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The patch introduces new way of narrowing complex (>UINT16 variants) solutions.

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The new method introduced under "-lsr-exp-narrow" option (currenlty set to true).

Summary:

The method is based on registers number mathematical expectation and should be
 generally closer to optimal solution.
Please see details in comments to
 "LSRInstance::NarrowSearchSpaceByDeletingCostlyFormulas()" function
 (in lib/Transforms/Scalar/LoopStrengthReduce.cpp).

Reviewers: qcolombet

Differential Revision: http://reviews.llvm.org/D29862

From: Evgeny Stupachenko <evstupac@gmail.com>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@295704 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evgeny Stupachenko 2017-02-21 07:34:40 +00:00
parent f80e7ef629
commit 141320fd99
3 changed files with 161 additions and 3 deletions
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160
lib/Transforms/Scalar/LoopStrengthReduce.cpp
View File

@ -134,6 +134,12 @@ static cl::opt<bool> InsnsCost(
"lsr-insns-cost", cl::Hidden, cl::init(false),
cl::desc("Add instruction count to a LSR cost model"));
// Flag to choose how to narrow complex lsr solution
static cl::opt<bool> LSRExpNarrow(
"lsr-exp-narrow", cl::Hidden, cl::init(true),
cl::desc("Narrow LSR complex solution using"
" expectation of registers number"));
#ifndef NDEBUG
// Stress test IV chain generation.
static cl::opt<bool> StressIVChain(
@ -1095,6 +1101,7 @@ public:
}
bool HasFormulaWithSameRegs(const Formula &F) const;
float getNotSelectedProbability(const SCEV *Reg) const;
bool InsertFormula(const Formula &F);
void DeleteFormula(Formula &F);
void RecomputeRegs(size_t LUIdx, RegUseTracker &Reguses);
@ -1373,6 +1380,15 @@ bool LSRUse::HasFormulaWithSameRegs(const Formula &F) const {
return Uniquifier.count(Key);
}
/// The function returns a probability of selecting formula without Reg.
float LSRUse::getNotSelectedProbability(const SCEV *Reg) const {
unsigned FNum = 0;
for (const Formula &F : Formulae)
if (F.referencesReg(Reg))
FNum++;
return ((float)(Formulae.size() - FNum)) / Formulae.size();
}
/// If the given formula has not yet been inserted, add it to the list, and
/// return true. Return false otherwise. The formula must be in canonical form.
bool LSRUse::InsertFormula(const Formula &F) {
@ -1846,6 +1862,7 @@ class LSRInstance {
void NarrowSearchSpaceByDetectingSupersets();
void NarrowSearchSpaceByCollapsingUnrolledCode();
void NarrowSearchSpaceByRefilteringUndesirableDedicatedRegisters();
void NarrowSearchSpaceByDeletingCostlyFormulas();
void NarrowSearchSpaceByPickingWinnerRegs();
void NarrowSearchSpaceUsingHeuristics();
@ -4247,6 +4264,144 @@ void LSRInstance::NarrowSearchSpaceByRefilteringUndesirableDedicatedRegisters(){
}
}
/// The function delete formulas with high registers number expectation.
/// Assuming we don't know the value of each formula (already delete
/// all inefficient), generate probability of not selecting for each
/// register.
/// For example,
/// Use1:
/// reg(a) + reg({0,+,1})
/// reg(a) + reg({-1,+,1}) + 1
/// reg({a,+,1})
/// Use2:
/// reg(b) + reg({0,+,1})
/// reg(b) + reg({-1,+,1}) + 1
/// reg({b,+,1})
/// Use3:
/// reg(c) + reg(b) + reg({0,+,1})
/// reg(c) + reg({b,+,1})
///
/// Probability of not selecting
/// Use1 Use2 Use3
/// reg(a) (1/3) * 1 * 1
/// reg(b) 1 * (1/3) * (1/2)
/// reg({0,+,1}) (2/3) * (2/3) * (1/2)
/// reg({-1,+,1}) (2/3) * (2/3) * 1
/// reg({a,+,1}) (2/3) * 1 * 1
/// reg({b,+,1}) 1 * (2/3) * (2/3)
/// reg(c) 1 * 1 * 0
///
/// Now count registers number mathematical expectation for each formula:
/// Note that for each use we exclude probability if not selecting for the use.
/// For example for Use1 probability for reg(a) would be just 1 * 1 (excluding
/// probabilty 1/3 of not selecting for Use1).
/// Use1:
/// reg(a) + reg({0,+,1}) 1 + 1/3 -- to be deleted
/// reg(a) + reg({-1,+,1}) + 1 1 + 4/9 -- to be deleted
/// reg({a,+,1}) 1
/// Use2:
/// reg(b) + reg({0,+,1}) 1/2 + 1/3 -- to be deleted
/// reg(b) + reg({-1,+,1}) + 1 1/2 + 2/3 -- to be deleted
/// reg({b,+,1}) 2/3
/// Use3:
/// reg(c) + reg(b) + reg({0,+,1}) 1 + 1/3 + 4/9 -- to be deleted
/// reg(c) + reg({b,+,1}) 1 + 2/3
void LSRInstance::NarrowSearchSpaceByDeletingCostlyFormulas() {
if (EstimateSearchSpaceComplexity() < ComplexityLimit)
return;
