEXT: subfic [[REG1:r[0-9]+]], [[REG1]], 0
+; CHECK-NEXT: addze  [[REG2:r[0-9]+]], [[REG2]]
+; CHECK-NEXT: blr
+  %cmp = icmp eq i64 %Z, 0
+  %conv1 = zext i1 %cmp to i64
+  %add = add nsw i64 %conv1, %X
+  ret i64 %add
+}
+
+define i64 @addze3(i64 %X, i64 %Z) {
+; CHECK-LABEL: addze3:
+; CHECK: # %bb.0:
+; CHECK-NEXT: addi  [[REG1:r[0-9]+]], [[REG1]], -32768
+; CHECK-NEXT: addic [[REG1]], [[REG1]], -1
+; CHECK-NEXT: addze [[REG2:r[0-9]+]], [[REG2]]
+; CHECK-NEXT: blr
+  %cmp = icmp ne i64 %Z, 32768
+  %conv1 = zext i1 %cmp to i64
+  %add = add nsw i64 %conv1, %X
+  ret i64 %add
+}
+
+define i64 @addze4(i64 %X, i64 %Z) {
+; CHECK-LABEL: addze4:
+; CHECK: # %bb.0:
+; CHECK-NEXT: addi   [[REG1:r[0-9]+]], [[REG1]], -32768
+; CHECK-NEXT: subfic [[REG1]], [[REG1]], 0
+; CHECK-NEXT: addze  [[REG2:r[0-9]+]], [[REG2]]
+; CHECK-NEXT: blr
+  %cmp = icmp eq i64 %Z, 32768
+  %conv1 = zext i1 %cmp to i64
+  %add = add nsw i64 %conv1, %X
+  ret i64 %add
+}
+
+define i64 @addze5(i64 %X, i64 %Z) {
+; CHECK-LABEL: addze5:
+; CHECK: # %bb.0:
+; CHECK-NEXT: addi  [[REG1:r[0-9]+]], [[REG1]], 32767
+; CHECK-NEXT: addic [[REG1]], [[REG1]], -1
+; CHECK-NEXT: addze [[REG2:r[0-9]+]], [[REG2]]
+; CHECK-NEXT: blr
+  %cmp = icmp ne i64 %Z, -32767
+  %conv1 = zext i1 %cmp to i64
+  %add = add nsw i64 %conv1, %X
+  ret i64 %add
+}
+
+define i64 @addze6(i64 %X, i64 %Z) {
+; CHECK-LABEL: addze6:
+; CHECK: # %bb.0:
+; CHECK-NEXT: addi   [[REG1:r[0-9]+]], [[REG1]], 32767
+; CHECK-NEXT: subfic [[REG1]], [[REG1]], 0
+; CHECK-NEXT: addze  [[REG2:r[0-9]+]], [[REG2]]
+; CHECK-NEXT: blr
+  %cmp = icmp eq i64 %Z, -32767
+  %conv1 = zext i1 %cmp to i64
+  %add = add nsw i64 %conv1, %X
+  ret i64 %add
+}
+
+; element is out of range
+define i64 @test1(i64 %X, i64 %Z) {
+; CHECK-LABEL: test1:
+; CHECK: # %bb.0:
+; CHECK-NEXT: li    [[REG1:r[0-9]+]], -32768
+; CHECK-NEXT: xor   [[REG2:r[0-9]+]], [[REG2]], [[REG1]]
+; CHECK-NEXT: addic [[REG1]], [[REG2]], -1
+; CHECK-NEXT: subfe [[REG2]], [[REG1]], [[REG2]]
+; CHECK-NEXT: add   [[REG3:r[0-9]+]], [[REG2]], [[REG3]]
+; CHECK-NEXT: blr
+  %cmp = icmp ne i64 %Z, -32768
+  %conv1 = zext i1 %cmp to i64
+  %add = add nsw i64 %conv1, %X
+  ret i64 %add
+}
+
+define i64 @test2(i64 %X, i64 %Z) {
+; CHECK-LABEL: test2:
+; CHECK: # %bb.0:
+; CHECK-NEXT: li     [[REG1:r[0-9]+]], -32768
