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Inlining often produces landingpad instructions with repeated

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catch or repeated filter clauses.  Teach instcombine a bunch
of tricks for simplifying landingpad clauses.  Currently the
code only recognizes the GNU C++ and Ada personality functions,
but that doesn't stop it doing a bunch of "generic" transforms
which are hopefully fine for any real-world personality function.
If these "generic" transforms turn out not to be generic, they
can always be conditioned on the personality function.  Probably
someone should add the ObjC++ personality function.  I didn't as
I don't know anything about it.

llvm-svn: 140852
This commit is contained in:
Duncan Sands 2011-09-30 13:12:16 +00:00
parent 774d60816b
commit b4c8b2d9fa
3 changed files with 495 additions and 0 deletions
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1
lib/Transforms/InstCombine/InstCombine.h
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@ -193,6 +193,7 @@ public:
Instruction *visitExtractElementInst(ExtractElementInst &EI);
Instruction *visitShuffleVectorInst(ShuffleVectorInst &SVI);
Instruction *visitExtractValueInst(ExtractValueInst &EV);
Instruction *visitLandingPadInst(LandingPadInst &LI);
// visitInstruction - Specify what to return for unhandled instructions...
Instruction *visitInstruction(Instruction &I) { return 0; }

337
lib/Transforms/InstCombine/InstructionCombining.cpp
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@ -49,6 +49,7 @@
#include "llvm/Support/ValueHandle.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm-c/Initialization.h"
#include <algorithm>
#include <climits>
@ -1413,6 +1414,342 @@ Instruction *InstCombiner::visitExtractValueInst(ExtractValueInst &EV) {
return 0;
}
enum Personality_Type {
Unknown_Personality,
GNU_Ada_Personality,
GNU_CXX_Personality
};
/// RecognizePersonality - See if the given exception handling personality
/// function is one that we understand. If so, return a description of it;
/// otherwise return Unknown_Personality.
static Personality_Type RecognizePersonality(Value *Pers) {
Function *F = dyn_cast<Function>(Pers->stripPointerCasts());
if (!F)
return Unknown_Personality;
return StringSwitch<Personality_Type>(F->getName())
.Case("__gnat_eh_personality", GNU_Ada_Personality)
.Case("__gxx_personality_v0", GNU_CXX_Personality)
.Default(Unknown_Personality);
}
/// isCatchAll - Return 'true' if the given typeinfo will match anything.
static bool isCatchAll(Personality_Type Personality, Constant *TypeInfo) {
switch (Personality) {
case Unknown_Personality:
return false;
case GNU_Ada_Personality:
// While __gnat_all_others_value will match any Ada exception, it doesn't
// match foreign exceptions (or didn't, before gcc-4.7).
return false;
case GNU_CXX_Personality:
return TypeInfo->isNullValue();
}
llvm_unreachable("Unknown personality!");
}
static bool shorter_filter(const Value *LHS, const Value *RHS) {
return
cast<ArrayType>(LHS->getType())->getNumElements()
<
cast<ArrayType>(RHS->getType())->getNumElements();
}
Instruction *InstCombiner::visitLandingPadInst(LandingPadInst &LI) {
// The logic here should be correct for any real-world personality function.
// However if that turns out not to be true, the offending logic can always
// be conditioned on the personality function, like the catch-all logic is.
Personality_Type Personality = RecognizePersonality(LI.getPersonalityFn());
// Simplify the list of clauses, eg by removing repeated catch clauses
// (these are often created by inlining).
bool MakeNewInstruction = false; // If true, recreate using the following:
SmallVector<Value *, 16> NewClauses; // - Clauses for the new instruction;
bool CleanupFlag = LI.isCleanup(); // - The new instruction is a cleanup.
SmallPtrSet<Value *, 16> AlreadyCaught; // Typeinfos known caught already.
for (unsigned i = 0, e = LI.getNumClauses(); i != e; ++i) {
bool isLastClause = i + 1 == e;
if (LI.isCatch(i)) {
// A catch clause.
