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[InstCombine] squash is-power-of-2 that uses ctpop 

This is another intermediate IR step towards solving PR42314:
https://bugs.llvm.org/show_bug.cgi?id=42314

We can test if a value is power-of-2-or-0 using ctpop(X) < 2,
so combining that with a non-zero check of the input is the
same as testing if exactly 1 bit is set:

(X != 0) && (ctpop(X) u< 2) --> ctpop(X) == 1

Differential Revision: https://reviews.llvm.org/D63660

llvm-svn: 364153
This commit is contained in:
Sanjay Patel 2019-06-23 14:22:37 +00:00
parent 6620e3b2f6
commit 13a5ae58fc
2 changed files with 39 additions and 10 deletions
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23
llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
View File

@ -1021,6 +1021,26 @@ static Value *foldSignedTruncationCheck(ICmpInst *ICmp0, ICmpInst *ICmp1,
CxtI.getName() + ".simplified");
}
/// Reduce a pair of compares that check if a value has exactly 1 bit set.
static Value *foldIsPowerOf2(ICmpInst *Cmp0, ICmpInst *Cmp1,
InstCombiner::BuilderTy &Builder) {
// Handle 'and' commutation: make the not-equal compare the first operand.
if (Cmp1->getPredicate() == ICmpInst::ICMP_NE)
std::swap(Cmp0, Cmp1);
// (X != 0) && (ctpop(X) u< 2) --> ctpop(X) == 1
CmpInst::Predicate Pred0, Pred1;
Value *X;
if (match(Cmp0, m_ICmp(Pred0, m_Value(X), m_ZeroInt())) &&
match(Cmp1, m_ICmp(Pred1, m_Intrinsic<Intrinsic::ctpop>(m_Specific(X)),
m_SpecificInt(2))) &&
Pred0 == ICmpInst::ICMP_NE && Pred1 == ICmpInst::ICMP_ULT) {
Value *CtPop = Cmp1->getOperand(0);
return Builder.CreateICmpEQ(CtPop, ConstantInt::get(CtPop->getType(), 1));
}
return nullptr;
}
/// Fold (icmp)&(icmp) if possible.
Value *InstCombiner::foldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS,
Instruction &CxtI) {
@ -1063,6 +1083,9 @@ Value *InstCombiner::foldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS,
if (Value *V = foldSignedTruncationCheck(LHS, RHS, CxtI, Builder))
return V;
if (Value *V = foldIsPowerOf2(LHS, RHS, Builder))
return V;
// This only handles icmp of constants: (icmp1 A, C1) & (icmp2 B, C2).
Value *LHS0 = LHS->getOperand(0), *RHS0 = RHS->getOperand(0);
ConstantInt *LHSC = dyn_cast<ConstantInt>(LHS->getOperand(1));

