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[InstCombine] Teach foldSelectICmpAnd to recognize a (icmp slt X, 0) …
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…and (icmp sgt X, -1) as equivalent to an and with the sign bit of the truncated type

This is similar to what was already done in foldSelectICmpAndOr. Ultimately I'd like to see if we can call foldSelectICmpAnd from foldSelectIntoOp if we detect a power of 2 constant. This would allow us to remove foldSelectICmpAndOr entirely.

Differential Revision: https://reviews.llvm.org/D36498

llvm-svn: 311362
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@topperc
topperc committed Aug 21, 2017
1 parent a8c329b commit 74177e1
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Showing 2 changed files with 151 additions and 19 deletions.
68 changes: 49 additions & 19 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
View file
Expand Up @@ -594,6 +594,15 @@ canonicalizeMinMaxWithConstant(SelectInst &Sel, ICmpInst &Cmp,
/// icmp instruction with zero, and we have an 'and' with the non-constant value
/// and a power of two we can turn the select into a shift on the result of the
/// 'and'.
/// This folds:
/// select (icmp eq (and X, C1)), C2, C3
/// iff C1 is a power 2 and the difference between C2 and C3 is a power of 2.
/// To something like:
/// (shr (and (X, C1)), (log2(C1) - log2(C2-C3))) + C3
/// Or:
/// (shl (and (X, C1)), (log2(C2-C3) - log2(C1))) + C3
/// With some variations depending if C3 is larger than C2, or the shift
/// isn't needed, or the bit widths don't match.
static Value *foldSelectICmpAnd(Type *SelType, const ICmpInst *IC,
APInt TrueVal, APInt FalseVal,
InstCombiner::BuilderTy &Builder) {
Expand All @@ -603,16 +612,32 @@ static Value *foldSelectICmpAnd(Type *SelType, const ICmpInst *IC,
if (SelType->isVectorTy() != IC->getType()->isVectorTy())
return nullptr;

if (!IC->isEquality())
return nullptr;
Value *V;
APInt AndMask;
bool CreateAnd = false;
ICmpInst::Predicate Pred = IC->getPredicate();
if (ICmpInst::isEquality(Pred)) {
if (!match(IC->getOperand(1), m_Zero()))
return nullptr;

if (!match(IC->getOperand(1), m_Zero()))
return nullptr;
V = IC->getOperand(0);

const APInt *AndRHS;
if (!match(V, m_And(m_Value(), m_Power2(AndRHS))))
return nullptr;

AndMask = *AndRHS;
} else if (decomposeBitTestICmp(IC->getOperand(0), IC->getOperand(1),
Pred, V, AndMask)) {
assert(ICmpInst::isEquality(Pred) && "Not equality test?");

if (!AndMask.isPowerOf2())
return nullptr;

const APInt *AndRHS;
Value *LHS = IC->getOperand(0);
if (!match(LHS, m_And(m_Value(), m_Power2(AndRHS))))
CreateAnd = true;
} else {
return nullptr;
}

// If both select arms are non-zero see if we have a select of the form
// 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic
Expand All @@ -639,11 +664,15 @@ static Value *foldSelectICmpAnd(Type *SelType, const ICmpInst *IC,
// desired result.
const APInt &ValC = !TrueVal.isNullValue() ? TrueVal : FalseVal;
unsigned ValZeros = ValC.logBase2();
unsigned AndZeros = AndRHS->logBase2();
unsigned AndZeros = AndMask.logBase2();

if (CreateAnd) {
// Insert the AND instruction on the input to the truncate.
V = Builder.CreateAnd(V, ConstantInt::get(V->getType(), AndMask));
}

// If types don't match we can still convert the select by introducing a zext
// or a trunc of the 'and'.
Value *V = LHS;
if (ValZeros > AndZeros) {
V = Builder.CreateZExtOrTrunc(V, SelType);
V = Builder.CreateShl(V, ValZeros - AndZeros);
Expand All @@ -656,7 +685,7 @@ static Value *foldSelectICmpAnd(Type *SelType, const ICmpInst *IC,
// Okay, now we know that everything is set up, we just don't know whether we
// have a icmp_ne or icmp_eq and whether the true or false val is the zero.
bool ShouldNotVal = !TrueVal.isNullValue();
ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
ShouldNotVal ^= Pred == ICmpInst::ICMP_NE;
if (ShouldNotVal)
V = Builder.CreateXor(V, ValC);