Value *CatchClause = LI.getClause(i);
Constant *TypeInfo = cast<Constant>(CatchClause->stripPointerCasts());
// If we already saw this clause, there is no point in having a second
// copy of it.
if (AlreadyCaught.insert(TypeInfo)) {
// This catch clause was not already seen.
NewClauses.push_back(CatchClause);
} else {
// Repeated catch clause - drop the redundant copy.
MakeNewInstruction = true;
}
// If this is a catch-all then there is no point in keeping any following
// clauses or marking the landingpad as having a cleanup.
if (isCatchAll(Personality, TypeInfo)) {
if (!isLastClause)
MakeNewInstruction = true;
CleanupFlag = false;
break;
}
} else {
// A filter clause. If any of the filter elements were already caught
// then they can be dropped from the filter. It is tempting to try to
// exploit the filter further by saying that any typeinfo that does not
// occur in the filter can't be caught later (and thus can be dropped).
// However this would be wrong, since typeinfos can match without being
// equal (for example if one represents a C++ class, and the other some
// class derived from it).
assert(LI.isFilter(i) && "Unsupported landingpad clause!");
Value *FilterClause = LI.getClause(i);
ArrayType *FilterType = cast<ArrayType>(FilterClause->getType());
unsigned NumTypeInfos = FilterType->getNumElements();
// An empty filter catches everything, so there is no point in keeping any
// following clauses or marking the landingpad as having a cleanup. By
// dealing with this case here the following code is made a bit simpler.
if (!NumTypeInfos) {
NewClauses.push_back(FilterClause);
if (!isLastClause)
MakeNewInstruction = true;
CleanupFlag = false;
break;
}
bool MakeNewFilter = false; // If true, make a new filter.
SmallVector<Constant *, 16> NewFilterElts; // New elements.
if (isa<ConstantAggregateZero>(FilterClause)) {
// Not an empty filter - it contains at least one null typeinfo.
assert(NumTypeInfos > 0 && "Should have handled empty filter already!");
Constant *TypeInfo =
Constant::getNullValue(FilterType->getElementType());
// If this typeinfo is a catch-all then the filter can never match.
if (isCatchAll(Personality, TypeInfo)) {
// Throw the filter away.
MakeNewInstruction = true;
continue;
}
// There is no point in having multiple copies of this typeinfo, so
// discard all but the first copy if there is more than one.
NewFilterElts.push_back(TypeInfo);
if (NumTypeInfos > 1)
MakeNewFilter = true;
} else {
ConstantArray *Filter = cast<ConstantArray>(FilterClause);
SmallPtrSet<Value *, 16> SeenInFilter; // For uniquing the elements.
NewFilterElts.reserve(NumTypeInfos);
// Remove any filter elements that were already caught or that already
// occurred in the filter. While there, see if any of the elements are
// catch-alls. If so, the filter can be discarded.
bool SawCatchAll = false;
for (unsigned j = 0; j != NumTypeInfos; ++j) {
Value *Elt = Filter->getOperand(j);
Constant *TypeInfo = cast<Constant>(Elt->stripPointerCasts());
if (isCatchAll(Personality, TypeInfo)) {
// This element is a catch-all. Bail out, noting this fact.
SawCatchAll = true;
break;
}
if (AlreadyCaught.count(TypeInfo))
// Already caught by an earlier clause, so having it in the filter
// is pointless.
continue;
// There is no point in having multiple copies of the same typeinfo in
// a filter, so only add it if we didn't already.
if (SeenInFilter.insert(TypeInfo))
NewFilterElts.push_back(cast<Constant>(Elt));
}
// A filter containing a catch-all cannot match anything by definition.
if (SawCatchAll) {
// Throw the filter away.
