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[PGO] Don't unconditionally request BBInfo in verifyFuncBFI() #140804

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Merged
merged 4 commits into from
May 27, 2025
Merged

[PGO] Don't unconditionally request BBInfo in verifyFuncBFI() #140804

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cba5872
[CFGMST] Remove special case for entry block with no successors
aeubanks May 20, 2025
478d1eb
add CHECK
aeubanks May 20, 2025
5fda3c3
Update
aeubanks May 21, 2025
1a34e20
reuse BBInfo
aeubanks May 21, 2025
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8 changes: 5 additions & 3 deletions llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2086,10 +2086,12 @@ static void verifyFuncBFI(PGOUseFunc &Func, LoopInfo &LI,

unsigned BBNum = 0, BBMisMatchNum = 0, NonZeroBBNum = 0;
for (auto &BBI : F) {
uint64_t CountValue = 0;
uint64_t BFICountValue = 0;
PGOUseBBInfo *BBInfo = Func.findBBInfo(&BBI);
if (!BBInfo)
continue;
Comment on lines +2090 to +2091
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Should we emit a warning in this case? Why is it ok to silently ignore here?

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In an FDO-optimized build, hash mismatch errors are detected and logged (

llvm-project/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp

Lines 1431 to 1438 in 744a469

std::string Msg =
IPE.message() + std::string(" ") + F.getName().str() +
std::string(" Hash = ") + std::to_string(FuncInfo.FunctionHash) +
std::string(" up to ") + std::to_string(MismatchedFuncSum) +
std::string(" count discarded");
Ctx.diagnose(
DiagnosticInfoPGOProfile(M->getName().data(), Msg, DS_Warning));
).

Is it feasible to use similar mechanism to log the error here?

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only unreachable basic blocks don't have a BBInfo, those shouldn't matter

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In that case, is it possible to assert that BB is unreachable?

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I'm guessing DominatorTree wasn't (yet) computed in -O0 and he'd rather not compute it?


CountValue = Func.getBBInfo(&BBI).Count.value_or(CountValue);
uint64_t CountValue = Func.getBBInfo(&BBI).Count.value_or(CountValue);
uint64_t BFICountValue = 0;

BBNum++;
if (CountValue)
Expand Down
29 changes: 29 additions & 0 deletions llvm/test/Transforms/PGOProfile/unreachable_bb2.ll
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@@ -0,0 +1,29 @@
; RUN: split-file %s %t
; RUN: llvm-profdata merge %t/a.proftext -o %t/a.profdata
; RUN: opt < %t/a.ll -passes=pgo-instr-use -pgo-test-profile-file=%t/a.profdata -S | FileCheck %s

;--- a.ll

declare ptr @bar()

; CHECK: define ptr @foo
; Ensure the profile hash matches. If it doesn't we emit the "instr_prof_hash_mismatch" metadata.
; CHECK-NOT: instr_prof_hash_mismatch
define ptr @foo() {
entry:
ret ptr null

2:
ret ptr null
}

;--- a.proftext
# IR level Instrumentation Flag
:ir
foo
# Func Hash:
742261418966908927
# Num Counters:
1
# Counter Values:
1