[InstCombine] Combine ZExt (B - A) + ZExt(A) to ZExt(B)

Combine ZExt (B - A) + ZExt(A) to ZExt(B)
https://alive2.llvm.org/ce/z/ESUwPi

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D139930

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -1444,6 +1444,13 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
     return BinaryOperator::CreateAnd(A, NewMask);
   }
 
+  // ZExt (B - A) + ZExt(A) --> ZExt(B)
+  if ((match(RHS, m_ZExt(m_Value(A))) &&
+       match(LHS, m_ZExt(m_NUWSub(m_Value(B), m_Specific(A))))) ||
+      (match(LHS, m_ZExt(m_Value(A))) &&
+       match(RHS, m_ZExt(m_NUWSub(m_Value(B), m_Specific(A))))))
+    return new ZExtInst(B, LHS->getType());
+
   // A+B --> A|B iff A and B have no bits set in common.
   if (haveNoCommonBitsSet(LHS, RHS, DL, &AC, &I, &DT))
     return BinaryOperator::CreateOr(LHS, RHS);

llvm/test/Transforms/InstCombine/add.ll

@@ -2337,11 +2337,8 @@ define i8 @mul_not_negpow2(i8 %x) {
 
 define i16 @add_sub_zext(i8 %x, i8 %y) {
 ; CHECK-LABEL: @add_sub_zext(
-; CHECK-NEXT:    [[TMP1:%.*]] = sub nuw i8 [[Y:%.*]], [[X:%.*]]
-; CHECK-NEXT:    [[TMP2:%.*]] = zext i8 [[TMP1]] to i16
-; CHECK-NEXT:    [[TMP3:%.*]] = zext i8 [[X]] to i16
-; CHECK-NEXT:    [[TMP4:%.*]] = add nuw nsw i16 [[TMP2]], [[TMP3]]
-; CHECK-NEXT:    ret i16 [[TMP4]]
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i8 [[Y:%.*]] to i16
+; CHECK-NEXT:    ret i16 [[TMP1]]
 ;
   %1 = sub nuw i8 %y, %x
   %2 = zext i8 %1 to i16
@@ -2352,11 +2349,8 @@ define i16 @add_sub_zext(i8 %x, i8 %y) {
 
 define i16 @add_commute_sub_zext(i8 %x, i8 %y) {
 ; CHECK-LABEL: @add_commute_sub_zext(
-; CHECK-NEXT:    [[TMP1:%.*]] = sub nuw i8 [[Y:%.*]], [[X:%.*]]
-; CHECK-NEXT:    [[TMP2:%.*]] = zext i8 [[TMP1]] to i16
-; CHECK-NEXT:    [[TMP3:%.*]] = zext i8 [[X]] to i16
-; CHECK-NEXT:    [[TMP4:%.*]] = add nuw nsw i16 [[TMP3]], [[TMP2]]
-; CHECK-NEXT:    ret i16 [[TMP4]]
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i8 [[Y:%.*]] to i16
+; CHECK-NEXT:    ret i16 [[TMP1]]
 ;
   %1 = sub nuw i8 %y, %x
   %2 = zext i8 %1 to i16
@@ -2367,11 +2361,8 @@ define i16 @add_commute_sub_zext(i8 %x, i8 %y) {
 
 define <2 x i8> @add_sub_2xi5_zext(<2 x i5> %x, <2 x i5> %y) {
 ; CHECK-LABEL: @add_sub_2xi5_zext(
-; CHECK-NEXT:    [[TMP1:%.*]] = sub nuw <2 x i5> [[Y:%.*]], [[X:%.*]]
-; CHECK-NEXT:    [[TMP2:%.*]] = zext <2 x i5> [[TMP1]] to <2 x i8>
-; CHECK-NEXT:    [[TMP3:%.*]] = zext <2 x i5> [[X]] to <2 x i8>
-; CHECK-NEXT:    [[TMP4:%.*]] = add nuw nsw <2 x i8> [[TMP3]], [[TMP2]]
-; CHECK-NEXT:    ret <2 x i8> [[TMP4]]
+; CHECK-NEXT:    [[TMP1:%.*]] = zext <2 x i5> [[Y:%.*]] to <2 x i8>
+; CHECK-NEXT:    ret <2 x i8> [[TMP1]]
 ;
   %1 = sub nuw <2 x i5> %y, %x
   %2 = zext <2 x i5> %1 to <2 x i8>
@@ -2383,11 +2374,8 @@ define <2 x i8> @add_sub_2xi5_zext(<2 x i5> %x, <2 x i5> %y) {
 
 define i3 @add_commute_sub_i2_zext_i3(i2 %x, i2 %y) {
 ; CHECK-LABEL: @add_commute_sub_i2_zext_i3(
-; CHECK-NEXT:    [[TMP1:%.*]] = sub nuw i2 [[Y:%.*]], [[X:%.*]]
-; CHECK-NEXT:    [[TMP2:%.*]] = zext i2 [[TMP1]] to i3
-; CHECK-NEXT:    [[TMP3:%.*]] = zext i2 [[X]] to i3
-; CHECK-NEXT:    [[TMP4:%.*]] = add nuw i3 [[TMP3]], [[TMP2]]
-; CHECK-NEXT:    ret i3 [[TMP4]]
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i2 [[Y:%.*]] to i3
+; CHECK-NEXT:    ret i3 [[TMP1]]
 ;
   %1 = sub nuw i2 %y, %x
   %2 = zext i2 %1 to i3
@@ -2400,10 +2388,8 @@ define i16 @add_sub_use_zext(i8 %x, i8 %y) {
 ; CHECK-LABEL: @add_sub_use_zext(
 ; CHECK-NEXT:    [[TMP1:%.*]] = sub nuw i8 [[Y:%.*]], [[X:%.*]]
 ; CHECK-NEXT:    call void @use(i8 [[TMP1]])
-; CHECK-NEXT:    [[TMP2:%.*]] = zext i8 [[TMP1]] to i16
-; CHECK-NEXT:    [[TMP3:%.*]] = zext i8 [[X]] to i16
-; CHECK-NEXT:    [[TMP4:%.*]] = add nuw nsw i16 [[TMP2]], [[TMP3]]
-; CHECK-NEXT:    ret i16 [[TMP4]]
+; CHECK-NEXT:    [[TMP2:%.*]] = zext i8 [[Y]] to i16
+; CHECK-NEXT:    ret i16 [[TMP2]]
 ;
   %1 = sub nuw i8 %y, %x
   call void @use(i8 %1)
@@ -2462,11 +2448,7 @@ define i16 @add_no_nuw_sub_commute_zext(i8 %x, i8 %y) {
 
 define i16 @add_sub_zext_constant(i8 %x) {
 ; CHECK-LABEL: @add_sub_zext_constant(
-; CHECK-NEXT:    [[TMP1:%.*]] = sub nuw i8 -2, [[X:%.*]]
-; CHECK-NEXT:    [[TMP2:%.*]] = zext i8 [[TMP1]] to i16
-; CHECK-NEXT:    [[TMP3:%.*]] = zext i8 [[X]] to i16
-; CHECK-NEXT:    [[TMP4:%.*]] = add nuw nsw i16 [[TMP2]], [[TMP3]]
-; CHECK-NEXT:    ret i16 [[TMP4]]
+; CHECK-NEXT:    ret i16 254
 ;
   %1 = sub nuw i8 254, %x
   %2 = zext i8 %1 to i16