MakeNewInstruction = true;
continue;
}
// If we dropped something from the filter, make a new one.
if (NewFilterElts.size() < NumTypeInfos)
MakeNewFilter = true;
}
if (MakeNewFilter) {
FilterType = ArrayType::get(FilterType->getElementType(),
NewFilterElts.size());
FilterClause = ConstantArray::get(FilterType, NewFilterElts);
MakeNewInstruction = true;
}
NewClauses.push_back(FilterClause);
// If the new filter is empty then it will catch everything so there is
// no point in keeping any following clauses or marking the landingpad
// as having a cleanup. The case of the original filter being empty was
// already handled above.
if (MakeNewFilter && !NewFilterElts.size()) {
assert(MakeNewInstruction && "New filter but not a new instruction!");
CleanupFlag = false;
break;
}
}
}
// If several filters occur in a row then reorder them so that the shortest
// filters come first (those with the smallest number of elements). This is
// advantageous because shorter filters are more likely to match, speeding up
// unwinding, but mostly because it increases the effectiveness of the other
// filter optimizations below.
for (unsigned i = 0, e = NewClauses.size(); i + 1 < e; ) {
unsigned j;
// Find the maximal 'j' s.t. the range [i, j) consists entirely of filters.
for (j = i; j != e; ++j)
if (!isa<ArrayType>(NewClauses[j]->getType()))
break;
// Check whether the filters are already sorted by length. We need to know
// if sorting them is actually going to do anything so that we only make a
// new landingpad instruction if it does.
for (unsigned k = i; k + 1 < j; ++k)
if (shorter_filter(NewClauses[k+1], NewClauses[k])) {
// Not sorted, so sort the filters now. Doing an unstable sort would be
// correct too but reordering filters pointlessly might confuse users.
std::stable_sort(NewClauses.begin() + i, NewClauses.begin() + j,
shorter_filter);
MakeNewInstruction = true;
break;
}
// Look for the next batch of filters.
i = j + 1;
}
// If typeinfos matched if and only if equal, then the elements of a filter L
// that occurs later than a filter F could be replaced by the intersection of
// the elements of F and L. In reality two typeinfos can match without being
// equal (for example if one represents a C++ class, and the other some class
// derived from it) so it would be wrong to perform this transform in general.
// However the transform is correct and useful if F is a subset of L. In that
// case L can be replaced by F, and thus removed altogether since repeating a
// filter is pointless. So here we look at all pairs of filters F and L where
// L follows F in the list of clauses, and remove L if every element of F is
// an element of L. This can occur when inlining C++ functions with exception
// specifications.
for (unsigned i = 0; i + 1 < NewClauses.size(); ++i) {
// Examine each filter in turn.
Value *Filter = NewClauses[i];
ArrayType *FTy = dyn_cast<ArrayType>(Filter->getType());
if (!FTy)
// Not a filter - skip it.
continue;
unsigned FElts = FTy->getNumElements();
// Examine each filter following this one. Doing this backwards means that
// we don't have to worry about filters disappearing under us when removed.
for (unsigned j = NewClauses.size() - 1; j != i; --j) {
Value *LFilter = NewClauses[j];
ArrayType *LTy = dyn_cast<ArrayType>(LFilter->getType());
if (!LTy)
// Not a filter - skip it.
continue;
// If Filter is a subset of LFilter, i.e. every element of Filter is also
// an element of LFilter, then discard LFilter.
SmallVector<Value *, 16>::iterator J = NewClauses.begin() + j;
// If Filter is empty then it is a subset of LFilter.
if (!FElts) {
// Discard LFilter.
NewClauses.erase(J);
MakeNewInstruction = true;
// Move on to the next filter.
continue;
}
unsigned LElts = LTy->getNumElements();
// If Filter is longer than LFilter then it cannot be a subset of it.
if (FElts > LElts)
// Move on to the next filter.
continue;
// At this point we know that LFilter has at least one element.
if (isa<ConstantAggregateZero>(LFilter)) { // LFilter only contains zeros.
// Filter is a subset of LFilter iff Filter contains only zeros (as we
// already know that Filter is not longer than LFilter).
if (isa<ConstantAggregateZero>(Filter)) {
assert(FElts <= LElts && "Should have handled this case earlier!");
// Discard LFilter.
