"Recommit "[ConstraintElim] Simplify cmp after uadd.sat/usub.sat (#135603)"

Author: el-ev

llvm/lib/Transforms/Scalar/ConstraintElimination.cpp

@@ -1139,6 +1139,8 @@ void State::addInfoFor(BasicBlock &BB) {
       // when simplifying uses of the min/max intrinsics.
       [[fallthrough]];
     case Intrinsic::abs:
+    case Intrinsic::uadd_sat:
+    case Intrinsic::usub_sat:
       if (!isGuaranteedNotToBePoison(&I))
         break;
       WorkList.push_back(FactOrCheck::getInstFact(DT.getNode(&BB), &I));
@@ -1896,6 +1898,20 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT, LoopInfo &LI,
         AddFact(Pred, MinMax, MinMax->getRHS());
         continue;
       }
+      if (auto *USatI = dyn_cast<SaturatingInst>(CB.Inst)) {
+        switch (USatI->getIntrinsicID()) {
+        default:
+          llvm_unreachable("Unexpected intrinsic.");
+        case Intrinsic::uadd_sat:
+          AddFact(ICmpInst::ICMP_UGE, USatI, USatI->getLHS());
+          AddFact(ICmpInst::ICMP_UGE, USatI, USatI->getRHS());
+          break;
+        case Intrinsic::usub_sat:
+          AddFact(ICmpInst::ICMP_ULE, USatI, USatI->getLHS());
+          break;
+        }
+        continue;
+      }
     }
 
     Value *A = nullptr, *B = nullptr;

llvm/test/Transforms/ConstraintElimination/uadd-usub-sat.ll

@@ -8,9 +8,7 @@ define i1 @uadd_sat_uge(i64 noundef %a, i64 noundef %b) {
 ; CHECK-LABEL: define i1 @uadd_sat_uge(
 ; CHECK-SAME: i64 noundef [[A:%.*]], i64 noundef [[B:%.*]]) {
 ; CHECK-NEXT:    [[ADD_SAT:%.*]] = call i64 @llvm.uadd.sat.i64(i64 [[A]], i64 [[B]])
-; CHECK-NEXT:    [[CMP1:%.*]] = icmp uge i64 [[ADD_SAT]], [[A]]
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp uge i64 [[ADD_SAT]], [[B]]
-; CHECK-NEXT:    [[CMP:%.*]] = and i1 [[CMP1]], [[CMP2]]
+; CHECK-NEXT:    [[CMP:%.*]] = and i1 true, true
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %add.sat = call i64 @llvm.uadd.sat.i64(i64 %a, i64 %b)
@@ -24,8 +22,7 @@ define i1 @usub_sat_ule_lhs(i64 noundef %a, i64 noundef %b) {
 ; CHECK-LABEL: define i1 @usub_sat_ule_lhs(
 ; CHECK-SAME: i64 noundef [[A:%.*]], i64 noundef [[B:%.*]]) {
 ; CHECK-NEXT:    [[SUB_SAT:%.*]] = call i64 @llvm.usub.sat.i64(i64 [[A]], i64 [[B]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ule i64 [[SUB_SAT]], [[A]]
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %sub.sat = call i64 @llvm.usub.sat.i64(i64 %a, i64 %b)
   %cmp = icmp ule i64 %sub.sat, %a