Expand All @@ -672,15 +701,6 @@ Instruction *InstCombiner::foldSelectInstWithICmp(SelectInst &SI,
Value *TrueVal = SI.getTrueValue();
Value *FalseVal = SI.getFalseValue();

{
const APInt *TrueValC, *FalseValC;
if (match(TrueVal, m_APInt(TrueValC)) &&
match(FalseVal, m_APInt(FalseValC)))
if (Value *V = foldSelectICmpAnd(SI.getType(), ICI, *TrueValC,
*FalseValC, Builder))
return replaceInstUsesWith(SI, V);
}

if (Instruction *NewSel = canonicalizeMinMaxWithConstant(SI, *ICI, Builder))
return NewSel;

Expand All @@ -695,6 +715,7 @@ Instruction *InstCombiner::foldSelectInstWithICmp(SelectInst &SI,
// FIXME: Type and constness constraints could be lifted, but we have to
// watch code size carefully. We should consider xor instead of
// sub/add when we decide to do that.
// TODO: Merge this with foldSelectICmpAnd somehow.
if (CmpLHS->getType()->isIntOrIntVectorTy() &&
CmpLHS->getType() == TrueVal->getType()) {
const APInt *C1, *C2;
Expand Down Expand Up @@ -725,6 +746,15 @@ Instruction *InstCombiner::foldSelectInstWithICmp(SelectInst &SI,
}
}

{
const APInt *TrueValC, *FalseValC;
if (match(TrueVal, m_APInt(TrueValC)) &&
match(FalseVal, m_APInt(FalseValC)))
if (Value *V = foldSelectICmpAnd(SI.getType(), ICI, *TrueValC,
*FalseValC, Builder))
return replaceInstUsesWith(SI, V);
}

// NOTE: if we wanted to, this is where to detect integer MIN/MAX

if (CmpRHS != CmpLHS && isa<Constant>(CmpRHS)) {
Expand Down
102 changes: 102 additions & 0 deletions llvm/test/Transforms/InstCombine/select-with-bitwise-ops.ll
View file
Expand Up @@ -395,6 +395,108 @@ define i8 @test70(i8 %x, i8 %y) {
ret i8 %select
}

define i32 @test71(i32 %x) {
; CHECK-LABEL: @test71(
; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[X:%.*]], 6
; CHECK-NEXT: [[TMP2:%.*]] = and i32 [[TMP1]], 2
; CHECK-NEXT: [[TMP3:%.*]] = xor i32 [[TMP2]], 42
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = and i32 %x, 128
%2 = icmp ne i32 %1, 0
%3 = select i1 %2, i32 40, i32 42
ret i32 %3
}

define <2 x i32> @test71vec(<2 x i32> %x) {
; CHECK-LABEL: @test71vec(
; CHECK-NEXT: [[TMP1:%.*]] = lshr <2 x i32> [[X:%.*]], <i32 6, i32 6>
; CHECK-NEXT: [[TMP2:%.*]] = and <2 x i32> [[TMP1]], <i32 2, i32 2>
; CHECK-NEXT: [[TMP3:%.*]] = xor <2 x i32> [[TMP2]], <i32 42, i32 42>
; CHECK-NEXT: ret <2 x i32> [[TMP3]]
;
%1 = and <2 x i32> %x, <i32 128, i32 128>
%2 = icmp ne <2 x i32> %1, <i32 0, i32 0>
%3 = select <2 x i1> %2, <2 x i32> <i32 40, i32 40>, <2 x i32> <i32 42, i32 42>
ret <2 x i32> %3
}

define i32 @test72(i32 %x) {
; CHECK-LABEL: @test72(
; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[X:%.*]], 6
; CHECK-NEXT: [[TMP2:%.*]] = and i32 [[TMP1]], 2
; CHECK-NEXT: [[TMP3:%.*]] = or i32 [[TMP2]], 40
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = and i32 %x, 128
%2 = icmp eq i32 %1, 0
%3 = select i1 %2, i32 40, i32 42
ret i32 %3
}