NewClauses.erase(J);
MakeNewInstruction = true;
}
// Move on to the next filter.
continue;
}
ConstantArray *LArray = cast<ConstantArray>(LFilter);
if (isa<ConstantAggregateZero>(Filter)) { // Filter only contains zeros.
// Since Filter is non-empty and contains only zeros, it is a subset of
// LFilter iff LFilter contains a zero.
assert(FElts > 0 && "Should have eliminated the empty filter earlier!");
for (unsigned l = 0; l != LElts; ++l)
if (LArray->getOperand(l)->isNullValue()) {
// LFilter contains a zero - discard it.
NewClauses.erase(J);
MakeNewInstruction = true;
break;
}
// Move on to the next filter.
continue;
}
// At this point we know that both filters are ConstantArrays. Loop over
// operands to see whether every element of Filter is also an element of
// LFilter. Since filters tend to be short this is probably faster than
// using a method that scales nicely.
ConstantArray *FArray = cast<ConstantArray>(Filter);
bool AllFound = true;
for (unsigned f = 0; f != FElts; ++f) {
Value *FTypeInfo = FArray->getOperand(f)->stripPointerCasts();
AllFound = false;
for (unsigned l = 0; l != LElts; ++l) {
Value *LTypeInfo = LArray->getOperand(l)->stripPointerCasts();
if (LTypeInfo == FTypeInfo) {
AllFound = true;
break;
}
}
if (!AllFound)
break;
}
if (AllFound) {
// Discard LFilter.
NewClauses.erase(J);
MakeNewInstruction = true;
}
// Move on to the next filter.
}
}
// If we changed any of the clauses, replace the old landingpad instruction
// with a new one.
if (MakeNewInstruction) {
LandingPadInst *NLI = LandingPadInst::Create(LI.getType(),
LI.getPersonalityFn(),
NewClauses.size());
for (unsigned i = 0, e = NewClauses.size(); i != e; ++i)
NLI->addClause(NewClauses[i]);
// A landing pad with no clauses must have the cleanup flag set. It is
// theoretically possible, though highly unlikely, that we eliminated all
// clauses. If so, force the cleanup flag to true.
if (NewClauses.empty())
CleanupFlag = true;
NLI->setCleanup(CleanupFlag);
return NLI;
}
// Even if none of the clauses changed, we may nonetheless have understood
// that the cleanup flag is pointless. Clear it if so.
if (LI.isCleanup() != CleanupFlag) {
assert(!CleanupFlag && "Adding a cleanup, not removing one?!");
LI.setCleanup(CleanupFlag);
return &LI;
}
return 0;
}

157
test/Transforms/InstCombine/LandingPadClauses.ll Normal file
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@ -0,0 +1,157 @@
; RUN: opt < %s -instcombine -S | FileCheck %s
@T1 = external constant i32
@T2 = external constant i32
@T3 = external constant i32
declare i32 @generic_personality(i32, i64, i8*, i8*)
declare i32 @__gxx_personality_v0(i32, i64, i8*, i8*)
declare void @bar()
define void @foo_generic() {
; CHECK: @foo_generic
invoke void @bar()
to label %cont.a unwind label %lpad.a
cont.a:
invoke void @bar()
to label %cont.b unwind label %lpad.b
cont.b:
invoke void @bar()
to label %cont.c unwind label %lpad.c
cont.c:
invoke void @bar()
to label %cont.d unwind label %lpad.d
cont.d:
invoke void @bar()
to label %cont.e unwind label %lpad.e
cont.e:
invoke void @bar()
to label %cont.f unwind label %lpad.f
cont.f:
invoke void @bar()
to label %cont.g unwind label %lpad.g
