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Recommit r317510 "[InstCombine] Pull shifts through a select plus bin…
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…op with constant"

The hexagon test should be fixed now.

Original commit message:

This pulls shifts through a select+binop with a constant where the select conditionally executes the binop. We already do this for just the binop, but not with the select.

This can allow us to get the select closer to other selects to enable removing one.

Differential Revision: https://reviews.llvm.org/D39222

llvm-svn: 317600
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@topperc
topperc committed Nov 7, 2017
1 parent f4bf422 commit 7dd4d32
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Showing 2 changed files with 342 additions and 27 deletions.
109 changes: 82 additions & 27 deletions llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -310,6 +310,40 @@ static Value *getShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
}
}

// If this is a bitwise operator or add with a constant RHS we might be able
// to pull it through a shift.
static bool canShiftBinOpWithConstantRHS(BinaryOperator &Shift,
BinaryOperator *BO,
const APInt &C) {
bool IsValid = true; // Valid only for And, Or Xor,
bool HighBitSet = false; // Transform ifhigh bit of constant set?

switch (BO->getOpcode()) {
default: IsValid = false; break; // Do not perform transform!
case Instruction::Add:
IsValid = Shift.getOpcode() == Instruction::Shl;
break;
case Instruction::Or:
case Instruction::Xor:
HighBitSet = false;
break;
case Instruction::And:
HighBitSet = true;
break;
}

// If this is a signed shift right, and the high bit is modified
// by the logical operation, do not perform the transformation.
// The HighBitSet boolean indicates the value of the high bit of
// the constant which would cause it to be modified for this
// operation.
//
if (IsValid && Shift.getOpcode() == Instruction::AShr)
IsValid = C.isNegative() == HighBitSet;

return IsValid;
}

Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, Constant *Op1,
BinaryOperator &I) {
bool isLeftShift = I.getOpcode() == Instruction::Shl;
Expand Down Expand Up @@ -472,33 +506,7 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, Constant *Op1,
// shift is the only use, we can pull it out of the shift.
const APInt *Op0C;
if (match(Op0BO->getOperand(1), m_APInt(Op0C))) {
bool isValid = true; // Valid only for And, Or, Xor
bool highBitSet = false; // Transform if high bit of constant set?

switch (Op0BO->getOpcode()) {
default: isValid = false; break; // Do not perform transform!
case Instruction::Add:
isValid = isLeftShift;
break;
case Instruction::Or:
case Instruction::Xor:
highBitSet = false;
break;
case Instruction::And:
highBitSet = true;
break;
}

// If this is a signed shift right, and the high bit is modified
// by the logical operation, do not perform the transformation.
// The highBitSet boolean indicates the value of the high bit of
// the constant which would cause it to be modified for this
// operation.
//
if (isValid && I.getOpcode() == Instruction::AShr)
isValid = Op0C->isNegative() == highBitSet;

if (isValid) {
if (canShiftBinOpWithConstantRHS(I, Op0BO, *Op0C)) {
Constant *NewRHS = ConstantExpr::get(I.getOpcode(),
cast<Constant>(Op0BO->getOperand(1)), Op1);

Expand All @@ -525,6 +533,53 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, Constant *Op1,
return BinaryOperator::CreateSub(NewRHS, NewShift);
}
}

// If we have a select that conditionally executes some binary operator,
// see if we can pull it the select and operator through the shift.
//
// For example, turning:
// shl (select C, (add X, C1), X), C2
// Into:
// Y = shl X, C2
// select C, (add Y, C1 << C2), Y
Value *Cond;
BinaryOperator *TBO;
Value *FalseVal;
if (match(Op0, m_Select(m_Value(Cond), m_OneUse(m_BinOp(TBO)),
m_Value(FalseVal)))) {
const APInt *C;
if (!isa<Constant>(FalseVal) && TBO->getOperand(0) == FalseVal &&
match(TBO->getOperand(1), m_APInt(C)) &&
canShiftBinOpWithConstantRHS(I, TBO, *C)) {
Constant *NewRHS = ConstantExpr::get(I.getOpcode(),
cast<Constant>(TBO->getOperand(1)), Op1);

Value *NewShift =
Builder.CreateBinOp(I.getOpcode(), FalseVal, Op1);
Value *NewOp = Builder.CreateBinOp(TBO->getOpcode(), NewShift,
NewRHS);
return SelectInst::Create(Cond, NewOp, NewShift);
}
}

BinaryOperator *FBO;
Value *TrueVal;
if (match(Op0, m_Select(m_Value(Cond), m_Value(TrueVal),
m_OneUse(m_BinOp(FBO))))) {
const APInt *C;
if (!isa<Constant>(TrueVal) && FBO->getOperand(0) == TrueVal &&
match(FBO->getOperand(1), m_APInt(C)) &&
canShiftBinOpWithConstantRHS(I, FBO, *C)) {
Constant *NewRHS = ConstantExpr::get(I.getOpcode(),
cast<Constant>(FBO->getOperand(1)), Op1);

