[llvm] [GlobalIsel] Combine logic of icmps (PR #77855)

[Thorsten Schütt via llvm-commits]

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@@ -6643,3 +6644,178 @@ bool CombinerHelper::matchSelect(MachineInstr &MI, BuildFnTy &MatchInfo) {
 
   return false;
 }
+
+/// Fold (icmp Pred1 V1, C1) && (icmp Pred2 V2, C2)
+/// or   (icmp Pred1 V1, C1) || (icmp Pred2 V2, C2)
+/// into a single comparison using range-based reasoning.
+/// see InstCombinerImpl::foldAndOrOfICmpsUsingRanges.
+bool CombinerHelper::tryFoldAndOrOrICmpsUsingRanges(GLogicalBinOp *Logic,
+                                                    BuildFnTy &MatchInfo) {
+  assert(Logic->getOpcode() != TargetOpcode::G_XOR && "unexpected xor");
+  bool IsAnd = Logic->getOpcode() == TargetOpcode::G_AND;
+  Register DstReg = Logic->getReg(0);
+  Register LHS = Logic->getLHSReg();
+  Register RHS = Logic->getRHSReg();
+  unsigned Flags = Logic->getFlags();
+
+  // We need an G_ICMP on the LHS register.
+  GICmp *Cmp1 = getOpcodeDef<GICmp>(LHS, MRI);
+  if (!Cmp1)
+    return false;
+
+  // We need an G_ICMP on the RHS register.
+  GICmp *Cmp2 = getOpcodeDef<GICmp>(RHS, MRI);
+  if (!Cmp2)
+    return false;
+
+  APInt C1;
+  APInt C2;
+  std::optional<ValueAndVReg> MaybeC1 =
+      getIConstantVRegValWithLookThrough(Cmp1->getRHSReg(), MRI);
+  if (!MaybeC1)
+    return false;
+  C1 = MaybeC1->Value;
+
+  std::optional<ValueAndVReg> MaybeC2 =
+      getIConstantVRegValWithLookThrough(Cmp2->getRHSReg(), MRI);
+  if (!MaybeC2)
+    return false;
+  C2 = MaybeC2->Value;
+
+  Register R1 = Cmp1->getLHSReg();
+  Register R2 = Cmp2->getLHSReg();
+  CmpInst::Predicate Pred1 = Cmp1->getCond();
+  CmpInst::Predicate Pred2 = Cmp2->getCond();
+  LLT CmpTy = MRI.getType(Cmp1->getReg(0));
+  LLT CmpOperandTy = MRI.getType(R1);
+
+  // We build ands, adds, and constants of type CmpOperandTy.
+  // They must be legal to build.
+  if (!isLegalOrBeforeLegalizer({TargetOpcode::G_AND, CmpOperandTy}) ||
+      !isLegalOrBeforeLegalizer({TargetOpcode::G_ADD, CmpOperandTy}) ||
+      !isLegalOrBeforeLegalizer({TargetOpcode::G_CONSTANT, CmpOperandTy}))
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tschuett wrote:

I did. The intent is more obvious, but this combine is only uses scalars.

https://github.com/llvm/llvm-project/pull/77855