aboutsummaryrefslogtreecommitdiff
path: root/llvm/lib/Transforms/IPO
diff options
context:
space:
mode:
Diffstat (limited to 'llvm/lib/Transforms/IPO')
-rw-r--r--llvm/lib/Transforms/IPO/LowerTypeTests.cpp2
-rw-r--r--llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp109
2 files changed, 77 insertions, 34 deletions
diff --git a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
index 46fb567..aa1346d 100644
--- a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
+++ b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
@@ -1271,7 +1271,7 @@ bool LowerTypeTestsModule::hasBranchTargetEnforcement() {
// the module flags.
if (const auto *BTE = mdconst::extract_or_null<ConstantInt>(
M.getModuleFlag("branch-target-enforcement")))
- HasBranchTargetEnforcement = (BTE->getZExtValue() != 0);
+ HasBranchTargetEnforcement = !BTE->isZero();
else
HasBranchTargetEnforcement = 0;
}
diff --git a/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp b/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
index 76e588b..2dd0fde 100644
--- a/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
+++ b/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
@@ -24,7 +24,8 @@
// returns 0, or a single vtable's function returns 1, replace each virtual
// call with a comparison of the vptr against that vtable's address.
//
-// This pass is intended to be used during the regular and thin LTO pipelines:
+// This pass is intended to be used during the regular/thin and non-LTO
+// pipelines:
//
// During regular LTO, the pass determines the best optimization for each
// virtual call and applies the resolutions directly to virtual calls that are
@@ -48,6 +49,14 @@
// is supported.
// - Import phase: (same as with hybrid case above).
//
+// During Speculative devirtualization mode -not restricted to LTO-:
+// - The pass applies speculative devirtualization without requiring any type of
+// visibility.
+// - Skips other features like virtual constant propagation, uniform return
+// value optimization, unique return value optimization and branch funnels as
+// they need LTO.
+// - This mode is enabled via 'devirtualize-speculatively' flag.
+//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/IPO/WholeProgramDevirt.h"
@@ -61,7 +70,9 @@
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/BasicAliasAnalysis.h"
#include "llvm/Analysis/BlockFrequencyInfo.h"
+#include "llvm/Analysis/ModuleSummaryAnalysis.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
+#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/Analysis/TypeMetadataUtils.h"
#include "llvm/Bitcode/BitcodeReader.h"
#include "llvm/Bitcode/BitcodeWriter.h"
@@ -145,6 +156,13 @@ static cl::opt<std::string> ClWriteSummary(
"bitcode, otherwise YAML"),
cl::Hidden);
+// TODO: This option eventually should support any public visibility vtables
+// with/out LTO.
+static cl::opt<bool> ClDevirtualizeSpeculatively(
+ "devirtualize-speculatively",
+ cl::desc("Enable speculative devirtualization optimization"),
+ cl::init(false));
+
static cl::opt<unsigned>
ClThreshold("wholeprogramdevirt-branch-funnel-threshold", cl::Hidden,
cl::init(10),
@@ -892,6 +910,8 @@ void llvm::updatePublicTypeTestCalls(Module &M,
CI->eraseFromParent();
}
} else {
+ // TODO: Don't replace public type tests when speculative devirtualization
+ // gets enabled in LTO mode.
auto *True = ConstantInt::getTrue(M.getContext());
for (Use &U : make_early_inc_range(PublicTypeTestFunc->uses())) {
auto *CI = cast<CallInst>(U.getUser());
@@ -928,17 +948,17 @@ void llvm::updateVCallVisibilityInIndex(
// linker, as we have no information on their eventual use.
if (DynamicExportSymbols.count(P.first))
continue;
+ // With validation enabled, we want to exclude symbols visible to regular
+ // objects. Local symbols will be in this group due to the current
+ // implementation but those with VCallVisibilityTranslationUnit will have
+ // already been marked in clang so are unaffected.
+ if (VisibleToRegularObjSymbols.count(P.first))
+ continue;
for (auto &S : P.second.getSummaryList()) {
auto *GVar = dyn_cast<GlobalVarSummary>(S.get());
if (!GVar ||
GVar->getVCallVisibility() != GlobalObject::VCallVisibilityPublic)
continue;
- // With validation enabled, we want to exclude symbols visible to regular
- // objects. Local symbols will be in this group due to the current
- // implementation but those with VCallVisibilityTranslationUnit will have
- // already been marked in clang so are unaffected.
