From: Sanjay Patel <spatel@rotateright.com>
Date: Sun, 29 Jul 2018 18:13:16 +0000 (+0000)
Subject: [InstCombine] try to fold 'add+sub' to 'not+add'
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=19a2e2a495feab825a915c32b2f9a7c95313c6fa;p=llvm

[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.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@338221 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index e79bdf75d40..aa66b442b07 100644
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1614,6 +1614,14 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
   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;
diff --git a/test/Transforms/InstCombine/sub-not.ll b/test/Transforms/InstCombine/sub-not.ll
index 9335fdafcc1..cd1f8f3bd52 100644
--- a/test/Transforms/InstCombine/sub-not.ll
+++ b/test/Transforms/InstCombine/sub-not.ll
@@ -75,8 +75,8 @@ define <2 x i8> @dec_sub_vec(<2 x i8> %x, <2 x i8> %y) {
 
 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 %y) {
 
 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, <2 x i8> %y) {
 
 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 %y) {
 
 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>