[llvm] r338221 - [InstCombine] try to fold 'add+sub' to 'not+add'

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Sun Jul 29 11:13:16 2018
New Revision: 338221

URL: http://llvm.org/viewvc/llvm-project?rev=338221&view=rev
Log:
[InstCombine] try to fold 'add+sub' to 'not+add'

These are reassociated versions of the same pattern and
similar transforms as in rL338200 and rL338118.

The motivation is identical to those commits:
Patterns with add/sub combos can be improved using
'not' ops. This is better for analysis and may lead
to follow-on transforms because 'xor' and 'add' are
commutative/associative. It can also help codegen.


Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
    llvm/trunk/test/Transforms/InstCombine/sub-not.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp?rev=338221&r1=338220&r2=338221&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAddSub.cpp Sun Jul 29 11:13:16 2018
@@ -1614,6 +1614,14 @@ Instruction *InstCombiner::visitSub(Bina
   if (match(Op0, m_Not(m_Value(X))) && match(Op1, m_Not(m_Value(Y))))
     return BinaryOperator::CreateSub(Y, X);
 
+  // (X + -1) - Y --> ~Y + X
+  if (match(Op0, m_OneUse(m_Add(m_Value(X), m_AllOnes()))))
+    return BinaryOperator::CreateAdd(Builder.CreateNot(Op1), X);
+
+  // Y - (X + 1) --> ~X + Y
+  if (match(Op1, m_OneUse(m_Add(m_Value(X), m_One()))))
+    return BinaryOperator::CreateAdd(Builder.CreateNot(X), Op0);
+
   if (Constant *C = dyn_cast<Constant>(Op0)) {
     bool IsNegate = match(C, m_ZeroInt());
     Value *X;

Modified: llvm/trunk/test/Transforms/InstCombine/sub-not.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/sub-not.ll?rev=338221&r1=338220&r2=338221&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/sub-not.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/sub-not.ll Sun Jul 29 11:13:16 2018
@@ -75,8 +75,8 @@ define <2 x i8> @dec_sub_vec(<2 x i8> %x
 
 define i8 @sub_inc(i8 %x, i8 %y) {
 ; CHECK-LABEL: @sub_inc(
-; CHECK-NEXT:    [[S:%.*]] = add i8 [[X:%.*]], 1
-; CHECK-NEXT:    [[R:%.*]] = sub i8 [[Y:%.*]], [[S]]
+; CHECK-NEXT:    [[TMP1:%.*]] = xor i8 [[X:%.*]], -1
+; CHECK-NEXT:    [[R:%.*]] = add i8 [[TMP1]], [[Y:%.*]]
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %s = add i8 %x, 1
@@ -99,8 +99,8 @@ define i8 @sub_inc_extra_use(i8 %x, i8 %
 
 define <2 x i8> @sub_inc_vec(<2 x i8> %x, <2 x i8> %y) {
 ; CHECK-LABEL: @sub_inc_vec(
-; CHECK-NEXT:    [[S:%.*]] = add <2 x i8> [[X:%.*]], <i8 undef, i8 1>
-; CHECK-NEXT:    [[R:%.*]] = sub <2 x i8> [[Y:%.*]], [[S]]
+; CHECK-NEXT:    [[TMP1:%.*]] = xor <2 x i8> [[X:%.*]], <i8 -1, i8 -1>
+; CHECK-NEXT:    [[R:%.*]] = add <2 x i8> [[TMP1]], [[Y:%.*]]
 ; CHECK-NEXT:    ret <2 x i8> [[R]]
 ;
   %s = add <2 x i8> %x, <i8 undef, i8 1>
@@ -110,8 +110,8 @@ define <2 x i8> @sub_inc_vec(<2 x i8> %x
 
 define i8 @sub_dec(i8 %x, i8 %y) {
 ; CHECK-LABEL: @sub_dec(
-; CHECK-NEXT:    [[S:%.*]] = add i8 [[X:%.*]], -1
-; CHECK-NEXT:    [[R:%.*]] = sub i8 [[S]], [[Y:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = xor i8 [[Y:%.*]], -1
+; CHECK-NEXT:    [[R:%.*]] = add i8 [[TMP1]], [[X:%.*]]
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %s = add i8 %x, -1
@@ -134,8 +134,8 @@ define i8 @sub_dec_extra_use(i8 %x, i8 %
 
 define <2 x i8> @sub_dec_vec(<2 x i8> %x, <2 x i8> %y) {
 ; CHECK-LABEL: @sub_dec_vec(
-; CHECK-NEXT:    [[S:%.*]] = add <2 x i8> [[X:%.*]], <i8 undef, i8 -1>
-; CHECK-NEXT:    [[R:%.*]] = sub <2 x i8> [[S]], [[Y:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = xor <2 x i8> [[Y:%.*]], <i8 -1, i8 -1>
+; CHECK-NEXT:    [[R:%.*]] = add <2 x i8> [[TMP1]], [[X:%.*]]
 ; CHECK-NEXT:    ret <2 x i8> [[R]]
 ;
   %s = add <2 x i8> %x, <i8 undef, i8 -1>