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

[Thorsten Schütt via llvm-commits]

================
@@ -1984,3 +1984,323 @@ Type *llvm::getTypeForLLT(LLT Ty, LLVMContext &C) {
                            Ty.getElementCount());
   return IntegerType::get(C, Ty.getSizeInBits());
 }
+
+APInt llvm::GIConstant::getScalarValue() const {
+  assert(Kind == GIConstantKind::Scalar && "Expected scalar constant");
+
+  return Value;
+}
+
+std::optional<GIConstant>
+llvm::GIConstant::getConstant(Register Const, const MachineRegisterInfo &MRI) {
+  MachineInstr *Constant = getDefIgnoringCopies(Const, MRI);
+
+  if (GSplatVector *Splat = dyn_cast<GSplatVector>(Constant)) {
+    std::optional<ValueAndVReg> MayBeConstant =
+        getIConstantVRegValWithLookThrough(Splat->getValueReg(), MRI);
+    if (!MayBeConstant)
+      return std::nullopt;
+    return GIConstant(MayBeConstant->Value, GIConstantKind::ScalableVector);
+  }
+
+  if (GBuildVector *Build = dyn_cast<GBuildVector>(Constant)) {
+    SmallVector<APInt> Values;
+    unsigned NumSources = Build->getNumSources();
+    for (unsigned I = 0; I < NumSources; ++I) {
+      Register SrcReg = Build->getSourceReg(I);
+      std::optional<ValueAndVReg> MayBeConstant =
+          getIConstantVRegValWithLookThrough(SrcReg, MRI);
+      if (!MayBeConstant)
+        return std::nullopt;
+      Values.push_back(MayBeConstant->Value);
+    }
+    return GIConstant(Values);
+  }
+
+  std::optional<ValueAndVReg> MayBeConstant =
+      getIConstantVRegValWithLookThrough(Const, MRI);
+  if (!MayBeConstant)
+    return std::nullopt;
+
+  return GIConstant(MayBeConstant->Value, GIConstantKind::Scalar);
+}
+
+static bool isKnownNonZero(Register Reg, const MachineRegisterInfo &MRI,
+                           GISelKnownBits *KB, unsigned Depth);
+
+bool llvm::isKnownNonZero(Register Reg, const MachineRegisterInfo &MRI,
+                          GISelKnownBits *KB, unsigned Depth) {
+  if (!Reg.isVirtual())
+    return false;
+
+  LLT Ty = MRI.getType(Reg);
+  if (!Ty.isValid())
+    return false;
+
+  if (Ty.isPointer())
+    return false;
+
+  assert(Ty.isScalar() && "Expected a scalar value");
+  return ::isKnownNonZero(Reg, MRI, KB, Depth);
+}
+
+static bool matchOpWithOpEqZero(Register Op0, Register Op1,
+                                const MachineRegisterInfo &MRI) {
+  MachineInstr *MI = MRI.getVRegDef(Op0);
+
+  bool Result = false;
+
+  if (GZextOrSextOp *ZS = dyn_cast<GZextOrSextOp>(MI)) {
+    MachineInstr *SrcMI = MRI.getVRegDef(ZS->getSrcReg());
+    if (GICmp *Cmp = dyn_cast<GICmp>(SrcMI)) {
+      std::optional<ValueAndVReg> MayBeConstant =
+          getIConstantVRegValWithLookThrough(Cmp->getRHSReg(), MRI);
+      if (MayBeConstant)
+        Result |= (MayBeConstant->Value == 0) && (Cmp->getLHSReg() == Op1) &&
+                  (Cmp->getCond() == ICmpInst::ICMP_EQ);
+    }
+  }
+
+  MI = MRI.getVRegDef(Op1);
+  if (GZextOrSextOp *ZS = dyn_cast<GZextOrSextOp>(MI)) {
+    MachineInstr *SrcMI = MRI.getVRegDef(ZS->getSrcReg());
+    if (GICmp *Cmp = dyn_cast<GICmp>(SrcMI)) {
+      std::optional<ValueAndVReg> MayBeConstant =
+          getIConstantVRegValWithLookThrough(Cmp->getRHSReg(), MRI);
+      if (MayBeConstant)
+        Result |= (MayBeConstant->Value == 0) && (Cmp->getLHSReg() == Op0) &&
+                  (Cmp->getCond() == ICmpInst::ICMP_EQ);
+    }
+  }
----------------
tschuett wrote:

Copy-and-paste:
https://github.com/llvm/llvm-project/blob/dff3c9614144012afc51e0d5455512e4974c6ced/llvm/lib/Analysis/ValueTracking.cpp#L2590

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