[llvm] [PGO] Skip optimizing probes that don't fit. (PR #70875)
Davide Italiano via llvm-commits
llvm-commits at lists.llvm.org
Tue Oct 31 17:22:37 PDT 2023
https://github.com/dcci updated https://github.com/llvm/llvm-project/pull/70875
>From dd743477a28ba770e11f67d5f000f6e87cdb2e7b Mon Sep 17 00:00:00 2001
From: Davide Italiano <davidino at fb.com>
Date: Tue, 31 Oct 2023 16:20:51 -0700
Subject: [PATCH] [PGO] Skip optimizing probes that don't fit.
The discriminator can only pack 16 bits, so anything exceeding
that value will cause the packing code to crash. Emit a diagnostic
and skip the optimization instead.
---
llvm/lib/Transforms/IPO/SampleProfileProbe.cpp | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/llvm/lib/Transforms/IPO/SampleProfileProbe.cpp b/llvm/lib/Transforms/IPO/SampleProfileProbe.cpp
index 56d711c588b0755..1d312981bd1860b 100644
--- a/llvm/lib/Transforms/IPO/SampleProfileProbe.cpp
+++ b/llvm/lib/Transforms/IPO/SampleProfileProbe.cpp
@@ -18,6 +18,7 @@
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DebugInfoMetadata.h"
+#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/IntrinsicInst.h"
@@ -221,12 +222,26 @@ void SampleProfileProber::computeProbeIdForBlocks() {
}
void SampleProfileProber::computeProbeIdForCallsites() {
+ LLVMContext &Ctx = F->getContext();
+ Module *M = F->getParent();
+
for (auto &BB : *F) {
for (auto &I : BB) {
if (!isa<CallBase>(I))
continue;
if (isa<IntrinsicInst>(&I))
continue;
+
+ // There's a limit on the number of probe indices that can be optimized.
+ // The current implementation uses the lower 16 bits of the discriminator
+ // so anything larger than 0xFFFF will be ignored.
+ if (LastProbeId >= 0xFFFF) {
+ std::string Msg = "Pseudo instrumentation incomplete for " +
+ std::string(F->getName()) + " because it's too large";
+ Ctx.diagnose(DiagnosticInfoSampleProfile(M->getName().data(), Msg));
+ return;
+ }
+
CallProbeIds[&I] = ++LastProbeId;
}
}
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