[ValueTracking] Pass exact flag to KnownBits::udiv in `computeKno…

…wnBits`

This information was previously missing but we can use it for
determining the low-bits.

Differential Revision: https://reviews.llvm.org/D150095

llvm/lib/Analysis/ValueTracking.cpp

@@ -1208,7 +1208,8 @@ static void computeKnownBitsFromOperator(const Operator *I,
   case Instruction::UDiv: {
     computeKnownBits(I->getOperand(0), Known, Depth + 1, Q);
     computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);
-    Known = KnownBits::udiv(Known, Known2);
+    Known =
+        KnownBits::udiv(Known, Known2, Q.IIQ.isExact(cast<BinaryOperator>(I)));
     break;
   }
   case Instruction::Select: {

llvm/test/Analysis/ValueTracking/knownbits-div.ll

@@ -197,12 +197,7 @@ define i1 @udiv_high_bits(i8 %x, i8 %y) {
 
 define i1 @udiv_exact_odd_odd(i8 %x, i8 %y) {
 ; CHECK-LABEL: @udiv_exact_odd_odd(
-; CHECK-NEXT:    [[NUM:%.*]] = or i8 [[X:%.*]], 1
-; CHECK-NEXT:    [[DENUM:%.*]] = or i8 [[Y:%.*]], 1
-; CHECK-NEXT:    [[DIV:%.*]] = udiv exact i8 [[NUM]], [[DENUM]]
-; CHECK-NEXT:    [[AND:%.*]] = and i8 [[DIV]], 1
-; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[AND]], 0
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 false
 ;
   %num = or i8 %x, 1
   %denum = or i8 %y, 1
@@ -214,12 +209,7 @@ define i1 @udiv_exact_odd_odd(i8 %x, i8 %y) {
 
 define i1 @udiv_exact_even_odd(i8 %x, i8 %y) {
 ; CHECK-LABEL: @udiv_exact_even_odd(
-; CHECK-NEXT:    [[NUM:%.*]] = and i8 [[X:%.*]], -2
-; CHECK-NEXT:    [[DENUM:%.*]] = or i8 [[Y:%.*]], 1
-; CHECK-NEXT:    [[DIV:%.*]] = udiv exact i8 [[NUM]], [[DENUM]]
-; CHECK-NEXT:    [[AND:%.*]] = and i8 [[DIV]], 1
-; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[AND]], 1
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 false
 ;
   %num = and i8 %x, -2
   %denum = or i8 %y, 1