[PGO] Do not create block count annotations when all weights are 0,

avoiding an assertion.

A BB with a nonzero count, whose successor blocks all have 0 counts, could
cause an assertion. Don't create any branch weights in this case.

Reviewed By: xur

Differential Revision: https://reviews.llvm.org/D134203
This commit is contained in:
Wolfgang Pieb 2022-09-16 09:40:14 -07:00
parent 1532be98f9
commit b43a1d1bd9
4 changed files with 75 additions and 2 deletions

View File

@ -1689,7 +1689,21 @@ void PGOUseFunc::setBranchWeights() {
MaxCount = EdgeCount;
EdgeCounts[SuccNum] = EdgeCount;
}
if (MaxCount)
setProfMetadata(M, TI, EdgeCounts, MaxCount);
else {
// A zero MaxCount can come about when we have a BB with a positive
// count, and whose successor blocks all have 0 count. This can happen
// when there is no exit block and the code exits via a noreturn function.
auto &Ctx = M->getContext();
Ctx.diagnose(DiagnosticInfoPGOProfile(
M->getName().data(),
Twine("Profile in ") + F.getName().str() +
Twine(" partially ignored") +
Twine(", possibly due to the lack of a return path."),
DS_Warning));
}
}
}

View File

@ -440,6 +440,7 @@ bool MemOPSizeOpt::perform(MemOp MO) {
DTU.applyUpdates(Updates);
Updates.clear();
if (MaxCount)
setProfMetadata(Func.getParent(), SI, CaseCounts, MaxCount);
LLVM_DEBUG(dbgs() << *BB << "\n");

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@ -0,0 +1,11 @@
# IR level Instrumentation Flag
:ir
foo
# Func Hash:
146835645050580305
# Num Counters:
3
# Counter Values:
0
1
0

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@ -0,0 +1,47 @@
; Make sure a profile that is generated from a function without an exit node
; does not cause an assertion. The profile consists of a non-zero count in a
; basic block and 0 counts in all succcessor blocks. Expect a warning.
; RUN: llvm-profdata merge %S/Inputs/maxcountzero.proftext -o %t.profdata
; RUN: opt < %s -passes=pgo-instr-use -pgo-instrument-entry=false -pgo-test-profile-file=%t.profdata -S 2>&1 | FileCheck %s
define void @bar(i32 noundef %s) {
entry:
%cmp = icmp sgt i32 %s, 20
br i1 %cmp, label %if.then, label %if.end
if.then:
call void @exit(i32 noundef 1)
unreachable
if.end:
ret void
}
declare void @exit(i32 noundef)
define void @foo(i32 noundef %n) {
entry:
%sum = alloca i32, align 4
store volatile i32 %n, ptr %sum, align 4
%sum.0.sum.0. = load volatile i32, ptr %sum, align 4
call void @bar(i32 noundef %sum.0.sum.0.)
%cmp = icmp slt i32 %n, 10
br i1 %cmp, label %if.then, label %if.end
if.then:
%sum.0.sum.0.1 = load volatile i32, ptr %sum, align 4
call void @bar(i32 noundef %sum.0.sum.0.1)
br label %if.end
if.end:
br label %for.cond
for.cond:
%sum.0.sum.0.2 = load volatile i32, ptr %sum, align 4
call void @bar(i32 noundef %sum.0.sum.0.2)
br label %for.cond
}
; CHECK: warning:{{.*}}Profile in foo partially ignored
; CHECK: define