6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2024-08-22 10:29:35 +00:00
Code Issues Projects Releases Wiki Activity

[IRCE] Support half-range checks.

Browse Source 
This change to IRCE gets it to recognize "half" range checks.  Half
range checks are range checks that only either check if the index is
`slt` some positive integer ("length") or if the index is `sge` `0`.

The range solver does not try to be clever / aggressive about solving
half-range checks -- it transforms "I < L" to "0 <= I < L" and "0 <= I"
to "0 <= I < INT_SMAX".  This is safe, but not always optimal.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232444 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjoy Das 2015-03-17 00:42:13 +00:00
parent bdd2212363
commit eaf8532f7a
3 changed files with 228 additions and 130 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

284
lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
View File

@ -96,23 +96,40 @@ namespace {
///
/// and
///
/// 2. a condition that is provably true for some range of values taken by the
/// containing loop's induction variable.
/// 2. a condition that is provably true for some contiguous range of values
/// taken by the containing loop's induction variable.
///
/// Currently all inductive range checks are branches conditional on an
/// expression of the form
///
/// 0 <= (Offset + Scale * I) < Length
///
/// where `I' is the canonical induction variable of a loop to which Offset and
/// Scale are loop invariant, and Length is >= 0. Currently the 'false' branch
/// is considered cold, looking at profiling data to verify that is a TODO.
class InductiveRangeCheck {
// Classifies a range check
enum RangeCheckKind {
// Range check of the form "0 <= I".
RANGE_CHECK_LOWER = 1,
// Range check of the form "I < L" where L is known positive.
RANGE_CHECK_UPPER = 2,
// The logical and of the RANGE_CHECK_LOWER and RANGE_CHECK_UPPER
// conditions.
RANGE_CHECK_BOTH = RANGE_CHECK_LOWER | RANGE_CHECK_UPPER,
// Unrecognized range check condition.
RANGE_CHECK_UNKNOWN = (unsigned)-1
};
static const char *rangeCheckKindToStr(RangeCheckKind);
const SCEV *Offset;
const SCEV *Scale;
Value *Length;
BranchInst *Branch;
RangeCheckKind Kind;
static RangeCheckKind parseRangeCheckICmp(ICmpInst *ICI, ScalarEvolution &SE,
Value *&Index, Value *&Length);
static InductiveRangeCheck::RangeCheckKind
parseRangeCheck(Loop *L, ScalarEvolution &SE, Value *Condition,
const SCEV *&Index, Value *&UpperLimit);
InductiveRangeCheck() :
Offset(nullptr), Scale(nullptr), Length(nullptr), Branch(nullptr) { }
@ -124,13 +141,17 @@ public:
void print(raw_ostream &OS) const {
OS << "InductiveRangeCheck:\n";
OS << " Kind: " << rangeCheckKindToStr(Kind) << "\n";
OS << " Offset: ";
Offset->print(OS);
OS << " Scale: ";
Scale->print(OS);
OS << " Length: ";
Length->print(OS);
OS << " Branch: ";
if (Length)
Length->print(OS);
else
OS << "(null)";
OS << "\n Branch: ";
getBranch()->print(OS);
OS << "\n";
}
@ -207,160 +228,146 @@ char InductiveRangeCheckElimination::ID = 0;
INITIALIZE_PASS(InductiveRangeCheckElimination, "irce",
"Inductive range check elimination", false, false)
static bool IsLowerBoundCheck(Value *Check, Value *&IndexV) {
const char *InductiveRangeCheck::rangeCheckKindToStr(
InductiveRangeCheck::RangeCheckKind RCK) {
switch (RCK) {
case InductiveRangeCheck::RANGE_CHECK_UNKNOWN:
return "RANGE_CHECK_UNKNOWN";
case InductiveRangeCheck::RANGE_CHECK_UPPER:
return "RANGE_CHECK_UPPER";
case InductiveRangeCheck::RANGE_CHECK_LOWER:
return "RANGE_CHECK_LOWER";
case InductiveRangeCheck::RANGE_CHECK_BOTH:
return "RANGE_CHECK_BOTH";
}
llvm_unreachable("unknown range check type!");
}
/// Parse a single ICmp instruction, `ICI`, into a range check. If `ICI`
/// cannot
/// be interpreted as a range check, return `RANGE_CHECK_UNKNOWN` and set
/// `Index` and `Length` to `nullptr`. Otherwise set `Index` to the value
/// being
/// range checked, and set `Length` to the upper limit `Index` is being range