26
llvm/test/Transforms/InstCombine/ispow2.ll
View File

@ -187,13 +187,13 @@ define i1 @is_pow2or0_negate_op_extra_use2(i32 %x) {
declare i32 @llvm.ctpop.i32(i32)
declare <2 x i8> @llvm.ctpop.v2i8(<2 x i8>)
; (X != 0) && (ctpop(X) u< 2) --> ctpop(X) == 1
define i1 @is_pow2_ctpop(i32 %x) {
; CHECK-LABEL: @is_pow2_ctpop(
; CHECK-NEXT: [[T0:%.*]] = tail call i32 @llvm.ctpop.i32(i32 [[X:%.*]]), !range !0
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[T0]], 2
; CHECK-NEXT: [[NOTZERO:%.*]] = icmp ne i32 [[X]], 0
; CHECK-NEXT: [[R:%.*]] = and i1 [[NOTZERO]], [[CMP]]
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i32 [[T0]], 1
; CHECK-NEXT: ret i1 [[TMP1]]
;
%t0 = tail call i32 @llvm.ctpop.i32(i32 %x)
%cmp = icmp ult i32 %t0, 2
@ -212,8 +212,8 @@ define i1 @is_pow2_ctpop_extra_uses(i32 %x) {
; CHECK-NEXT: call void @use_i1(i1 [[CMP]])
; CHECK-NEXT: [[NOTZERO:%.*]] = icmp ne i32 [[X]], 0
; CHECK-NEXT: call void @use_i1(i1 [[NOTZERO]])
; CHECK-NEXT: [[R:%.*]] = and i1 [[NOTZERO]], [[CMP]]
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i32 [[T0]], 1
; CHECK-NEXT: ret i1 [[TMP1]]
;
%t0 = tail call i32 @llvm.ctpop.i32(i32 %x)
%cmp = icmp ult i32 %t0, 2
@ -229,10 +229,8 @@ define i1 @is_pow2_ctpop_extra_uses(i32 %x) {
define <2 x i1> @is_pow2_ctpop_commute_vec(<2 x i8> %x) {
; CHECK-LABEL: @is_pow2_ctpop_commute_vec(
; CHECK-NEXT: [[T0:%.*]] = tail call <2 x i8> @llvm.ctpop.v2i8(<2 x i8> [[X:%.*]])
; CHECK-NEXT: [[CMP:%.*]] = icmp ult <2 x i8> [[T0]], <i8 2, i8 2>
; CHECK-NEXT: [[NOTZERO:%.*]] = icmp ne <2 x i8> [[X]], zeroinitializer
; CHECK-NEXT: [[R:%.*]] = and <2 x i1> [[CMP]], [[NOTZERO]]
; CHECK-NEXT: ret <2 x i1> [[R]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq <2 x i8> [[T0]], <i8 1, i8 1>
; CHECK-NEXT: ret <2 x i1> [[TMP1]]
;
%t0 = tail call <2 x i8> @llvm.ctpop.v2i8(<2 x i8> %x)
%cmp = icmp ult <2 x i8> %t0, <i8 2, i8 2>
@ -241,6 +239,8 @@ define <2 x i1> @is_pow2_ctpop_commute_vec(<2 x i8> %x) {
ret <2 x i1> %r
}
; Negative test - wrong constant.
define i1 @is_pow2_ctpop_wrong_cmp_op1(i32 %x) {
; CHECK-LABEL: @is_pow2_ctpop_wrong_cmp_op1(
; CHECK-NEXT: [[T0:%.*]] = tail call i32 @llvm.ctpop.i32(i32 [[X:%.*]]), !range !0
@ -256,6 +256,8 @@ define i1 @is_pow2_ctpop_wrong_cmp_op1(i32 %x) {
ret i1 %r
}
; Negative test - wrong constant.
define i1 @is_pow2_ctpop_wrong_cmp_op2(i32 %x) {
; CHECK-LABEL: @is_pow2_ctpop_wrong_cmp_op2(
; CHECK-NEXT: [[T0:%.*]] = tail call i32 @llvm.ctpop.i32(i32 [[X:%.*]]), !range !0
@ -271,6 +273,8 @@ define i1 @is_pow2_ctpop_wrong_cmp_op2(i32 %x) {
ret i1 %r
}
; Negative test - wrong predicate.
define i1 @is_pow2_ctpop_wrong_pred1(i32 %x) {
; CHECK-LABEL: @is_pow2_ctpop_wrong_pred1(
; CHECK-NEXT: [[T0:%.*]] = tail call i32 @llvm.ctpop.i32(i32 [[X:%.*]]), !range !0
@ -286,6 +290,8 @@ define i1 @is_pow2_ctpop_wrong_pred1(i32 %x) {
ret i1 %r
}
; Negative test - wrong predicate.
define i1 @is_pow2_ctpop_wrong_pred2(i32 %x) {
; CHECK-LABEL: @is_pow2_ctpop_wrong_pred2(
; CHECK-NEXT: [[T0:%.*]] = tail call i32 @llvm.ctpop.i32(i32 [[X:%.*]]), !range !0