bypass poison check for usub.sat

Author: el-ev

llvm/lib/Transforms/Scalar/ConstraintElimination.cpp

@@ -1132,14 +1132,17 @@ void State::addInfoFor(BasicBlock &BB) {
     case Intrinsic::umax:
     case Intrinsic::smin:
     case Intrinsic::smax:
-    case Intrinsic::usub_sat:
       // TODO: handle llvm.abs as well
       WorkList.push_back(
           FactOrCheck::getCheck(DT.getNode(&BB), cast<CallInst>(&I)));
       // TODO: Check if it is possible to instead only added the min/max facts
       // when simplifying uses of the min/max intrinsics.
-      if (!isGuaranteedNotToBePoison(&I))
-        break;
+      if (isGuaranteedNotToBePoison(&I))
+        WorkList.push_back(FactOrCheck::getInstFact(DT.getNode(&BB), &I));
+      break;
+    case Intrinsic::usub_sat:
+      WorkList.push_back(
+          FactOrCheck::getCheck(DT.getNode(&BB), cast<CallInst>(&I)));
       [[fallthrough]];
     case Intrinsic::abs:
     case Intrinsic::uadd_sat:

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

@@ -8,7 +8,9 @@ define i1 @uadd_sat_uge(i64 %a, i64 %b) {
 ; CHECK-LABEL: define i1 @uadd_sat_uge(
 ; CHECK-SAME: i64 [[A:%.*]], i64 [[B:%.*]]) {
 ; CHECK-NEXT:    [[ADD_SAT:%.*]] = call i64 @llvm.uadd.sat.i64(i64 [[A]], i64 [[B]])
-; CHECK-NEXT:    [[CMP:%.*]] = and i1 true, true
+; 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:    ret i1 [[CMP]]
 ;
   %add.sat = call i64 @llvm.uadd.sat.i64(i64 %a, i64 %b)
@@ -35,7 +37,7 @@ define i64 @usub_sat_when_lhs_ugt_rhs(i64 %a, i64 %b) {
 ; CHECK-SAME: i64 [[A:%.*]], i64 [[B:%.*]]) {
 ; CHECK-NEXT:    [[PRECOND:%.*]] = icmp ugt i64 [[A]], [[B]]
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[PRECOND]])
-; CHECK-NEXT:    [[SUB_SAT:%.*]] = sub i64 [[A]], [[B]]
+; CHECK-NEXT:    [[SUB_SAT:%.*]] = call i64 @llvm.usub.sat.i64(i64 [[A]], i64 [[B]])
 ; CHECK-NEXT:    ret i64 [[SUB_SAT]]
 ;
   %precond = icmp ugt i64 %a, %b
@@ -49,7 +51,8 @@ define i64 @usub_sat_when_lhs_ule_rhs(i64 %a, i64 %b) {
 ; CHECK-SAME: i64 [[A:%.*]], i64 [[B:%.*]]) {
 ; CHECK-NEXT:    [[PRECOND:%.*]] = icmp ule i64 [[A]], [[B]]
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[PRECOND]])
-; CHECK-NEXT:    ret i64 0
+; CHECK-NEXT:    [[SUB_SAT:%.*]] = call i64 @llvm.usub.sat.i64(i64 [[A]], i64 [[B]])
+; CHECK-NEXT:    ret i64 [[SUB_SAT]]
 ;
   %precond = icmp ule i64 %a, %b
   call void @llvm.assume(i1 %precond)