/// checked with if (and only if) the range check type is stronger or equal to
/// RANGE_CHECK_UPPER.
///
InductiveRangeCheck::RangeCheckKind
InductiveRangeCheck::parseRangeCheckICmp(ICmpInst *ICI, ScalarEvolution &SE,
Value *&Index, Value *&Length) {
using namespace llvm::PatternMatch;
ICmpInst::Predicate Pred = ICmpInst::BAD_ICMP_PREDICATE;
Value *LHS = nullptr, *RHS = nullptr;
if (!match(Check, m_ICmp(Pred, m_Value(LHS), m_Value(RHS))))
return false;
ICmpInst::Predicate Pred = ICI->getPredicate();
Value *LHS = ICI->getOperand(0);
Value *RHS = ICI->getOperand(1);
switch (Pred) {
default:
return false;
return RANGE_CHECK_UNKNOWN;
case ICmpInst::ICMP_SLE:
std::swap(LHS, RHS);
// fallthrough
case ICmpInst::ICMP_SGE:
if (!match(RHS, m_ConstantInt<0>()))
return false;
IndexV = LHS;
return true;
if (match(RHS, m_ConstantInt<0>())) {
Index = LHS;
return RANGE_CHECK_LOWER;
}
return RANGE_CHECK_UNKNOWN;
case ICmpInst::ICMP_SLT:
std::swap(LHS, RHS);
// fallthrough
case ICmpInst::ICMP_SGT:
if (!match(RHS, m_ConstantInt<-1>()))
return false;
IndexV = LHS;
return true;
}
}
if (match(RHS, m_ConstantInt<-1>())) {
Index = LHS;
return RANGE_CHECK_LOWER;
}
static bool IsUpperBoundCheck(Value *Check, Value *Index, Value *&UpperLimit) {
using namespace llvm::PatternMatch;
if (SE.isKnownNonNegative(SE.getSCEV(LHS))) {
Index = RHS;
Length = LHS;
return RANGE_CHECK_UPPER;
}
return RANGE_CHECK_UNKNOWN;
ICmpInst::Predicate Pred = ICmpInst::BAD_ICMP_PREDICATE;
Value *LHS = nullptr, *RHS = nullptr;
if (!match(Check, m_ICmp(Pred, m_Value(LHS), m_Value(RHS))))
return false;
switch (Pred) {
default:
return false;
case ICmpInst::ICMP_SGT:
std::swap(LHS, RHS);
// fallthrough
case ICmpInst::ICMP_SLT:
if (LHS != Index)
return false;
UpperLimit = RHS;
return true;
case ICmpInst::ICMP_UGT:
std::swap(LHS, RHS);
// fallthrough
case ICmpInst::ICMP_ULT:
if (LHS != Index)
return false;
UpperLimit = RHS;
return true;
std::swap(LHS, RHS);
// fallthrough
case ICmpInst::ICMP_UGT:
if (SE.isKnownNonNegative(SE.getSCEV(LHS))) {
Index = RHS;
Length = LHS;
return RANGE_CHECK_BOTH;
}
return RANGE_CHECK_UNKNOWN;
}
llvm_unreachable("default clause returns!");
}
/// Split a condition into something semantically equivalent to (0 <= I <
/// Limit), both comparisons signed and Len loop invariant on L and positive.
/// On success, return true and set Index to I and UpperLimit to Limit. Return
/// false on failure (we may still write to UpperLimit and Index on failure).
/// It does not try to interpret I as a loop index.
///
static bool SplitRangeCheckCondition(Loop *L, ScalarEvolution &SE,
/// Parses an arbitrary condition into a range check. `Length` is set only if
/// the range check is recognized to be `RANGE_CHECK_UPPER` or stronger.
InductiveRangeCheck::RangeCheckKind
InductiveRangeCheck::parseRangeCheck(Loop *L, ScalarEvolution &SE,
Value *Condition, const SCEV *&Index,
Value *&UpperLimit) {
// TODO: currently this catches some silly cases like comparing "%idx slt 1".
// Our transformations are still correct, but less likely to be profitable in
// those cases. We have to come up with some heuristics that pick out the
// range checks that are more profitable to clone a loop for. This function
// in general can be made more robust.
Value *&Length) {
using namespace llvm::PatternMatch;
Value *A = nullptr;
Value *B = nullptr;
ICmpInst::Predicate Pred = ICmpInst::BAD_ICMP_PREDICATE;
// In these early checks we assume that the matched UpperLimit is positive.
// We'll verify that fact later, before returning true.
if (match(Condition, m_And(m_Value(A), m_Value(B)))) {
Value *IndexV = nullptr;
Value *ExpectedUpperBoundCheck = nullptr;
Value *IndexA = nullptr, *IndexB = nullptr;
Value *LengthA = nullptr, *LengthB = nullptr;
ICmpInst *ICmpA = dyn_cast<ICmpInst>(A), *ICmpB = dyn_cast<ICmpInst>(B);
if (IsLowerBoundCheck(A, IndexV))
ExpectedUpperBoundCheck = B;
else if (IsLowerBoundCheck(B, IndexV))
ExpectedUpperBoundCheck = A;
else
return false;
if (!ICmpA || !ICmpB)
return InductiveRangeCheck::RANGE_CHECK_UNKNOWN;
