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[WPD] Change Devirt Cutoff to use DebugCounter #170009

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[WPD] Change Devirt Cutoff to use DebugCounter #170009

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20 changes: 5 additions & 15 deletions llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -99,6 +99,7 @@
#include "llvm/IR/ProfDataUtils.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/DebugCounter.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/FileSystem.h"
Expand Down Expand Up @@ -130,6 +131,8 @@ 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.");

namespace llvm {

Expand Down Expand Up @@ -219,14 +222,6 @@ static cl::opt<bool> WholeProgramDevirtKeepUnreachableFunction(
cl::desc("Regard unreachable functions as possible devirtualize targets."),
cl::Hidden, cl::init(true));

/// If explicitly specified, the devirt module pass will stop transformation
/// once the total number of devirtualizations reach the cutoff value. Setting
/// this option to 0 explicitly will do 0 devirtualization.
static cl::opt<unsigned> WholeProgramDevirtCutoff(
"wholeprogramdevirt-cutoff",
cl::desc("Max number of devirtualizations for devirt module pass"),
cl::init(0));

/// 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
Expand Down Expand Up @@ -377,9 +372,6 @@ VirtualCallTarget::VirtualCallTarget(GlobalValue *Fn, const TypeMemberInfo *TM)

namespace {

// Tracks the number of devirted calls in the IR transformation.
static unsigned NumDevirtCalls = 0;

// A slot in a set of virtual tables. The TypeID identifies the set of virtual
// tables, and the ByteOffset is the offset in bytes from the address point to
// the virtual function pointer.
Expand Down Expand Up @@ -1216,15 +1208,13 @@ void DevirtModule::applySingleImplDevirt(VTableSlotInfo &SlotInfo,
continue;

// Stop when the number of devirted calls reaches the cutoff.
if (WholeProgramDevirtCutoff.getNumOccurrences() > 0 &&
NumDevirtCalls >= WholeProgramDevirtCutoff)
return;
if (!DebugCounter::shouldExecute(CallsToDevirt))
continue;

if (RemarksEnabled)
VCallSite.emitRemark("single-impl",
TheFn->stripPointerCasts()->getName(), OREGetter);
NumSingleImpl++;
NumDevirtCalls++;
auto &CB = VCallSite.CB;
assert(!CB.getCalledFunction() && "devirtualizing direct call?");
IRBuilder<> Builder(&CB);
Expand Down
10 changes: 5 additions & 5 deletions llvm/test/Transforms/WholeProgramDevirt/import.ll
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@mingmingl-llvm mingmingl-llvm Nov 29, 2025

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My understanding of

llvm-project/llvm/include/llvm/Support/DebugCounter.h

Lines 156 to 163 in 24b87b8

static bool isCountingEnabled() {
// Compile to nothing when debugging is off
#ifdef NDEBUG
return false;
#else
return instance().Enabled || instance().ShouldPrintCounter;
#endif
}

is that debug counter needs -DLLVM_ENABLE_ASSERTIONS=ON, and the test will need something like 'REQUIRES: asserts'.

Original file line number Diff line number Diff line change
Expand Up @@ -8,12 +8,12 @@
; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -wholeprogramdevirt-read-summary=%S/Inputs/import-vcp-branch-funnel.yaml < %s | FileCheck --check-prefixes=CHECK,VCP,VCP-X86,VCP64,BRANCH-FUNNEL %s
; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -wholeprogramdevirt-read-summary=%S/Inputs/import-branch-funnel.yaml < %s | FileCheck --check-prefixes=CHECK,BRANCH-FUNNEL,BRANCH-FUNNEL-NOVCP %s

; Cutoff value is not explicitly set. Expect 3 remark messages.
; Devirt calls debug counter is not explicitly set. Expect 3 remark messages.
; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -pass-remarks=wholeprogramdevirt -wholeprogramdevirt-read-summary=%S/Inputs/import-single-impl.yaml < %s 2>&1 | grep "single-impl" | count 3
; Cutoff value is set to 1. Expect one remark messages.
; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -pass-remarks=wholeprogramdevirt -wholeprogramdevirt-cutoff=1 -wholeprogramdevirt-read-summary=%S/Inputs/import-single-impl.yaml < %s 2>&1 | grep "single-impl" | count 1
; Cutoff value is explicitly set to zero. Expect no remark message.
; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -pass-remarks=wholeprogramdevirt -wholeprogramdevirt-cutoff=0 -wholeprogramdevirt-read-summary=%S/Inputs/import-single-impl.yaml < %s 2>&1 | FileCheck -implicit-check-not="remark" %s
; Devirt calls debug counter is set to 1. Expect one remark messages.
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@mingmingl-llvm mingmingl-llvm Nov 29, 2025

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nit: setting -debug-counter=calls-to-devirt=2 -print-debug-counter-queries devirts the third callsite, and grep "single-impl" also gives 1.

Could you tighten up the test to add -print-debug-counter-queries and also test that the debug counter output?

-debug-counter=calls-to-devirt=0 -print-debug-counter-queries gives the following output.

DebugCounter calls-to-devirt=0 execute
remark: <unknown>:0:0: single-impl: devirtualized a call to singleimpl1
DebugCounter calls-to-devirt=1 skip
DebugCounter calls-to-devirt=2 skip

; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -pass-remarks=wholeprogramdevirt -debug-counter=calls-to-devirt=0 -wholeprogramdevirt-read-summary=%S/Inputs/import-single-impl.yaml < %s 2>&1 | grep "single-impl" | count 1
; Devirt calls debug counter is set outside the range of calls. Expect no remark message.
; RUN: opt -S -passes=wholeprogramdevirt -wholeprogramdevirt-summary-action=import -pass-remarks=wholeprogramdevirt -debug-counter=calls-to-devirt=9999 -wholeprogramdevirt-read-summary=%S/Inputs/import-single-impl.yaml < %s 2>&1 | FileCheck -implicit-check-not="remark" %s
target datalayout = "e-p:64:64"
target triple = "x86_64-unknown-linux-gnu"

Expand Down