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Fix SLPVectorizer commutativity reordering 

The SLPVectorizer had a very crude way of trying to benefit
from associativity: it tried to optimize for splat/broadcast
or in order to have the same operator on the same side.
This is benefitial to the cost model and allows more vectorization
to occur.
This patch improve the logic and make the detection optimal (locally,
we don't look at the full tree but only at the immediate children).

Should fix https://llvm.org/bugs/show_bug.cgi?id=25247

Reviewers: mzolotukhin

Differential Revision: http://reviews.llvm.org/D13996

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 252337
This commit is contained in:
Mehdi Amini 2015-11-06 20:17:51 +00:00
parent 7bcaec83be
commit b0e3192a48
2 changed files with 147 additions and 76 deletions
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145
llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
View File

@ -1941,7 +1941,6 @@ void BoUpSLP::reorderAltShuffleOperands(ArrayRef<Value *> VL,
}
}
// Return true if I should be commuted before adding it's left and right
// operands to the arrays Left and Right.
//
@ -1950,60 +1949,76 @@ void BoUpSLP::reorderAltShuffleOperands(ArrayRef<Value *> VL,
// a splat to lower the vectorizing cost.
static bool shouldReorderOperands(int i, Instruction &I,
SmallVectorImpl<Value *> &Left,
SmallVectorImpl<Value *> &Right) {
SmallVectorImpl<Value *> &Right,
bool AllSameOpcodeLeft,
bool AllSameOpcodeRight, bool SplatLeft,
bool SplatRight) {
Value *VLeft = I.getOperand(0);
Value *VRight = I.getOperand(1);
// If we have "SplatRight", try to see if commuting is needed to preserve it.
if (SplatRight) {
if (VRight == Right[i - 1])
// Preserve SplatRight
return false;
if (VLeft == Right[i - 1]) {
// Commuting would preserve SplatRight, but we don't want to break
// SplatLeft either, i.e. preserve the original order if possible.
// (FIXME: why do we care?)
if (SplatLeft && VLeft == Left[i - 1])
return false;
return true;
}
}
// Symmetrically handle Right side.
if (SplatLeft) {
if (VLeft == Left[i - 1])
// Preserve SplatLeft
return false;
if (VRight == Left[i - 1])
return true;
}
Instruction *ILeft = dyn_cast<Instruction>(VLeft);
Instruction *IRight = dyn_cast<Instruction>(VRight);
// Sort two opcodes. In the code below we try to preserve the ability to use
// broadcast of values instead of individual inserts.
// vl1 = load
// vl2 = phi
// vr1 = load
// vr2 = vr2
// = vl1 x vr1
// = vl2 x vr2
// If we just sorted according to opcode we would leave the first line in
// tact but we would swap vl2 with vr2 because opcode(phi) > opcode(load).
// = vl1 x vr1
// = vr2 x vl2
// Because vr2 and vr1 are from the same load we loose the opportunity of a
// broadcast for the packed right side in the backend: we have [vr1, vl2]
// instead of [vr1, vr2=vr1].
if (ILeft && IRight) {
if (ILeft->getOpcode() > IRight->getOpcode() &&
Right[i - 1] != IRight) {
// Try not to destroy a broad cast for no apparent benefit.
return true;
} else if (ILeft->getOpcode() == IRight->getOpcode() &&
Right[i - 1] == ILeft) {
// Try preserve broadcasts.
return true;
} else if (ILeft->getOpcode() == IRight->getOpcode() &&
Left[i - 1] == IRight) {
// Try preserve broadcasts.
// If we have "AllSameOpcodeRight", try to see if the left operands preserves
// it and not the right, in this case we want to commute.
if (AllSameOpcodeRight) {
unsigned RightPrevOpcode = cast<Instruction>(Right[i - 1])->getOpcode();
if (IRight && RightPrevOpcode == IRight->getOpcode())
// Do not commute, a match on the right preserves AllSameOpcodeRight
return false;
if (ILeft && RightPrevOpcode == ILeft->getOpcode()) {
// We have a match and may want to commute, but first check if there is
// not also a match on the existing operands on the Left to preserve
// AllSameOpcodeLeft, i.e. preserve the original order if possible.
// (FIXME: why do we care?)
if (AllSameOpcodeLeft && ILeft &&