Value *NewShift =
Builder.CreateBinOp(I.getOpcode(), TrueVal, Op1);
Value *NewOp = Builder.CreateBinOp(FBO->getOpcode(), NewShift,
NewRHS);
return SelectInst::Create(Cond, NewShift, NewOp);
}
}
}

return nullptr;
Expand Down
260 changes: 260 additions & 0 deletions llvm/test/Transforms/InstCombine/shift.ll
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1332,3 +1332,263 @@ define i7 @test65(i7 %a, i7 %b) {
%y = and i7 %x, 1 ; this extracts the lsb which should be 0 because we shifted an even number of bits and all even bits of the shift input are 0.
ret i7 %y
}

define i32 @shl_select_add_true(i32 %x, i1 %cond) {
; CHECK-LABEL: @shl_select_add_true(
; CHECK-NEXT: [[TMP1:%.*]] = shl i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = add i32 [[TMP1]], 14
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP2]], i32 [[TMP1]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = add i32 %x, 7
%2 = select i1 %cond, i32 %1, i32 %x
%3 = shl i32 %2, 1
ret i32 %3
}

define i32 @shl_select_add_false(i32 %x, i1 %cond) {
; CHECK-LABEL: @shl_select_add_false(
; CHECK-NEXT: [[TMP1:%.*]] = shl i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = add i32 [[TMP1]], 14
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP1]], i32 [[TMP2]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = add i32 %x, 7
%2 = select i1 %cond, i32 %x, i32 %1
%3 = shl i32 %2, 1
ret i32 %3
}

define i32 @shl_select_and_true(i32 %x, i1 %cond) {
; CHECK-LABEL: @shl_select_and_true(
; CHECK-NEXT: [[TMP1:%.*]] = shl i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = and i32 [[TMP1]], 14
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP2]], i32 [[TMP1]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = and i32 %x, 7
%2 = select i1 %cond, i32 %1, i32 %x
%3 = shl i32 %2, 1
ret i32 %3
}

define i32 @shl_select_and_false(i32 %x, i1 %cond) {
; CHECK-LABEL: @shl_select_and_false(
; CHECK-NEXT: [[TMP1:%.*]] = shl i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = and i32 [[TMP1]], 14
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP1]], i32 [[TMP2]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = and i32 %x, 7
%2 = select i1 %cond, i32 %x, i32 %1
%3 = shl i32 %2, 1
ret i32 %3
}

define i32 @lshr_select_and_true(i32 %x, i1 %cond) {
; CHECK-LABEL: @lshr_select_and_true(
; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = and i32 [[TMP1]], 3
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP2]], i32 [[TMP1]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = and i32 %x, 7
%2 = select i1 %cond, i32 %1, i32 %x
%3 = lshr i32 %2, 1
ret i32 %3
}

define i32 @lshr_select_and_false(i32 %x, i1 %cond) {
; CHECK-LABEL: @lshr_select_and_false(
; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = and i32 [[TMP1]], 3
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP1]], i32 [[TMP2]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = and i32 %x, 7
%2 = select i1 %cond, i32 %x, i32 %1
%3 = lshr i32 %2, 1
ret i32 %3
}

define i32 @ashr_select_and_true(i32 %x, i1 %cond) {
; CHECK-LABEL: @ashr_select_and_true(
; CHECK-NEXT: [[TMP1:%.*]] = ashr i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = and i32 [[TMP1]], -1073741821
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP2]], i32 [[TMP1]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = and i32 %x, 2147483655
%2 = select i1 %cond, i32 %1, i32 %x
%3 = ashr i32 %2, 1
ret i32 %3
}

define i32 @ashr_select_and_false(i32 %x, i1 %cond) {
; CHECK-LABEL: @ashr_select_and_false(
; CHECK-NEXT: [[TMP1:%.*]] = ashr i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = and i32 [[TMP1]], -1073741821
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP1]], i32 [[TMP2]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = and i32 %x, 2147483655
%2 = select i1 %cond, i32 %x, i32 %1
%3 = ashr i32 %2, 1
ret i32 %3
}

define i32 @shl_select_or_true(i32 %x, i1 %cond) {
; CHECK-LABEL: @shl_select_or_true(
; CHECK-NEXT: [[TMP1:%.*]] = shl i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = or i32 [[TMP1]], 14
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP2]], i32 [[TMP1]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = or i32 %x, 7
%2 = select i1 %cond, i32 %1, i32 %x
%3 = shl i32 %2, 1
ret i32 %3
}

