[ValueTracking] Add logic for isKnownNonZero(umin X, Y)

`(umin X, Y) != 0` -> `X != 0 && Y != 0`

Alive2 Link:
    https://alive2.llvm.org/ce/z/AQh67i

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D149416

Author: goldsteinn

llvm/lib/Analysis/ValueTracking.cpp

@@ -2942,6 +2942,9 @@ bool isKnownNonZero(const Value *V, const APInt &DemandedElts, unsigned Depth,
             isKnownNonZero(II->getArgOperand(1), DemandedElts, Depth, Q))
           return true;
         break;
+      case Intrinsic::umin:
+        return isKnownNonZero(II->getArgOperand(0), DemandedElts, Depth, Q) &&
+               isKnownNonZero(II->getArgOperand(1), DemandedElts, Depth, Q);
       case Intrinsic::cttz:
         return computeKnownBits(II->getArgOperand(0), DemandedElts, Depth, Q)
             .Zero[0];

llvm/test/Analysis/ValueTracking/known-non-zero.ll

@@ -994,10 +994,7 @@ define i1 @umin_nonzero(i8 %xx, i8 %yy, i8 %ind) {
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[X_NZ]])
 ; CHECK-NEXT:    [[Y_NZ:%.*]] = icmp ne i8 [[YY:%.*]], 0
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[Y_NZ]])
-; CHECK-NEXT:    [[X:%.*]] = call i8 @llvm.umin.i8(i8 [[XX]], i8 [[YY]])
-; CHECK-NEXT:    [[Z:%.*]] = or i8 [[X]], [[IND:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[Z]], 0
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 false
 ;
   %x_nz = icmp ne i8 %xx, 0
   call void @llvm.assume(i1 %x_nz)
@@ -1032,10 +1029,7 @@ define i1 @smin_nonzero(i8 %xx, i8 %yy, i8 %ind) {
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[X_NZ]])
 ; CHECK-NEXT:    [[Y_NZ:%.*]] = icmp ne i8 [[YY:%.*]], 0
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[Y_NZ]])
-; CHECK-NEXT:    [[X:%.*]] = call i8 @llvm.umin.i8(i8 [[XX]], i8 [[YY]])
-; CHECK-NEXT:    [[Z:%.*]] = or i8 [[X]], [[IND:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[Z]], 0
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 false
 ;
   %x_nz = icmp ne i8 %xx, 0
   call void @llvm.assume(i1 %x_nz)