cast<Instruction>(Left[i - 1])->getOpcode() == ILeft->getOpcode())
return false;
return true;
}
return false;
}
// One opcode, put the instruction on the right.
return ILeft != nullptr;
// Symmetrically handle Left side.
if (AllSameOpcodeLeft) {
unsigned LeftPrevOpcode = cast<Instruction>(Left[i - 1])->getOpcode();
if (ILeft && LeftPrevOpcode == ILeft->getOpcode())
return false;
if (IRight && LeftPrevOpcode == IRight->getOpcode())
return true;
}
return false;
}
void BoUpSLP::reorderInputsAccordingToOpcode(ArrayRef<Value *> VL,
SmallVectorImpl<Value *> &Left,
SmallVectorImpl<Value *> &Right) {
SmallVector<Value *, 16> OrigLeft, OrigRight;
if (VL.size()) {
// Peel the first iteration out of the loop since there's nothing
// interesting to do anyway and it simplifies the checks
// interesting to do anyway and it simplifies the checks in the loop.
auto VLeft = cast<Instruction>(VL[0])->getOperand(0);
auto VRight = cast<Instruction>(VL[0])->getOperand(1);
OrigLeft.push_back(VLeft);
OrigRight.push_back(VRight);
if (!isa<Instruction>(VRight) && isa<Instruction>(VLeft))
// Favor having instruction to the right. FIXME: why?
std::swap(VLeft, VRight);
@ -2014,60 +2029,38 @@ void BoUpSLP::reorderInputsAccordingToOpcode(ArrayRef<Value *> VL,
// Keep track if we have instructions with all the same opcode on one side.
bool AllSameOpcodeLeft = isa<Instruction>(Left[0]);
bool AllSameOpcodeRight = isa<Instruction>(Right[0]);
// Keep track if we have one side with all the same value (broadcast).
bool SplatLeft = true;
bool SplatRight = true;
for (unsigned i = 1, e = VL.size(); i != e; ++i) {
Instruction *I = cast<Instruction>(VL[i]);
Value *VLeft = I->getOperand(0);
Value *VRight = I->getOperand(1);
OrigLeft.push_back(VLeft);
OrigRight.push_back(VRight);
Instruction *ILeft = dyn_cast<Instruction>(VLeft);
Instruction *IRight = dyn_cast<Instruction>(VRight);
// Check whether all operands on one side have the same opcode. In this case
// we want to preserve the original order and not make things worse by
// reordering.
if (AllSameOpcodeLeft && ILeft) {
if (Instruction *PLeft = dyn_cast<Instruction>(OrigLeft[i - 1])) {
if (PLeft->getOpcode() != ILeft->getOpcode())
AllSameOpcodeLeft = false;
} else
AllSameOpcodeLeft = false;
}
if (AllSameOpcodeRight && IRight) {
if (Instruction *PRight = dyn_cast<Instruction>(OrigRight[i - 1])) {
if (PRight->getOpcode() != IRight->getOpcode())
AllSameOpcodeRight = false;
} else
AllSameOpcodeRight = false;
}
assert(I->isCommutative() && "Can only process commutative instruction");
// Commute to favor either a splat or maximizing having the same opcodes on
// one side.
if (shouldReorderOperands(i, *I, Left, Right)) {
if (shouldReorderOperands(i, *I, Left, Right, AllSameOpcodeLeft,
AllSameOpcodeRight, SplatLeft, SplatRight)) {
Left.push_back(I->getOperand(1));
Right.push_back(I->getOperand(0));
} else {
Left.push_back(I->getOperand(0));
Right.push_back(I->getOperand(1));
}
// Update Splat* and AllSameOpcode* after the insertion.
SplatRight = SplatRight && (Right[i - 1] == Right[i]);
SplatLeft = SplatLeft && (Left[i - 1] == Left[i]);
AllSameOpcodeLeft = AllSameOpcodeLeft && isa<Instruction>(Left[i]) &&
(cast<Instruction>(Left[i - 1])->getOpcode() ==
cast<Instruction>(Left[i])->getOpcode());
AllSameOpcodeRight = AllSameOpcodeRight && isa<Instruction>(Right[i]) &&
(cast<Instruction>(Right[i - 1])->getOpcode() ==
cast<Instruction>(Right[i])->getOpcode());
}
bool LeftBroadcast = isSplat(Left);
bool RightBroadcast = isSplat(Right);
// If operands end up being broadcast return this operand order.
if (LeftBroadcast || RightBroadcast)
// If one operand end up being broadcast, return this operand order.
if (SplatRight || SplatLeft)
return;
// Don't reorder if the operands where good to begin.
if (AllSameOpcodeRight || AllSameOpcodeLeft) {
Left = OrigLeft;
Right = OrigRight;
}
const DataLayout &DL = F->getParent()->getDataLayout();
// Finally check if we can get longer vectorizable chain by reordering