+; CHECK-NEXT: xor    [[REG2:r[0-9]+]], [[REG2]], [[REG1]]
+; CHECK-NEXT: cntlzd [[REG2]], [[REG2]]
+; CHECK-NEXT: rldicl [[REG2]], [[REG2]], 58, 63
+; CHECK-NEXT: add    [[REG3:r[0-9]+]], [[REG2]], [[REG3]]
+; CHECK-NEXT: blr
+  %cmp = icmp eq i64 %Z, -32768
+  %conv1 = zext i1 %cmp to i64
+  %add = add nsw i64 %conv1, %X
+  ret i64 %add
+}
+
+define i64 @test3(i64 %X, i64 %Z) {
+; CHECK-LABEL: test3:
+; CHECK: # %bb.0:
+; CHECK-NEXT: li    [[REG1:r[0-9]+]], 0
+; CHECK-NEXT: ori   [[REG1]], [[REG1]], 32769
+; CHECK-NEXT: xor   [[REG2:r[0-9]+]], [[REG2]], [[REG1]]
+; CHECK-NEXT: addic [[REG1]], [[REG2]], -1
+; CHECK-NEXT: subfe [[REG2]], [[REG1]], [[REG2]]
+; CHECK-NEXT: add   [[REG3:r[0-9]+]], [[REG2]], [[REG3]]
+; CHECK-NEXT: blr
+  %cmp = icmp ne i64 %Z, 32769
+  %conv1 = zext i1 %cmp to i64
+  %add = add nsw i64 %conv1, %X
+  ret i64 %add
+}
+
+define i64 @test4(i64 %X, i64 %Z) {
+; CHECK-LABEL: test4:
+; CHECK: # %bb.0:
+; CHECK-NEXT: li     [[REG1:r[0-9]+]], 0
+; CHECK-NEXT: ori    [[REG1]], [[REG1]], 32769
+; CHECK-NEXT: xor    [[REG2:r[0-9]+]], [[REG2]], [[REG1]]
+; CHECK-NEXT: cntlzd [[REG2]], [[REG2]]
+; CHECK-NEXT: rldicl [[REG2]], [[REG2]], 58, 63
+; CHECK-NEXT: add    [[REG3:r[0-9]+]], [[REG2]], [[REG3]]
+; CHECK-NEXT: blr
+  %cmp = icmp eq i64 %Z, 32769
+  %conv1 = zext i1 %cmp to i64
+  %add = add nsw i64 %conv1, %X
+  ret i64 %add
+}
+
+; comparison of two registers
+define i64 @test5(i64 %X, i64 %Y, i64 %Z) {
+; CHECK-LABEL: test5:
+; CHECK: # %bb.0:
+; CHECK-NEXT: xor   [[REG2:r[0-9]+]], [[REG2]], [[REG1:r[0-9]+]]
+; CHECK-NEXT: addic [[REG1]], [[REG2]], -1
+; CHECK-NEXT: subfe [[REG2]], [[REG1]], [[REG2]]
+; CHECK-NEXT: add   [[REG3:r[0-9]+]], [[REG2]], [[REG3]]
+; CHECK-NEXT: blr
+  %cmp = icmp ne i64 %Y, %Z
+  %conv1 = zext i1 %cmp to i64
+  %add = add nsw i64 %conv1, %X
+  ret i64 %add
+}
+
+define i64 @test6(i64 %X, i64 %Y, i64 %Z) {
+; CHECK-LABEL: test6:
+; CHECK: # %bb.0:
+; CHECK-NEXT: xor    [[REG2:r[0-9]+]], [[REG2]], [[REG1:r[0-9]+]]
+; CHECK-NEXT: cntlzd [[REG2]], [[REG2]]
+; CHECK-NEXT: rldicl [[REG2]], [[REG2]], 58, 63
+; CHECK-NEXT: add    [[REG3:r[0-9]+]], [[REG2]], [[REG3]]
+; CHECK-NEXT: blr
+  %cmp = icmp eq i64 %Y, %Z
+  %conv1 = zext i1 %cmp to i64
+  %add = add nsw i64 %conv1, %X
+  ret i64 %add
+}