1 files changed, 31 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 8b3d16a5125..b4473f857e2 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1523,6 +1523,37 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
             Known2.One.shl(ShiftAmt) | Known3.One.lshr(BitWidth - ShiftAmt);
         break;
       }
+      case Intrinsic::uadd_sat:
+      case Intrinsic::usub_sat: {
+        bool IsAdd = II->getIntrinsicID() == Intrinsic::uadd_sat;
+        computeKnownBits(I->getOperand(0), Known, Depth + 1, Q);
+        computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);
+
+        // Add: Leading ones of either operand are preserved.
+        // Sub: Leading zeros of LHS and leading ones of RHS are preserved
+        // as leading zeros in the result.
+        unsigned LeadingKnown;
+        if (IsAdd)
+          LeadingKnown = std::max(Known.countMinLeadingOnes(),
+                                  Known2.countMinLeadingOnes());
+        else
+          LeadingKnown = std::max(Known.countMinLeadingZeros(),
+                                  Known2.countMinLeadingOnes());
+
+        Known = KnownBits::computeForAddSub(
+            IsAdd, /* NSW */ false, Known, Known2);
+
+        // We select between the operation result and all-ones/zero
+        // respectively, so we can preserve known ones/zeros.
+        if (IsAdd) {
+          Known.One.setHighBits(LeadingKnown);
+          Known.Zero.clearAllBits();
+        } else {
+          Known.Zero.setHighBits(LeadingKnown);
+          Known.One.clearAllBits();
+        }
+        break;
+      }
       case Intrinsic::x86_sse42_crc32_64_64:
         Known.Zero.setBitsFrom(32);
         break;