if (!IsUpperBoundCheck(ExpectedUpperBoundCheck, IndexV, UpperLimit))
return false;
auto RCKindA = parseRangeCheckICmp(ICmpA, SE, IndexA, LengthA);
auto RCKindB = parseRangeCheckICmp(ICmpB, SE, IndexB, LengthB);
Index = SE.getSCEV(IndexV);
if (RCKindA == InductiveRangeCheck::RANGE_CHECK_UNKNOWN ||
RCKindB == InductiveRangeCheck::RANGE_CHECK_UNKNOWN)
return InductiveRangeCheck::RANGE_CHECK_UNKNOWN;
if (IndexA != IndexB)
return InductiveRangeCheck::RANGE_CHECK_UNKNOWN;
if (LengthA != nullptr && LengthB != nullptr && LengthA != LengthB)
return InductiveRangeCheck::RANGE_CHECK_UNKNOWN;
Index = SE.getSCEV(IndexA);
if (isa<SCEVCouldNotCompute>(Index))
return false;
return InductiveRangeCheck::RANGE_CHECK_UNKNOWN;
} else if (match(Condition, m_ICmp(Pred, m_Value(A), m_Value(B)))) {
switch (Pred) {
default:
return false;
Length = LengthA == nullptr ? LengthB : LengthA;
case ICmpInst::ICMP_SGT:
std::swap(A, B);
// fall through
case ICmpInst::ICMP_SLT:
UpperLimit = B;
Index = SE.getSCEV(A);
if (isa<SCEVCouldNotCompute>(Index) || !SE.isKnownNonNegative(Index))
return false;
break;
case ICmpInst::ICMP_UGT:
std::swap(A, B);
// fall through
case ICmpInst::ICMP_ULT:
UpperLimit = B;
Index = SE.getSCEV(A);
if (isa<SCEVCouldNotCompute>(Index))
return false;
break;
}
} else {
return false;
return (InductiveRangeCheck::RangeCheckKind)(RCKindA | RCKindB);
}
const SCEV *UpperLimitSCEV = SE.getSCEV(UpperLimit);
if (isa<SCEVCouldNotCompute>(UpperLimitSCEV) ||
!SE.isKnownNonNegative(UpperLimitSCEV))
return false;
if (ICmpInst *ICI = dyn_cast<ICmpInst>(Condition)) {
Value *IndexVal = nullptr;
if (SE.getLoopDisposition(UpperLimitSCEV, L) !=
ScalarEvolution::LoopInvariant) {
DEBUG(dbgs() << " in function: " << L->getHeader()->getParent()->getName()
<< " ";
dbgs() << " UpperLimit is not loop invariant: "
<< UpperLimit->getName() << "\n";);
return false;
auto RCKind = parseRangeCheckICmp(ICI, SE, IndexVal, Length);
if (RCKind == InductiveRangeCheck::RANGE_CHECK_UNKNOWN)
return InductiveRangeCheck::RANGE_CHECK_UNKNOWN;
Index = SE.getSCEV(IndexVal);
if (isa<SCEVCouldNotCompute>(Index))
return InductiveRangeCheck::RANGE_CHECK_UNKNOWN;
return RCKind;
}
return true;
return InductiveRangeCheck::RANGE_CHECK_UNKNOWN;
}
@ -380,10 +387,15 @@ InductiveRangeCheck::create(InductiveRangeCheck::AllocatorTy &A, BranchInst *BI,
Value *Length = nullptr;
const SCEV *IndexSCEV = nullptr;
if (!SplitRangeCheckCondition(L, SE, BI->getCondition(), IndexSCEV, Length))
auto RCKind = InductiveRangeCheck::parseRangeCheck(L, SE, BI->getCondition(),
IndexSCEV, Length);
if (RCKind == InductiveRangeCheck::RANGE_CHECK_UNKNOWN)
return nullptr;
assert(IndexSCEV && Length && "contract with SplitRangeCheckCondition!");
assert(IndexSCEV && "contract with SplitRangeCheckCondition!");
assert(!(RCKind & InductiveRangeCheck::RANGE_CHECK_UPPER) ||
Length && "contract with SplitRangeCheckCondition!");
const SCEVAddRecExpr *IndexAddRec = dyn_cast<SCEVAddRecExpr>(IndexSCEV);
bool IsAffineIndex =
@ -397,6 +409,7 @@ InductiveRangeCheck::create(InductiveRangeCheck::AllocatorTy &A, BranchInst *BI,
IRC->Offset = IndexAddRec->getStart();
IRC->Scale = IndexAddRec->getStepRecurrence(SE);
IRC->Branch = BI;
IRC->Kind = RCKind;
return IRC;
}
@ -1294,8 +1307,19 @@ InductiveRangeCheck::computeSafeIterationSpace(ScalarEvolution &SE,
const SCEV *M = SE.getMinusSCEV(C, A);
const SCEV *Begin = SE.getNegativeSCEV(M);
const SCEV *End = SE.getMinusSCEV(SE.getSCEV(getLength()), M);
const SCEV *UpperLimit = nullptr;
// We strengthen "0 <= I" to "0 <= I < INT_SMAX" and "I < L" to "0 <= I < L".
// We can potentially do much better here.
if (Value *V = getLength()) {
UpperLimit = SE.getSCEV(V);
} else {
assert(Kind == InductiveRangeCheck::RANGE_CHECK_LOWER && "invariant!");
unsigned BitWidth = cast<IntegerType>(IndVar->getType())->getBitWidth();
UpperLimit = SE.getConstant(APInt::getSignedMaxValue(BitWidth));
}
const SCEV *End = SE.getMinusSCEV(UpperLimit, M);
return InductiveRangeCheck::Range(Begin, End);
}