define <2 x i32> @test72vec(<2 x i32> %x) {
; CHECK-LABEL: @test72vec(
; CHECK-NEXT: [[TMP1:%.*]] = lshr <2 x i32> [[X:%.*]], <i32 6, i32 6>
; CHECK-NEXT: [[TMP2:%.*]] = and <2 x i32> [[TMP1]], <i32 2, i32 2>
; CHECK-NEXT: [[TMP3:%.*]] = or <2 x i32> [[TMP2]], <i32 40, i32 40>
; CHECK-NEXT: ret <2 x i32> [[TMP3]]
;
%1 = and <2 x i32> %x, <i32 128, i32 128>
%2 = icmp eq <2 x i32> %1, <i32 0, i32 0>
%3 = select <2 x i1> %2, <2 x i32> <i32 40, i32 40>, <2 x i32> <i32 42, i32 42>
ret <2 x i32> %3
}

define i32 @test73(i32 %x) {
; CHECK-LABEL: @test73(
; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[X:%.*]], 6
; CHECK-NEXT: [[TMP2:%.*]] = and i32 [[TMP1]], 2
; CHECK-NEXT: [[TMP3:%.*]] = or i32 [[TMP2]], 40
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = trunc i32 %x to i8
%2 = icmp sgt i8 %1, -1
%3 = select i1 %2, i32 40, i32 42
ret i32 %3
}

define <2 x i32> @test73vec(<2 x i32> %x) {
; CHECK-LABEL: @test73vec(
; CHECK-NEXT: [[TMP1:%.*]] = lshr <2 x i32> [[X:%.*]], <i32 6, i32 6>
; CHECK-NEXT: [[TMP2:%.*]] = and <2 x i32> [[TMP1]], <i32 2, i32 2>
; CHECK-NEXT: [[TMP3:%.*]] = or <2 x i32> [[TMP2]], <i32 40, i32 40>
; CHECK-NEXT: ret <2 x i32> [[TMP3]]
;
%1 = trunc <2 x i32> %x to <2 x i8>
%2 = icmp sgt <2 x i8> %1, <i8 -1, i8 -1>
%3 = select <2 x i1> %2, <2 x i32> <i32 40, i32 40>, <2 x i32> <i32 42, i32 42>
ret <2 x i32> %3
}

define i32 @test74(i32 %x) {
; CHECK-LABEL: @test74(
; CHECK-NEXT: [[TMP1:%.*]] = ashr i32 [[X:%.*]], 31
; CHECK-NEXT: [[TMP2:%.*]] = and i32 [[TMP1]], 2
; CHECK-NEXT: [[TMP3:%.*]] = or i32 [[TMP2]], 40
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = icmp sgt i32 %x, -1
%2 = select i1 %1, i32 40, i32 42
ret i32 %2
}

define <2 x i32> @test74vec(<2 x i32> %x) {
; CHECK-LABEL: @test74vec(
; CHECK-NEXT: [[TMP1:%.*]] = ashr <2 x i32> [[X:%.*]], <i32 31, i32 31>
; CHECK-NEXT: [[TMP2:%.*]] = and <2 x i32> [[TMP1]], <i32 2, i32 2>
; CHECK-NEXT: [[TMP3:%.*]] = or <2 x i32> [[TMP2]], <i32 40, i32 40>
; CHECK-NEXT: ret <2 x i32> [[TMP3]]
;
%1 = icmp sgt <2 x i32> %x, <i32 -1, i32 -1>
%2 = select <2 x i1> %1, <2 x i32> <i32 40, i32 40>, <2 x i32> <i32 42, i32 42>
ret <2 x i32> %2
}

define i32 @shift_no_xor_multiuse_or(i32 %x, i32 %y) {
; CHECK-LABEL: @shift_no_xor_multiuse_or(
; CHECK-NEXT: [[OR:%.*]] = or i32 [[Y:%.*]], 2
Expand Down

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