[InstCombine] allow commute in sub-of-umax fold

This fold was added with:
83c2fb9
...but missed the commuted pattern:
https://alive2.llvm.org/ce/z/_tYEGy

Author: rotateright

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -2171,7 +2171,7 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) {
   // umax(X, Op1) - Op1 --> usub.sat(X, Op1)
   // TODO: The one-use restriction is not strictly necessary, but it may
   //       require improving other pattern matching and/or codegen.
-  if (match(Op0, m_OneUse(m_UMax(m_Value(X), m_Specific(Op1)))))
+  if (match(Op0, m_OneUse(m_c_UMax(m_Value(X), m_Specific(Op1)))))
     return replaceInstUsesWith(
         I, Builder.CreateIntrinsic(Intrinsic::usub_sat, {Ty}, {X, Op1}));
 

llvm/test/Transforms/InstCombine/sub-minmax.ll

@@ -501,9 +501,8 @@ define i8 @umin_not_sub_intrinsic_uses(i8 %x, i8 %y) {
 
 define i8 @umax_sub_op0(i8 %x, i8 %y) {
 ; CHECK-LABEL: @umax_sub_op0(
-; CHECK-NEXT:    [[U:%.*]] = call i8 @llvm.umax.i8(i8 [[Y:%.*]], i8 [[X:%.*]])
-; CHECK-NEXT:    [[R:%.*]] = sub i8 [[U]], [[Y]]
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i8 @llvm.usub.sat.i8(i8 [[X:%.*]], i8 [[Y:%.*]])
+; CHECK-NEXT:    ret i8 [[TMP1]]
 ;
   %u = call i8 @llvm.umax.i8(i8 %y, i8 %x)
   %r = sub i8 %u, %y