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[InstCombine] (A + 1) + (B ^ -1) --> A - B

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Turn canonicalized subtraction back into (-1 - B) and combine it with (A + 1) into (A - B).
This is similar to the folding already done for (B ^ -1) + Const into (-1 + Const) - B.

Differential Revision: https://reviews.llvm.org/D48535

llvm-svn: 335579
This commit is contained in:
Gil Rapaport
2018-06-26 05:31:18 +00:00
parent 08dae1682d
commit da2e2caa6c
2 changed files with 42 additions and 0 deletions
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5
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
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@@ -1212,6 +1212,11 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
if (Value *V = checkForNegativeOperand(I, Builder))
return replaceInstUsesWith(I, V);
// (A + 1) + ~B --> A - B
// ~B + (A + 1) --> A - B
if (match(&I, m_c_BinOp(m_Add(m_Value(A), m_One()), m_Not(m_Value(B)))))
return BinaryOperator::CreateSub(A, B);
// X % C0 + (( X / C0 ) % C1) * C0 => X % (C0 * C1)
if (Value *V = SimplifyAddWithRemainder(I)) return replaceInstUsesWith(I, V);

37
llvm/test/Transforms/InstCombine/add.ll
View File

@@ -802,3 +802,40 @@ final:
%value = add <2 x i32> <i32 123, i32 333>, %A
ret <2 x i32> %value
}
; E = (A + 1) + ~B = A - B
define i32 @add_not_increment(i32 %A, i32 %B) {
; CHECK-LABEL: @add_not_increment(
; CHECK-NEXT: [[E:%.*]] = sub i32 %A, %B
; CHECK-NEXT: ret i32 [[E]]
;
%C = xor i32 %B, -1
%D = add i32 %A, 1
%E = add i32 %D, %C
ret i32 %E
}
; E = (A + 1) + ~B = A - B
define <2 x i32> @add_not_increment_vec(<2 x i32> %A, <2 x i32> %B) {
; CHECK-LABEL: @add_not_increment_vec(
; CHECK-NEXT: [[E:%.*]] = sub <2 x i32> %A, %B
; CHECK-NEXT: ret <2 x i32> [[E]]
;
%C = xor <2 x i32> %B, <i32 -1, i32 -1>
%D = add <2 x i32> %A, <i32 1, i32 1>
%E = add <2 x i32> %D, %C
ret <2 x i32> %E
}
; E = ~B + (1 + A) = A - B
define i32 @add_not_increment_commuted(i32 %A, i32 %B) {
; CHECK-LABEL: @add_not_increment_commuted(
; CHECK-NEXT: [[E:%.*]] = sub i32 %A, %B
; CHECK-NEXT: ret i32 [[E]]
;
%C = xor i32 %B, -1
%D = add i32 %A, 1
%E = add i32 %C, %D
ret i32 %E
}