[InstCombine] not(sub X, Y) --> add (not X), Y

The tests with constants show a missing optimization.
Analysis for adds is better than subs, so this can also
help with other transforms. And codegen is better with 
adds for targets like x86 (destructive ops, no sub-from).

https://rise4fun.com/Alive/llK

llvm-svn: 338118

Author: rotateright

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -2545,6 +2545,10 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
       }
     }
 
+    // ~(X - Y) --> ~X + Y
+    if (match(NotVal, m_OneUse(m_Sub(m_Value(X), m_Value(Y)))))
+      return BinaryOperator::CreateAdd(Builder.CreateNot(X), Y);
+
     // ~(~X >>s Y) --> (X >>s Y)
     if (match(NotVal, m_AShr(m_Not(m_Value(X)), m_Value(Y))))
       return BinaryOperator::CreateAShr(X, Y);

llvm/test/Transforms/InstCombine/sub-not.ll

@@ -5,8 +5,8 @@ declare void @use(i8)
 
 define i8 @sub_not(i8 %x, i8 %y) {
 ; CHECK-LABEL: @sub_not(
-; CHECK-NEXT:    [[S:%.*]] = sub i8 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = xor i8 [[S]], -1
+; CHECK-NEXT:    [[TMP1:%.*]] = xor i8 [[X:%.*]], -1
+; CHECK-NEXT:    [[R:%.*]] = add i8 [[TMP1]], [[Y:%.*]]
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %s = sub i8 %x, %y
@@ -29,8 +29,8 @@ define i8 @sub_not_extra_use(i8 %x, i8 %y) {
 
 define <2 x i8> @sub_not_vec(<2 x i8> %x, <2 x i8> %y) {
 ; CHECK-LABEL: @sub_not_vec(
-; CHECK-NEXT:    [[S:%.*]] = sub <2 x i8> [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = xor <2 x i8> [[S]], <i8 -1, i8 undef>
+; 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 = sub <2 x i8> %x, %y

llvm/test/Transforms/InstCombine/vector-xor.ll

@@ -194,9 +194,8 @@ define <4 x i32> @test_v4i32_not_sub_splatconst(<4 x i32> %a0) {
 
 define <4 x i32> @test_v4i32_not_sub_const(<4 x i32> %a0) {
 ; CHECK-LABEL: @test_v4i32_not_sub_const(
-; CHECK-NEXT:    [[TMP1:%.*]] = sub <4 x i32> <i32 3, i32 5, i32 -1, i32 15>, [[A0:%.*]]
-; CHECK-NEXT:    [[TMP2:%.*]] = xor <4 x i32> [[TMP1]], <i32 -1, i32 -1, i32 -1, i32 -1>
-; CHECK-NEXT:    ret <4 x i32> [[TMP2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = add <4 x i32> [[A0:%.*]], <i32 -4, i32 -6, i32 0, i32 -16>
+; CHECK-NEXT:    ret <4 x i32> [[TMP1]]
 ;
   %1 = sub <4 x i32> <i32  3, i32  5, i32 -1, i32 15>, %a0
   %2 = xor <4 x i32> <i32 -1, i32 -1, i32 -1, i32 -1>, %1
@@ -205,9 +204,8 @@ define <4 x i32> @test_v4i32_not_sub_const(<4 x i32> %a0) {
 
 define <4 x i32> @test_v4i32_not_sub_const_undef(<4 x i32> %a0) {
 ; CHECK-LABEL: @test_v4i32_not_sub_const_undef(
-; CHECK-NEXT:    [[TMP1:%.*]] = sub <4 x i32> <i32 3, i32 undef, i32 -1, i32 15>, [[A0:%.*]]
-; CHECK-NEXT:    [[TMP2:%.*]] = xor <4 x i32> [[TMP1]], <i32 -1, i32 -1, i32 -1, i32 undef>
-; CHECK-NEXT:    ret <4 x i32> [[TMP2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = add <4 x i32> [[A0:%.*]], <i32 -4, i32 undef, i32 0, i32 -16>
+; CHECK-NEXT:    ret <4 x i32> [[TMP1]]
 ;
   %1 = sub <4 x i32> <i32  3, i32 undef, i32 -1, i32 15>, %a0
   %2 = xor <4 x i32> <i32 -1, i32 -1, i32 -1, i32 undef>, %1