WholeProgramDevirt.cpp File Reference (original) (raw)

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Namespaces
namespace	llvm
	This is an optimization pass for GlobalISel generic memory operations.

Macros
#define	DEBUG_TYPE "wholeprogramdevirt"

Enumerations
enum	WPDCheckMode { None, Trap, Fallback }
	Mechanism to add runtime checking of devirtualization decisions, optionally trapping or falling back to indirect call on any that are not correct. More...

Functions
	STATISTIC (NumDevirtTargets, "Number of whole program devirtualization targets")
	STATISTIC (NumSingleImpl, "Number of single implementation devirtualizations")
	STATISTIC (NumBranchFunnel, "Number of branch funnels")
	STATISTIC (NumUniformRetVal, "Number of uniform return value optimizations")
	STATISTIC (NumUniqueRetVal, "Number of unique return value optimizations")
	STATISTIC (NumVirtConstProp1Bit, "Number of 1 bit virtual constant propagations")
	STATISTIC (NumVirtConstProp, "Number of virtual constant propagations")
	DEBUG_COUNTER (CallsToDevirt, "calls-to-devirt", "Controls how many calls should be devirtualized.")
static bool	mustBeUnreachableFunction (ValueInfo TheFnVI)
static bool	typeIDVisibleToRegularObj (StringRef TypeID, function_ref< bool(StringRef)> IsVisibleToRegularObj)
static bool	skipUpdateDueToValidation (GlobalVariable &GV, function_ref< bool(StringRef)> IsVisibleToRegularObj)
static Error	checkCombinedSummaryForTesting (ModuleSummaryIndex *Summary)
static bool	addCalls (VTableSlotInfo &SlotInfo, const ValueInfo &Callee)

Variables
static cl::opt< PassSummaryAction >	llvm::ClSummaryAction ("wholeprogramdevirt-summary-action", cl::desc("What to do with the summary when running this pass"), cl::values(clEnumValN(PassSummaryAction::None, "none", "Do nothing"), clEnumValN(PassSummaryAction::Import, "import", "Import typeid resolutions from summary and globals"), clEnumValN(PassSummaryAction::Export, "export", "Export typeid resolutions to summary and globals")), cl::Hidden)
static cl::opt< std::string >	llvm::ClReadSummary ("wholeprogramdevirt-read-summary", cl::desc("Read summary from given bitcode or YAML file before running pass"), cl::Hidden)
static cl::opt< std::string >	llvm::ClWriteSummary ("wholeprogramdevirt-write-summary", cl::desc("Write summary to given bitcode or YAML file after running pass. " "Output file format is deduced from extension: *.bc means writing " "bitcode, otherwise YAML"), cl::Hidden)
static cl::opt< bool >	llvm::ClDevirtualizeSpeculatively ("devirtualize-speculatively", cl::desc("Enable speculative devirtualization optimization"), cl::init(false))
static cl::opt< unsigned >	llvm::ClThreshold ("wholeprogramdevirt-branch-funnel-threshold", cl::Hidden, cl::init(10), cl::desc("Maximum number of call targets per " "call site to enable branch funnels"))
static cl::opt< bool >	llvm::PrintSummaryDevirt ("wholeprogramdevirt-print-index-based", cl::Hidden, cl::desc("Print index-based devirtualization messages"))
static cl::opt< bool >	llvm::WholeProgramVisibility ("whole-program-visibility", cl::Hidden, cl::desc("Enable whole program visibility"))
	Provide a way to force enable whole program visibility in tests.
static cl::opt< bool >	llvm::DisableWholeProgramVisibility ("disable-whole-program-visibility", cl::Hidden, cl::desc("Disable whole program visibility (overrides enabling options)"))
	Provide a way to force disable whole program for debugging or workarounds, when enabled via the linker.
static cl::list< std::string >	llvm::SkipFunctionNames ("wholeprogramdevirt-skip", cl::desc("Prevent function(s) from being devirtualized"), cl::Hidden, cl::CommaSeparated)
	Provide way to prevent certain function from being devirtualized.
static cl::opt< bool >	WholeProgramDevirtKeepUnreachableFunction ("wholeprogramdevirt-keep-unreachable-function", cl::desc("Regard unreachable functions as possible devirtualize targets."), cl::Hidden, cl::init(true))
	With Clang, a pure virtual class's deleting destructor is emitted as a llvm.trap intrinsic followed by an unreachable IR instruction.
static cl::opt< WPDCheckMode >	DevirtCheckMode ("wholeprogramdevirt-check", cl::Hidden, cl::desc("Type of checking for incorrect devirtualizations"), cl::values(clEnumValN(WPDCheckMode::None, "none", "No checking"), clEnumValN(WPDCheckMode::Trap, "trap", "Trap when incorrect"), clEnumValN(WPDCheckMode::Fallback, "fallback", "Fallback to indirect when incorrect")))