define i32 @shl_select_or_false(i32 %x, i1 %cond) {
; CHECK-LABEL: @shl_select_or_false(
; CHECK-NEXT: [[TMP1:%.*]] = shl i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = or i32 [[TMP1]], 14
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP1]], i32 [[TMP2]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = or i32 %x, 7
%2 = select i1 %cond, i32 %x, i32 %1
%3 = shl i32 %2, 1
ret i32 %3
}

define i32 @lshr_select_or_true(i32 %x, i1 %cond) {
; CHECK-LABEL: @lshr_select_or_true(
; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = or i32 [[TMP1]], 3
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP2]], i32 [[TMP1]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = or i32 %x, 7
%2 = select i1 %cond, i32 %1, i32 %x
%3 = lshr i32 %2, 1
ret i32 %3
}

define i32 @lshr_select_or_false(i32 %x, i1 %cond) {
; CHECK-LABEL: @lshr_select_or_false(
; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = or i32 [[TMP1]], 3
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP1]], i32 [[TMP2]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = or i32 %x, 7
%2 = select i1 %cond, i32 %x, i32 %1
%3 = lshr i32 %2, 1
ret i32 %3
}

define i32 @ashr_select_or_true(i32 %x, i1 %cond) {
; CHECK-LABEL: @ashr_select_or_true(
; CHECK-NEXT: [[TMP1:%.*]] = ashr i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = or i32 [[TMP1]], 3
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP2]], i32 [[TMP1]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = or i32 %x, 7
%2 = select i1 %cond, i32 %1, i32 %x
%3 = ashr i32 %2, 1
ret i32 %3
}

define i32 @ashr_select_or_false(i32 %x, i1 %cond) {
; CHECK-LABEL: @ashr_select_or_false(
; CHECK-NEXT: [[TMP1:%.*]] = ashr i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = or i32 [[TMP1]], 3
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP1]], i32 [[TMP2]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = or i32 %x, 7
%2 = select i1 %cond, i32 %x, i32 %1
%3 = ashr i32 %2, 1
ret i32 %3
}

define i32 @shl_select_xor_true(i32 %x, i1 %cond) {
; CHECK-LABEL: @shl_select_xor_true(
; CHECK-NEXT: [[TMP1:%.*]] = shl i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = xor i32 [[TMP1]], 14
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP2]], i32 [[TMP1]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = xor i32 %x, 7
%2 = select i1 %cond, i32 %1, i32 %x
%3 = shl i32 %2, 1
ret i32 %3
}

define i32 @shl_select_xor_false(i32 %x, i1 %cond) {
; CHECK-LABEL: @shl_select_xor_false(
; CHECK-NEXT: [[TMP1:%.*]] = shl i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = xor i32 [[TMP1]], 14
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP1]], i32 [[TMP2]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = xor i32 %x, 7
%2 = select i1 %cond, i32 %x, i32 %1
%3 = shl i32 %2, 1
ret i32 %3
}

define i32 @lshr_select_xor_true(i32 %x, i1 %cond) {
; CHECK-LABEL: @lshr_select_xor_true(
; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = xor i32 [[TMP1]], 3
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP2]], i32 [[TMP1]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = xor i32 %x, 7
%2 = select i1 %cond, i32 %1, i32 %x
%3 = lshr i32 %2, 1
ret i32 %3
}

define i32 @lshr_select_xor_false(i32 %x, i1 %cond) {
; CHECK-LABEL: @lshr_select_xor_false(
; CHECK-NEXT: [[TMP1:%.*]] = lshr i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = xor i32 [[TMP1]], 3
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP1]], i32 [[TMP2]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = xor i32 %x, 7
%2 = select i1 %cond, i32 %x, i32 %1
%3 = lshr i32 %2, 1
ret i32 %3
}

define i32 @ashr_select_xor_true(i32 %x, i1 %cond) {
; CHECK-LABEL: @ashr_select_xor_true(
; CHECK-NEXT: [[TMP1:%.*]] = ashr i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = xor i32 [[TMP1]], 3
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP2]], i32 [[TMP1]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = xor i32 %x, 7
%2 = select i1 %cond, i32 %1, i32 %x
%3 = ashr i32 %2, 1
ret i32 %3
}

define i32 @ashr_select_xor_false(i32 %x, i1 %cond) {
; CHECK-LABEL: @ashr_select_xor_false(
; CHECK-NEXT: [[TMP1:%.*]] = ashr i32 [[X:%.*]], 1
; CHECK-NEXT: [[TMP2:%.*]] = xor i32 [[TMP1]], 3
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[COND:%.*]], i32 [[TMP1]], i32 [[TMP2]]
; CHECK-NEXT: ret i32 [[TMP3]]
;
%1 = xor i32 %x, 7
%2 = select i1 %cond, i32 %x, i32 %1
%3 = ashr i32 %2, 1
ret i32 %3
}

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