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[WPD][ThinLTO]Add cutoff option for WPD #113383

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Oct 24, 2024
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[WPD][ThinLTO]Add cutoff option for WPD #113383

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29a4c14
[WPD][ThinLTO]Add cutoff option for WPD
mingmingl-llvm Oct 22, 2024
5c7902d
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mingmingl-llvm Oct 24, 2024
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17 changes: 17 additions & 0 deletions llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -168,6 +168,14 @@ static cl::list<std::string>
cl::desc("Prevent function(s) from being devirtualized"),
cl::Hidden, cl::CommaSeparated);

/// 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 @@ -316,6 +324,9 @@ 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 @@ -1169,10 +1180,16 @@ void DevirtModule::applySingleImplDevirt(VTableSlotInfo &SlotInfo,
if (!OptimizedCalls.insert(&VCallSite.CB).second)
continue;

// Stop when the number of devirted calls reaches the cutoff.
if (WholeProgramDevirtCutoff.getNumOccurrences() > 0 &&
NumDevirtCalls >= WholeProgramDevirtCutoff)
return;

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
6 changes: 6 additions & 0 deletions llvm/test/Transforms/WholeProgramDevirt/import.ll
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Expand Up @@ -8,6 +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.
; 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
target datalayout = "e-p:64:64"
target triple = "x86_64-unknown-linux-gnu"

Expand Down
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