◆ DEBUG_TYPE

#define DEBUG_TYPE "wholeprogramdevirt"

◆ WPDCheckMode

Mechanism to add runtime checking of devirtualization decisions, optionally trapping or falling back to indirect call on any that are not correct.

Trapping mode is useful for debugging undefined behavior leading to failures with WPD. Fallback mode is useful for ensuring safety when whole program visibility may be compromised.

Enumerator
None
Trap
Fallback

Definition at line 230 of file WholeProgramDevirt.cpp.

◆ addCalls()

◆ checkCombinedSummaryForTesting()

◆ DEBUG_COUNTER()

DEBUG_COUNTER	(	CallsToDevirt	,
"calls-to-devirt"	,
"Controls how many calls should be devirtualized."	)

◆ mustBeUnreachableFunction()

◆ skipUpdateDueToValidation()

◆ STATISTIC() [1/7]

STATISTIC	(	NumBranchFunnel	,
"Number of branch funnels"	)

◆ STATISTIC() [2/7]

STATISTIC	(	NumDevirtTargets	,
"Number of whole program devirtualization targets"	)

◆ STATISTIC() [3/7]

STATISTIC	(	NumSingleImpl	,
"Number of single implementation devirtualizations"	)

◆ STATISTIC() [4/7]

STATISTIC	(	NumUniformRetVal	,
"Number of uniform return value optimizations"	)

◆ STATISTIC() [5/7]

STATISTIC	(	NumUniqueRetVal	,
"Number of unique return value optimizations"	)

◆ STATISTIC() [6/7]

STATISTIC	(	NumVirtConstProp	,
"Number of virtual constant propagations"	)

◆ STATISTIC() [7/7]

STATISTIC	(	NumVirtConstProp1Bit	,
"Number of 1 bit virtual constant propagations"	)

◆ typeIDVisibleToRegularObj()

◆ DevirtCheckMode

cl::opt< WPDCheckMode > DevirtCheckMode("wholeprogramdevirt-check", cl::Hidden, cl::desc("Type of checking for incorrect devirtualizations"), cl::values(clEnumValN(WPDCheckMode::None, "none", "No checking"), clEnumValN(WPDCheckMode::Trap, "trap", "Trap when incorrect"), clEnumValN(WPDCheckMode::Fallback, "fallback", "Fallback to indirect when incorrect"))) ( "wholeprogramdevirt-check" , cl::Hidden , cl::desc("Type of checking for incorrect devirtualizations") , cl::values(clEnumValN(WPDCheckMode::None, "none", "No checking"), clEnumValN(WPDCheckMode::Trap, "trap", "Trap when incorrect"), clEnumValN(WPDCheckMode::Fallback, "fallback", "Fallback to indirect when incorrect")) )

static

◆ WholeProgramDevirtKeepUnreachableFunction

cl::opt< bool > WholeProgramDevirtKeepUnreachableFunction("wholeprogramdevirt-keep-unreachable-function", cl::desc("Regard unreachable functions as possible devirtualize targets."), cl::Hidden, cl::init(true)) ( "wholeprogramdevirt-keep-unreachable-function" , cl::desc("Regard unreachable functions as possible devirtualize targets.") , cl::Hidden , cl::init(true) )	static

With Clang, a pure virtual class's deleting destructor is emitted as a llvm.trap intrinsic followed by an unreachable IR instruction.

In the context of whole program devirtualization, the deleting destructor of a pure virtual class won't be invoked by the source code so safe to skip as a devirtualize target.

However, not all unreachable functions are safe to skip. In some cases, the program intends to run such functions and terminate, for instance, a unit test may run a death test. A non-test program might (or allowed to) invoke such functions to report failures (whether/when it's a good practice or not is a different topic).

This option is enabled to keep an unreachable function as a possible devirtualize target to conservatively keep the program behavior.

TODO: Make a pure virtual class's deleting destructor precisely identifiable in Clang's codegen for more devirtualization in LLVM.

Referenced by mustBeUnreachableFunction().