[llvm] [InstCombine] Implement folds of icmp of UCMP/SCMP call and a constant (PR #96118)

[Dhruv Chawla via llvm-commits]

================
@@ -3926,6 +3926,92 @@ foldICmpUSubSatOrUAddSatWithConstant(ICmpInst::Predicate Pred,
       ConstantInt::get(Op1->getType(), EquivInt));
 }
 
+static Instruction *
+foldICmpOfCmpIntrinsicWithConstant(ICmpInst::Predicate Pred, IntrinsicInst *I,
+                                   const APInt &C,
+                                   InstCombiner::BuilderTy &Builder) {
+  Intrinsic::ID IID = I->getIntrinsicID();
+  Value *LHS = I->getOperand(0);
+  Value *RHS = I->getOperand(1);
+
+  switch (Pred) {
+  case ICmpInst::ICMP_EQ:
+    if (C.isZero())
+      return new ICmpInst(Pred, LHS, RHS);
+    if (C.isOne())
+      return new ICmpInst(IID == Intrinsic::scmp ? ICmpInst::ICMP_SGT
+                                                 : ICmpInst::ICMP_UGT,
+                          LHS, RHS);
+    if (C.isAllOnes())
+      return new ICmpInst(IID == Intrinsic::scmp ? ICmpInst::ICMP_SLT
+                                                 : ICmpInst::ICMP_ULT,
+                          LHS, RHS);
+    break;
+
+  case ICmpInst::ICMP_NE:
+    if (C.isZero())
+      return new ICmpInst(Pred, LHS, RHS);
+    if (C.isOne())
+      return new ICmpInst(IID == Intrinsic::scmp ? ICmpInst::ICMP_SLE
+                                                 : ICmpInst::ICMP_ULE,
+                          LHS, RHS);
+    if (C.isAllOnes())
+      return new ICmpInst(IID == Intrinsic::scmp ? ICmpInst::ICMP_SGE
+                                                 : ICmpInst::ICMP_UGE,
+                          LHS, RHS);
+    break;
+
+  case ICmpInst::ICMP_SGT:
+    if (C.isAllOnes())
+      return new ICmpInst(IID == Intrinsic::scmp ? ICmpInst::ICMP_SGE
+                                                 : ICmpInst::ICMP_UGE,
+                          LHS, RHS);
+    if (C.isZero())
+      return new ICmpInst(IID == Intrinsic::scmp ? ICmpInst::ICMP_SGT
+                                                 : ICmpInst::ICMP_UGT,
+                          LHS, RHS);
+    break;
+
+  case ICmpInst::ICMP_SGE:
+    if (C.isZero())
+      return new ICmpInst(IID == Intrinsic::scmp ? ICmpInst::ICMP_SGE
+                                                 : ICmpInst::ICMP_UGE,
+                          LHS, RHS);
+    if (C.isOne())
+      return new ICmpInst(IID == Intrinsic::scmp ? ICmpInst::ICMP_SGT
+                                                 : ICmpInst::ICMP_UGT,
+                          LHS, RHS);
+    break;
+
+  case ICmpInst::ICMP_SLT:
+    if (C.isZero())
+      return new ICmpInst(IID == Intrinsic::scmp ? ICmpInst::ICMP_SLT
+                                                 : ICmpInst::ICMP_ULT,
+                          LHS, RHS);
+    if (C.isOne())
+      return new ICmpInst(IID == Intrinsic::scmp ? ICmpInst::ICMP_SLE
+                                                 : ICmpInst::ICMP_ULE,
+                          LHS, RHS);
+    break;
+
+  case llvm::ICmpInst::ICMP_SLE:
----------------
dc03-work wrote:

Unnecessary `llvm::`

https://github.com/llvm/llvm-project/pull/96118