37
test/Transforms/IRCE/only-lower-check.ll Normal file
View File

@ -0,0 +1,37 @@
; RUN: opt -debug-only=irce -irce < %s 2>&1 | FileCheck %s
; CHECK: irce: loop has 1 inductive range checks:
; CHECK-NEXT: InductiveRangeCheck:
; CHECK-NEXT: Kind: RANGE_CHECK_LOWER
; CHECK-NEXT: Offset: (-1 + %n) Scale: -1 Length: (null)
; CHECK-NEXT: Branch: br i1 %abc, label %in.bounds, label %out.of.bounds
; CHECK-NEXT: irce: in function only_lower_check: constrained Loop at depth 1 containing: %loop<header><exiting>,%in.bounds<latch><exiting>
define void @only_lower_check(i32 *%arr, i32 *%a_len_ptr, i32 %n) {
entry:
%len = load i32, i32* %a_len_ptr, !range !0
%first.itr.check = icmp sgt i32 %n, 0
%start = sub i32 %n, 1
br i1 %first.itr.check, label %loop, label %exit
loop:
%idx = phi i32 [ %start, %entry ] , [ %idx.dec, %in.bounds ]
%idx.dec = sub i32 %idx, 1
%abc = icmp sge i32 %idx, 0
br i1 %abc, label %in.bounds, label %out.of.bounds, !prof !1
in.bounds:
%addr = getelementptr i32, i32* %arr, i32 %idx
store i32 0, i32* %addr
%next = icmp sgt i32 %idx.dec, -1
br i1 %next, label %loop, label %exit
out.of.bounds:
ret void
exit:
ret void
}
!0 = !{i32 0, i32 2147483647}
!1 = !{!"branch_weights", i32 64, i32 4}

37
test/Transforms/IRCE/only-upper-check.ll Normal file
View File

@ -0,0 +1,37 @@
; RUN: opt -irce -debug-only=irce %s -S 2>&1 | FileCheck %s
; CHECK: irce: loop has 1 inductive range checks:
; CHECK-NEXT:InductiveRangeCheck:
; CHECK-NEXT: Kind: RANGE_CHECK_UPPER
; CHECK-NEXT: Offset: %offset Scale: 1 Length: %len = load i32, i32* %a_len_ptr, !range !0
; CHECK-NEXT: Branch: br i1 %abc, label %in.bounds, label %out.of.bounds, !prof !1
; CHECK-NEXT: irce: in function incrementing: constrained Loop at depth 1 containing: %loop<header><exiting>,%in.bounds<latch><exiting>
define void @incrementing(i32 *%arr, i32 *%a_len_ptr, i32 %n, i32 %offset) {
entry:
%len = load i32, i32* %a_len_ptr, !range !0
%first.itr.check = icmp sgt i32 %n, 0
br i1 %first.itr.check, label %loop, label %exit
loop:
%idx = phi i32 [ 0, %entry ] , [ %idx.next, %in.bounds ]
%idx.next = add i32 %idx, 1
%array.idx = add i32 %idx, %offset
%abc = icmp slt i32 %array.idx, %len
br i1 %abc, label %in.bounds, label %out.of.bounds, !prof !1
in.bounds:
%addr = getelementptr i32, i32* %arr, i32 %array.idx
store i32 0, i32* %addr
%next = icmp slt i32 %idx.next, %n
br i1 %next, label %loop, label %exit
out.of.bounds:
ret void
exit:
ret void
}
!0 = !{i32 0, i32 2147483647}
!1 = !{!"branch_weights", i32 64, i32 4}