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[SCEV] Recognize binary `xor` as bit-wise `add` 

https://alive2.llvm.org/ce/z/ULuZxB

We could transparently handle wider bitwidths,
by effectively casting iN to <N x i1> and performing the `add`
bit/element -wise, the expression will be rather large,
so let's not do that for now.
This commit is contained in:
Roman Lebedev 2022-02-10 13:12:39 +03:00
parent 503541fa93
commit 73990ff8a7
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GPG Key ID: 083C3EBB4A1689E0
2 changed files with 7 additions and 4 deletions
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3
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -5067,6 +5067,9 @@ static Optional<BinaryOp> MatchBinaryOp(Value *V, DominatorTree &DT) {
// Instcombine turns add of signmask into xor as a strength reduction step.
if (RHSC->getValue().isSignMask())
return BinaryOp(Instruction::Add, Op->getOperand(0), Op->getOperand(1));
// Binary `xor` is a bit-wise `add`.
if (V->getType()->isIntegerTy(1))
return BinaryOp(Instruction::Add, Op->getOperand(0), Op->getOperand(1));
return BinaryOp(Op);
case Instruction::LShr:

8
llvm/test/Analysis/ScalarEvolution/logical-operations.ll
View File

@ -86,7 +86,7 @@ define i1 @binary_xor.i1(i1 %x, i1 %y) {
; CHECK-LABEL: 'binary_xor.i1'
; CHECK-NEXT: Classifying expressions for: @binary_xor.i1
; CHECK-NEXT: %r = xor i1 %x, %y
; CHECK-NEXT: --> %r U: full-set S: full-set
; CHECK-NEXT: --> (%x + %y) U: full-set S: full-set
; CHECK-NEXT: Determining loop execution counts for: @binary_xor.i1
;
%r = xor i1 %x, %y
@ -108,11 +108,11 @@ define i1 @binary_xor.4ops.i1(i1 %x, i1 %y, i1 %z, i1 %a) {
; CHECK-LABEL: 'binary_xor.4ops.i1'
; CHECK-NEXT: Classifying expressions for: @binary_xor.4ops.i1
; CHECK-NEXT: %t0 = xor i1 %x, %y
; CHECK-NEXT: --> %t0 U: full-set S: full-set
; CHECK-NEXT: --> (%x + %y) U: full-set S: full-set
; CHECK-NEXT: %t1 = xor i1 %z, %a
; CHECK-NEXT: --> %t1 U: full-set S: full-set
; CHECK-NEXT: --> (%z + %a) U: full-set S: full-set
; CHECK-NEXT: %r = xor i1 %t0, %t1
; CHECK-NEXT: --> %r U: full-set S: full-set
; CHECK-NEXT: --> (%x + %y + %z + %a) U: full-set S: full-set
; CHECK-NEXT: Determining loop execution counts for: @binary_xor.4ops.i1
;
%t0 = xor i1 %x, %y