// Ok, we have too many of formulae on our hands to conveniently handle.
// Use a rough heuristic to thin out the list.
// Set of Regs wich will be 100% used in final solution.
// Used in each formula of a solution (in example above this is reg(c)).
// We can skip them in calculations.
SmallPtrSet<const SCEV *, 4> UniqRegs;
DEBUG(dbgs() << "The search space is too complex.\n");
// Map each register to probability of not selecting
DenseMap <const SCEV *, float> RegNumMap;
for (const SCEV *Reg : RegUses) {
if (UniqRegs.count(Reg))
continue;
float PNotSel = 1;
for (const LSRUse &LU : Uses) {
if (!LU.Regs.count(Reg))
continue;
float P = LU.getNotSelectedProbability(Reg);
if (P != 0.0)
PNotSel *= P;
else
UniqRegs.insert(Reg);
}
RegNumMap.insert(std::make_pair(Reg, PNotSel));
}
DEBUG(dbgs() << "Narrowing the search space by deleting costly formulas\n");
// Delete formulas where registers number expectation is high.
for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) {
LSRUse &LU = Uses[LUIdx];
// If nothing to delete - continue.
if (LU.Formulae.size() < 2)
continue;
// This is temporary solution to test performance. Float should be
// replaced with round independent type (based on integers) to avoid
// different results for different target builds.
float FMinRegNum = LU.Formulae[0].getNumRegs();
float FMinARegNum = LU.Formulae[0].getNumRegs();
size_t MinIdx = 0;
for (size_t i = 0, e = LU.Formulae.size(); i != e; ++i) {
Formula &F = LU.Formulae[i];
float FRegNum = 0;
float FARegNum = 0;
for (const SCEV *BaseReg : F.BaseRegs) {
if (UniqRegs.count(BaseReg))
continue;
FRegNum += RegNumMap[BaseReg] / LU.getNotSelectedProbability(BaseReg);
if (isa<SCEVAddRecExpr>(BaseReg))
FARegNum +=
RegNumMap[BaseReg] / LU.getNotSelectedProbability(BaseReg);
}
if (const SCEV *ScaledReg = F.ScaledReg) {
if (!UniqRegs.count(ScaledReg)) {
FRegNum +=
RegNumMap[ScaledReg] / LU.getNotSelectedProbability(ScaledReg);
if (isa<SCEVAddRecExpr>(ScaledReg))
FARegNum +=
RegNumMap[ScaledReg] / LU.getNotSelectedProbability(ScaledReg);
}
}
if (FMinRegNum > FRegNum ||
(FMinRegNum == FRegNum && FMinARegNum > FARegNum)) {
FMinRegNum = FRegNum;
FMinARegNum = FARegNum;
MinIdx = i;
}
}
DEBUG(dbgs() << " The formula "; LU.Formulae[MinIdx].print(dbgs());
dbgs() << " with min reg num " << FMinRegNum << '\n');
if (MinIdx != 0)
std::swap(LU.Formulae[MinIdx], LU.Formulae[0]);
while (LU.Formulae.size() != 1) {
DEBUG(dbgs() << " Deleting "; LU.Formulae.back().print(dbgs());
dbgs() << '\n');
LU.Formulae.pop_back();
}
LU.RecomputeRegs(LUIdx, RegUses);
assert(LU.Formulae.size() == 1 && "Should be exactly 1 min regs formula");
Formula &F = LU.Formulae[0];
DEBUG(dbgs() << " Leaving only "; F.print(dbgs()); dbgs() << '\n');
// When we choose the formula, the regs become unique.
UniqRegs.insert(F.BaseRegs.begin(), F.BaseRegs.end());
if (F.ScaledReg)
UniqRegs.insert(F.ScaledReg);
}
DEBUG(dbgs() << "After pre-selection:\n";
print_uses(dbgs()));
}
/// Pick a register which seems likely to be profitable, and then in any use
/// which has any reference to that register, delete all formulae which do not
/// reference that register.
@ -4319,7 +4474,10 @@ void LSRInstance::NarrowSearchSpaceUsingHeuristics() {
NarrowSearchSpaceByDetectingSupersets();
NarrowSearchSpaceByCollapsingUnrolledCode();
NarrowSearchSpaceByRefilteringUndesirableDedicatedRegisters();
NarrowSearchSpaceByPickingWinnerRegs();
if (LSRExpNarrow)
NarrowSearchSpaceByDeletingCostlyFormulas();
else
NarrowSearchSpaceByPickingWinnerRegs();
}
/// This is the recursive solver.

2
test/Transforms/LoopStrengthReduce/2013-01-14-ReuseCast.ll
View File

@ -14,7 +14,7 @@ target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f3
; current LSR cost model.
; CHECK-NOT: = ptrtoint i8* undef to i64
; CHECK: .lr.ph
; CHECK: [[TMP:%[^ ]+]] = add i64 %tmp5, 1
; CHECK: [[TMP:%[^ ]+]] = add i64 %4, 1
; CHECK: sub i64 [[TMP]], %tmp6
; CHECK: ret void
define void @VerifyDiagnosticConsumerTest() unnamed_addr nounwind uwtable align 2 {

2
test/Transforms/LoopStrengthReduce/ARM/ivchain-ARM.ll
View File

@ -139,7 +139,7 @@ for.end: ; preds = %for.body, %entry
; Consequently, we should *not* form any chains.
;
; A9: foldedidx:
; A9: ldrb{{(.w)?}} {{r[0-9]|lr}}, [{{r[0-9]|lr}}, #3]
; A9: ldrb{{(.w)?}} {{r[0-9]|lr}}, [{{r[0-9]|lr}}, #403]
define void @foldedidx(i8* nocapture %a, i8* nocapture %b, i8* nocapture %c) nounwind ssp {
entry:
br label %for.body