78
llvm/test/Transforms/SLPVectorizer/X86/commutativity.ll Normal file
View File

@ -0,0 +1,78 @@
; RUN: opt -slp-vectorizer < %s -S | FileCheck %s
; Verify that the SLP vectorizer is able to figure out that commutativity
; offers the possibility to splat/broadcast %c and thus make it profitable
; to vectorize this case
; ModuleID = 'bugpoint-reduced-simplified.bc'
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.11.0"
@cle = external unnamed_addr global [32 x i8], align 16
@cle32 = external unnamed_addr global [32 x i32], align 16
; Check that we correctly detect a splat/broadcast by leveraging the
; commutativity property of `xor`.
; CHECK-LABEL: @splat
; CHECK: store <16 x i8>
define void @splat(i8 %a, i8 %b, i8 %c) {
%1 = xor i8 %c, %a
store i8 %1, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 0), align 16
%2 = xor i8 %a, %c
store i8 %2, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 1)
%3 = xor i8 %a, %c
store i8 %3, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 2)
%4 = xor i8 %a, %c
store i8 %4, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 3)
%5 = xor i8 %c, %a
store i8 %5, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 4)
%6 = xor i8 %c, %b
store i8 %6, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 5)
%7 = xor i8 %c, %a
store i8 %7, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 6)
%8 = xor i8 %c, %b
store i8 %8, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 7)
%9 = xor i8 %a, %c
store i8 %9, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 8)
%10 = xor i8 %a, %c
store i8 %10, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 9)
%11 = xor i8 %a, %c
store i8 %11, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 10)
%12 = xor i8 %a, %c
store i8 %12, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 11)
%13 = xor i8 %a, %c
store i8 %13, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 12)
%14 = xor i8 %a, %c
store i8 %14, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 13)
%15 = xor i8 %a, %c
store i8 %15, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 14)
%16 = xor i8 %a, %c
store i8 %16, i8* getelementptr inbounds ([32 x i8], [32 x i8]* @cle, i64 0, i64 15)
ret void
}
; Check that we correctly detect that we can have the same opcode on one side by
; leveraging the commutativity property of `xor`.
; CHECK-LABEL: @same_opcode_on_one_side
; CHECK: store <4 x i32>
define void @same_opcode_on_one_side(i32 %a, i32 %b, i32 %c) {
%add1 = add i32 %c, %a
%add2 = add i32 %c, %a
%add3 = add i32 %a, %c
%add4 = add i32 %c, %a
%1 = xor i32 %add1, %a
store i32 %1, i32* getelementptr inbounds ([32 x i32], [32 x i32]* @cle32, i64 0, i64 0), align 16
%2 = xor i32 %b, %add2
store i32 %2, i32* getelementptr inbounds ([32 x i32], [32 x i32]* @cle32, i64 0, i64 1)
%3 = xor i32 %c, %add3
store i32 %3, i32* getelementptr inbounds ([32 x i32], [32 x i32]* @cle32, i64 0, i64 2)
%4 = xor i32 %a, %add4
store i32 %4, i32* getelementptr inbounds ([32 x i32], [32 x i32]* @cle32, i64 0, i64 3)
ret void
}