cont.g:
invoke void @bar()
to label %cont.h unwind label %lpad.h
cont.h:
ret void
lpad.a:
%a = landingpad { i8*, i32 } personality i32 (i32, i64, i8*, i8*)* @generic_personality
catch i32* @T1
catch i32* @T2
catch i32* @T1
catch i32* @T2
unreachable
; CHECK: %a = landingpad
; CHECK-NEXT: @T1
; CHECK-NEXT: @T2
; CHECK-NEXT: unreachable
lpad.b:
%b = landingpad { i8*, i32 } personality i32 (i32, i64, i8*, i8*)* @generic_personality
filter [0 x i32*] zeroinitializer
catch i32* @T1
unreachable
; CHECK: %b = landingpad
; CHECK-NEXT: filter
; CHECK-NEXT: unreachable
lpad.c:
%c = landingpad { i8*, i32 } personality i32 (i32, i64, i8*, i8*)* @generic_personality
catch i32* @T1
filter [1 x i32*] [i32* @T1]
catch i32* @T2
unreachable
; CHECK: %c = landingpad
; CHECK-NEXT: @T1
; CHECK-NEXT: filter [0 x i32*]
; CHECK-NEXT: unreachable
lpad.d:
%d = landingpad { i8*, i32 } personality i32 (i32, i64, i8*, i8*)* @generic_personality
filter [3 x i32*] zeroinitializer
unreachable
; CHECK: %d = landingpad
; CHECK-NEXT: filter [1 x i32*] zeroinitializer
; CHECK-NEXT: unreachable
lpad.e:
%e = landingpad { i8*, i32 } personality i32 (i32, i64, i8*, i8*)* @generic_personality
catch i32* @T1
filter [3 x i32*] [i32* @T1, i32* @T2, i32* @T2]
unreachable
; CHECK: %e = landingpad
; CHECK-NEXT: @T1
; CHECK-NEXT: filter [1 x i32*] [i32* @T2]
; CHECK-NEXT: unreachable
lpad.f:
%f = landingpad { i8*, i32 } personality i32 (i32, i64, i8*, i8*)* @generic_personality
filter [2 x i32*] [i32* @T2, i32* @T1]
filter [1 x i32*] [i32* @T1]
unreachable
; CHECK: %f = landingpad
; CHECK-NEXT: filter [1 x i32*] [i32* @T1]
; CHECK-NEXT: unreachable
lpad.g:
%g = landingpad { i8*, i32 } personality i32 (i32, i64, i8*, i8*)* @generic_personality
filter [1 x i32*] [i32* @T1]
catch i32* @T3
filter [2 x i32*] [i32* @T2, i32* @T1]
unreachable
; CHECK: %g = landingpad
; CHECK-NEXT: filter [1 x i32*] [i32* @T1]
; CHECK-NEXT: catch i32* @T3
; CHECK-NEXT: unreachable
lpad.h:
%h = landingpad { i8*, i32 } personality i32 (i32, i64, i8*, i8*)* @generic_personality
filter [2 x i32*] [i32* @T1, i32* null]
filter [1 x i32*] zeroinitializer
unreachable
; CHECK: %h = landingpad
; CHECK-NEXT: filter [1 x i32*] zeroinitializer
; CHECK-NEXT: unreachable
}
define void @foo_cxx() {
; CHECK: @foo_cxx
invoke void @bar()
to label %cont.a unwind label %lpad.a
cont.a:
invoke void @bar()
to label %cont.b unwind label %lpad.b
cont.b:
invoke void @bar()
to label %cont.c unwind label %lpad.c
cont.c:
ret void
lpad.a:
%a = landingpad { i8*, i32 } personality i32 (i32, i64, i8*, i8*)* @__gxx_personality_v0
catch i32* null
catch i32* @T1
unreachable
; CHECK: %a = landingpad
; CHECK-NEXT: null
; CHECK-NEXT: unreachable
lpad.b:
%b = landingpad { i8*, i32 } personality i32 (i32, i64, i8*, i8*)* @__gxx_personality_v0
filter [1 x i32*] zeroinitializer
unreachable
; CHECK: %b = landingpad
; CHECK-NEXT: cleanup
; CHECK-NEXT: unreachable
lpad.c:
%c = landingpad { i8*, i32 } personality i32 (i32, i64, i8*, i8*)* @__gxx_personality_v0
filter [2 x i32*] [i32* @T1, i32* null]
unreachable
; CHECK: %c = landingpad
; CHECK-NEXT: cleanup
; CHECK-NEXT: unreachable
}