- if (VisibleToRegularObjSymbols.count(P.first))
- continue;
GVar->setVCallVisibility(GlobalObject::VCallVisibilityLinkageUnit);
}
}
@@ -1083,10 +1103,10 @@ bool DevirtModule::tryFindVirtualCallTargets(
if (!TM.Bits->GV->isConstant())
return false;
- // We cannot perform whole program devirtualization analysis on a vtable
- // with public LTO visibility.
- if (TM.Bits->GV->getVCallVisibility() ==
- GlobalObject::VCallVisibilityPublic)
+ // Without ClDevirtualizeSpeculatively, we cannot perform whole program
+ // devirtualization analysis on a vtable with public LTO visibility.
+ if (!ClDevirtualizeSpeculatively && TM.Bits->GV->getVCallVisibility() ==
+ GlobalObject::VCallVisibilityPublic)
return false;
Function *Fn = nullptr;
@@ -1105,6 +1125,12 @@ bool DevirtModule::tryFindVirtualCallTargets(
if (Fn->getName() == "__cxa_pure_virtual")
continue;
+ // In most cases empty functions will be overridden by the
+ // implementation of the derived class, so we can skip them.
+ if (ClDevirtualizeSpeculatively && Fn->getReturnType()->isVoidTy() &&
+ Fn->getInstructionCount() <= 1)
+ continue;
+
// We can disregard unreachable functions as possible call targets, as
// unreachable functions shouldn't be called.
if (mustBeUnreachableFunction(Fn, ExportSummary))
@@ -1135,14 +1161,10 @@ bool DevirtIndex::tryFindVirtualCallTargets(
// and therefore the same GUID. This can happen if there isn't enough
// distinguishing path when compiling the source file. In that case we
// conservatively return false early.
+ if (P.VTableVI.hasLocal() && P.VTableVI.getSummaryList().size() > 1)
+ return false;
const GlobalVarSummary *VS = nullptr;
- bool LocalFound = false;
for (const auto &S : P.VTableVI.getSummaryList()) {
- if (GlobalValue::isLocalLinkage(S->linkage())) {
- if (LocalFound)
- return false;
- LocalFound = true;
- }
auto *CurVS = cast<GlobalVarSummary>(S->getBaseObject());
if (!CurVS->vTableFuncs().empty() ||
// Previously clang did not attach the necessary type metadata to
@@ -1158,6 +1180,7 @@ bool DevirtIndex::tryFindVirtualCallTargets(
// with public LTO visibility.
if (VS->getVCallVisibility() == GlobalObject::VCallVisibilityPublic)
return false;
+ break;
}
}
// There will be no VS if all copies are available_externally having no
@@ -1223,10 +1246,12 @@ void DevirtModule::applySingleImplDevirt(VTableSlotInfo &SlotInfo,
CallTrap->setDebugLoc(CB.getDebugLoc());
}
- // If fallback checking is enabled, add support to compare the virtual
- // function pointer to the devirtualized target. In case of a mismatch,
- // fall back to indirect call.
- if (DevirtCheckMode == WPDCheckMode::Fallback) {
+ // If fallback checking or speculative devirtualization are enabled,
+ // add support to compare the virtual function pointer to the
+ // devirtualized target. In case of a mismatch, fall back to indirect
+ // call.
+ if (DevirtCheckMode == WPDCheckMode::Fallback ||
+ ClDevirtualizeSpeculatively) {
MDNode *Weights = MDBuilder(M.getContext()).createLikelyBranchWeights();
// Version the indirect call site. If the called value is equal to the
// given callee, 'NewInst' will be executed, otherwise the original call
@@ -1383,9 +1408,8 @@ bool DevirtIndex::trySingleImplDevirt(MutableArrayRef<ValueInfo> TargetsForSlot,
// If the summary list contains multiple summaries where at least one is
// a local, give up, as we won't know which (possibly promoted) name to use.
- for (const auto &S : TheFn.getSummaryList())
- if (GlobalValue::isLocalLinkage(S->linkage()) && Size > 1)
- return false;
+ if (TheFn.hasLocal() && Size > 1)
+ return false;
// Collect functions devirtualized at least for one call site for stats.
if (PrintSummaryDevirt || AreStatisticsEnabled())
@@ -2057,15 +2081,15 @@ void DevirtModule::scanTypeTestUsers(
Function *TypeTestFunc,
DenseMap<Metadata *, std::set<TypeMemberInfo>> &TypeIdMap) {
// Find all virtual calls via a virtual table pointer %p under an assumption
- // of the form llvm.assume(llvm.type.test(%p, %md)). This indicates that %p
- // points to a member of the type identifier %md. Group calls by (type ID,
- // offset) pair (effectively the identity of the virtual function) and store
- // to CallSlots.
