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[SCEV] Slightly generalize getRangeViaFactoring

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This change generalizes ScalarEvolution::getRangeViaFactoring to work
with {Ext(C?A:B),+,Ext(C?A:B)} where Ext can be a zero extend, sign
extend or truncate operation.

llvm-svn: 262978
This commit is contained in:
Sanjoy Das 2016-03-09 01:50:57 +00:00
parent ea71be934f
commit 29f43f7c7a
2 changed files with 104 additions and 25 deletions
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74
lib/Analysis/ScalarEvolution.cpp
View File

@ -4568,42 +4568,70 @@ ConstantRange ScalarEvolution::getRangeViaFactoring(const SCEV *Start,
Start = SA->getOperand(1);
}
if (!isa<SCEVUnknown>(Start) || !isa<SCEVUnknown>(Step))
// We don't have anything new to contribute in this case.
return ConstantRange(BitWidth, /* isFullSet = */ true);
// RangeOf({C?A:B,+,C?P:Q}) == RangeOf(C?{A,+,P}:{B,+,Q})
// == RangeOf({A,+,P}) union RangeOf({B,+,Q})
struct SelectPattern {
Value *Condition = nullptr;
const APInt *TrueValue = nullptr;
const APInt *FalseValue = nullptr;
APInt TrueValue;
APInt FalseValue;
explicit SelectPattern(ScalarEvolution &SE, unsigned BitWidth,
const SCEV *S) {
Optional<unsigned> CastOp;
assert(SE.getTypeSizeInBits(S->getType()) == BitWidth &&
"Should be!");
// Peel off a cast operation
if (auto *SCast = dyn_cast<SCEVCastExpr>(S)) {
CastOp = SCast->getSCEVType();
S = SCast->getOperand();
}
explicit SelectPattern(const SCEVUnknown *SU) {
using namespace llvm::PatternMatch;
if (!match(SU->getValue(),
m_Select(m_Value(Condition), m_APInt(TrueValue),
m_APInt(FalseValue)))) {
auto *SU = dyn_cast<SCEVUnknown>(S);
const APInt *TrueVal, *FalseVal;
if (!SU ||
!match(SU->getValue(), m_Select(m_Value(Condition), m_APInt(TrueVal),
m_APInt(FalseVal)))) {
Condition = nullptr;
TrueValue = FalseValue = nullptr;
return;
}
TrueValue = *TrueVal;
FalseValue = *FalseVal;
// Re-apply the cast we peeled off earlier
if (CastOp.hasValue())
switch (*CastOp) {
default:
llvm_unreachable("Unknown SCEV cast type!");
case scTruncate:
TrueValue = TrueValue.trunc(BitWidth);
FalseValue = FalseValue.trunc(BitWidth);
break;
case scZeroExtend:
TrueValue = TrueValue.zext(BitWidth);
FalseValue = FalseValue.zext(BitWidth);
break;
case scSignExtend:
TrueValue = TrueValue.sext(BitWidth);
FalseValue = FalseValue.sext(BitWidth);
break;
}
}
bool isRecognized() {
assert(((Condition && TrueValue && FalseValue) ||
(!Condition && !TrueValue && !FalseValue)) &&
"Invariant: either all three are non-null or all three are null");
return TrueValue != nullptr;
}
bool isRecognized() { return Condition != nullptr; }
};
SelectPattern StartPattern(cast<SCEVUnknown>(Start));
SelectPattern StartPattern(*this, BitWidth, Start);
if (!StartPattern.isRecognized())
return ConstantRange(BitWidth, /* isFullSet = */ true);
SelectPattern StepPattern(cast<SCEVUnknown>(Step));
SelectPattern StepPattern(*this, BitWidth, Step);
if (!StepPattern.isRecognized())
return ConstantRange(BitWidth, /* isFullSet = */ true);
@ -4622,10 +4650,10 @@ ConstantRange ScalarEvolution::getRangeViaFactoring(const SCEV *Start,
// FIXME: without the explicit `this` receiver below, MSVC errors out with
// C2352 and C2512 (otherwise it isn't needed).
const SCEV *TrueStart = this->getConstant(*StartPattern.TrueValue + Offset);
const SCEV *TrueStep = this->getConstant(*StepPattern.TrueValue);
const SCEV *FalseStart = this->getConstant(*StartPattern.FalseValue + Offset);
const SCEV *FalseStep = this->getConstant(*StepPattern.FalseValue);
const SCEV *TrueStart = this->getConstant(StartPattern.TrueValue + Offset);
const SCEV *TrueStep = this->getConstant(StepPattern.TrueValue);
const SCEV *FalseStart = this->getConstant(StartPattern.FalseValue + Offset);
const SCEV *FalseStep = this->getConstant(StepPattern.FalseValue);
ConstantRange TrueRange =
this->getRangeForAffineAR(TrueStart, TrueStep, MaxBECount, BitWidth);