+ // of the form llvm.assume(llvm.type.test(%p, %md)) or
+ // llvm.assume(llvm.public.type.test(%p, %md)).
+ // This indicates that %p points to a member of the type identifier %md.
+ // Group calls by (type ID, offset) pair (effectively the identity of the
+ // virtual function) and store to CallSlots.
for (Use &U : llvm::make_early_inc_range(TypeTestFunc->uses())) {
auto *CI = dyn_cast<CallInst>(U.getUser());
if (!CI)
continue;
-
// Search for virtual calls based on %p and add them to DevirtCalls.
SmallVector<DevirtCallSite, 1> DevirtCalls;
SmallVector<CallInst *, 1> Assumes;
@@ -2348,6 +2372,12 @@ bool DevirtModule::run() {
(ImportSummary && ImportSummary->partiallySplitLTOUnits()))
return false;
+ Function *PublicTypeTestFunc = nullptr;
+ // If we are in speculative devirtualization mode, we can work on the public
+ // type test intrinsics.
+ if (ClDevirtualizeSpeculatively)
+ PublicTypeTestFunc =
+ Intrinsic::getDeclarationIfExists(&M, Intrinsic::public_type_test);
Function *TypeTestFunc =
Intrinsic::getDeclarationIfExists(&M, Intrinsic::type_test);
Function *TypeCheckedLoadFunc =
@@ -2361,8 +2391,9 @@ bool DevirtModule::run() {
// module, this pass has nothing to do. But if we are exporting, we also need
// to handle any users that appear only in the function summaries.
if (!ExportSummary &&
- (!TypeTestFunc || TypeTestFunc->use_empty() || !AssumeFunc ||
- AssumeFunc->use_empty()) &&
+ (((!PublicTypeTestFunc || PublicTypeTestFunc->use_empty()) &&
+ (!TypeTestFunc || TypeTestFunc->use_empty())) ||
+ !AssumeFunc || AssumeFunc->use_empty()) &&
(!TypeCheckedLoadFunc || TypeCheckedLoadFunc->use_empty()) &&
(!TypeCheckedLoadRelativeFunc ||
TypeCheckedLoadRelativeFunc->use_empty()))
@@ -2373,6 +2404,9 @@ bool DevirtModule::run() {
DenseMap<Metadata *, std::set<TypeMemberInfo>> TypeIdMap;
buildTypeIdentifierMap(Bits, TypeIdMap);
+ if (PublicTypeTestFunc && AssumeFunc)
+ scanTypeTestUsers(PublicTypeTestFunc, TypeIdMap);
+
if (TypeTestFunc && AssumeFunc)
scanTypeTestUsers(TypeTestFunc, TypeIdMap);
@@ -2472,8 +2506,12 @@ bool DevirtModule::run() {
.WPDRes[S.first.ByteOffset];
if (tryFindVirtualCallTargets(TargetsForSlot, TypeMemberInfos,
S.first.ByteOffset, ExportSummary)) {
-
- if (!trySingleImplDevirt(ExportSummary, TargetsForSlot, S.second, Res)) {
+ bool SingleImplDevirt =
+ trySingleImplDevirt(ExportSummary, TargetsForSlot, S.second, Res);
+ // Out of speculative devirtualization mode, Try to apply virtual constant
+ // propagation or branch funneling.
+ // TODO: This should eventually be enabled for non-public type tests.
+ if (!SingleImplDevirt && !ClDevirtualizeSpeculatively) {
DidVirtualConstProp |=
tryVirtualConstProp(TargetsForSlot, S.second, Res, S.first);
@@ -2549,6 +2587,11 @@ void DevirtIndex::run() {
if (ExportSummary.typeIdCompatibleVtableMap().empty())
return;
+ // Assert that we haven't made any changes that would affect the hasLocal()
+ // flag on the GUID summary info.
+ assert(!ExportSummary.withInternalizeAndPromote() &&
+ "Expect index-based WPD to run before internalization and promotion");
+
DenseMap<GlobalValue::GUID, std::vector<StringRef>> NameByGUID;
for (const auto &P : ExportSummary.typeIdCompatibleVtableMap()) {
NameByGUID[GlobalValue::getGUIDAssumingExternalLinkage(P.first)].push_back(
generated by cgit v1.1 at 2025-10-23 21:51:49 +0000