55
test/Analysis/ScalarEvolution/increasing-or-decreasing-iv.ll
View File

@ -100,7 +100,7 @@ loop:
%iv.sext = sext i32 %iv to i64
%iv.next = add i32 %iv, %step
; CHECK: %iv.sext = sext i32 %iv to i64
; CHECK-NEXT: --> {(sext i32 %start to i64),+,(sext i32 %step to i64)}<nsw><%loop>
; CHECK-NEXT: --> {(sext i32 %start to i64),+,(sext i32 %step to i64)}<nsw><%loop> U: [0,128) S: [0,128)
%loop.iv.inc = add i32 %loop.iv, 1
%be.cond = icmp ne i32 %loop.iv.inc, 128
br i1 %be.cond, label %loop, label %leave
@ -128,7 +128,7 @@ loop:
%iv = phi i16 [ %start, %entry ], [ %iv.next, %loop ]
%iv.zext = zext i16 %iv to i64
; CHECK: %iv.zext = zext i16 %iv to i64
; CHECK-NEXT: --> {(zext i16 %start to i64),+,(zext i16 %step to i64)}<nuw><%loop>
; CHECK-NEXT: --> {(zext i16 %start to i64),+,(zext i16 %step to i64)}<nuw><%loop> U: [0,64644) S: [0,64644)
%iv.next = add i16 %iv, %step
%loop.iv.inc = add i16 %loop.iv, 1
%be.cond = icmp ne i16 %loop.iv.inc, 128
@ -137,3 +137,54 @@ loop:
leave:
ret void
}
define void @f4(i1 %c) {
; CHECK-LABEL: Classifying expressions for: @f4
; @f4() demonstrates a case where SCEV is not able to compute a
; precise range for %iv.trunc, though it should be able to, in theory.
; This is because SCEV looks into affine add recurrences only when the
; backedge taken count of the loop has the same bitwidth as the
; induction variable.
entry:
%start = select i1 %c, i32 127, i32 0
%step = select i1 %c, i32 -1, i32 1
br label %loop
loop:
%loop.iv = phi i32 [ 0, %entry ], [ %loop.iv.inc, %loop ]
%iv = phi i32 [ %start, %entry ], [ %iv.next, %loop ]
%iv.trunc = trunc i32 %iv to i16
; CHECK: %iv.trunc = trunc i32 %iv to i16
; CHECK-NEXT: --> {(trunc i32 %start to i16),+,(trunc i32 %step to i16)}<%loop> U: full-set S: full-set
%iv.next = add i32 %iv, %step
%loop.iv.inc = add i32 %loop.iv, 1
%be.cond = icmp ne i32 %loop.iv.inc, 128
br i1 %be.cond, label %loop, label %leave
leave:
ret void
}
define void @f5(i1 %c) {
; CHECK-LABEL: Classifying expressions for: @f5
entry:
%start = select i1 %c, i32 127, i32 0
%step = select i1 %c, i32 -1, i32 1
br label %loop
loop:
%loop.iv = phi i16 [ 0, %entry ], [ %loop.iv.inc, %loop ]
%iv = phi i32 [ %start, %entry ], [ %iv.next, %loop ]
%iv.trunc = trunc i32 %iv to i16
; CHECK: %iv.trunc = trunc i32 %iv to i16
; CHECK-NEXT: --> {(trunc i32 %start to i16),+,(trunc i32 %step to i16)}<%loop> U: [0,128) S: [0,128)
%iv.next = add i32 %iv, %step
%loop.iv.inc = add i16 %loop.iv, 1
%be.cond = icmp ne i16 %loop.iv.inc, 128
br i1 %be.cond, label %loop, label %leave
leave:
ret void
}