https://github.com/mtrofin updated
https://github.com/llvm/llvm-project/pull/145578
>From e2f673682594ceafc73e5b7765934caabffd4907 Mon Sep 17 00:00:00 2001
From: Mircea Trofin <mtro...@google.com>
Date: Tue, 24 Jun 2025 09:50:40 -0700
Subject: [PATCH] [pgo] add means to specify "unknown" MD_prof
---
llvm/include/llvm/IR/ProfDataUtils.h | 12 +++
llvm/lib/IR/ProfDataUtils.cpp | 22 +++++
llvm/lib/IR/Verifier.cpp | 46 +++++++---
llvm/test/Verifier/branch-weight.ll | 130 +++++++++++++++++++++++++--
4 files changed, 187 insertions(+), 23 deletions(-)
diff --git a/llvm/include/llvm/IR/ProfDataUtils.h
b/llvm/include/llvm/IR/ProfDataUtils.h
index 8e8d069b836f1..89fa7f735f5d4 100644
--- a/llvm/include/llvm/IR/ProfDataUtils.h
+++ b/llvm/include/llvm/IR/ProfDataUtils.h
@@ -133,6 +133,18 @@ LLVM_ABI bool extractProfTotalWeight(const Instruction &I,
LLVM_ABI void setBranchWeights(Instruction &I, ArrayRef<uint32_t> Weights,
bool IsExpected);
+/// Specify that the branch weights for this terminator cannot be known at
+/// compile time. This should only be called by passes, and never as a default
+/// behavior in e.g. MDBuilder. The goal is to use this info to validate passes
+/// do not accidentally drop profile info, and this API is called in cases
where
+/// the pass explicitly cannot provide that info. Defaulting it in would hide
+/// bugs where the pass forgets to transfer over or otherwise specify profile
+/// info.
+LLVM_ABI void setExplicitlyUnknownBranchWeights(Instruction &I);
+
+LLVM_ABI bool isExplicitlyUnknownBranchWeightsMetadata(const MDNode &MD);
+LLVM_ABI bool hasExplicitlyUnknownBranchWeights(const Instruction &I);
+
/// Scaling the profile data attached to 'I' using the ratio of S/T.
LLVM_ABI void scaleProfData(Instruction &I, uint64_t S, uint64_t T);
diff --git a/llvm/lib/IR/ProfDataUtils.cpp b/llvm/lib/IR/ProfDataUtils.cpp
index 21524eb840539..1585771c0d0ae 100644
--- a/llvm/lib/IR/ProfDataUtils.cpp
+++ b/llvm/lib/IR/ProfDataUtils.cpp
@@ -44,6 +44,8 @@ constexpr unsigned MinBWOps = 3;
// the minimum number of operands for MD_prof nodes with value profiles
constexpr unsigned MinVPOps = 5;
+const char *UnknownBranchWeightsMarker = "unknown";
+
// We may want to add support for other MD_prof types, so provide an
abstraction
// for checking the metadata type.
bool isTargetMD(const MDNode *ProfData, const char *Name, unsigned MinOps) {
@@ -232,6 +234,26 @@ bool extractProfTotalWeight(const Instruction &I, uint64_t
&TotalVal) {
return extractProfTotalWeight(I.getMetadata(LLVMContext::MD_prof), TotalVal);
}
+void setExplicitlyUnknownBranchWeights(Instruction &I) {
+ MDBuilder MDB(I.getContext());
+ I.setMetadata(LLVMContext::MD_prof,
+ MDNode::get(I.getContext(),
+ MDB.createString(UnknownBranchWeightsMarker)));
+}
+
+bool isExplicitlyUnknownBranchWeightsMetadata(const MDNode &MD) {
+ if (MD.getNumOperands() != 1)
+ return false;
+ return MD.getOperand(0).equalsStr(UnknownBranchWeightsMarker);
+}
+
+bool hasExplicitlyUnknownBranchWeights(const Instruction &I) {
+ auto *MD = I.getMetadata(LLVMContext::MD_prof);
+ if (!MD)
+ return false;
+ return isExplicitlyUnknownBranchWeightsMetadata(*MD);
+}
+
void setBranchWeights(Instruction &I, ArrayRef<uint32_t> Weights,
bool IsExpected) {
MDBuilder MDB(I.getContext());
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index ae95e3e2bff8d..98fc31f75a031 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -2508,6 +2508,12 @@ void Verifier::verifyFunctionMetadata(
for (const auto &Pair : MDs) {
if (Pair.first == LLVMContext::MD_prof) {
MDNode *MD = Pair.second;
+ if (isExplicitlyUnknownBranchWeightsMetadata(*MD)) {
+ CheckFailed("'unknown' !prof metadata should appear only on "
+ "instructions supporting the 'branch_weights' metadata",
+ MD);
+ continue;
+ }
Check(MD->getNumOperands() >= 2,
"!prof annotations should have no less than 2 operands", MD);
@@ -4964,6 +4970,30 @@ void Verifier::visitDereferenceableMetadata(Instruction&
I, MDNode* MD) {
}
void Verifier::visitProfMetadata(Instruction &I, MDNode *MD) {
+ auto GetBranchingTerminatorNumOperands = [&]() {
+ unsigned ExpectedNumOperands = 0;
+ if (BranchInst *BI = dyn_cast<BranchInst>(&I))
+ ExpectedNumOperands = BI->getNumSuccessors();
+ else if (SwitchInst *SI = dyn_cast<SwitchInst>(&I))
+ ExpectedNumOperands = SI->getNumSuccessors();
+ else if (isa<CallInst>(&I))
+ ExpectedNumOperands = 1;
+ else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(&I))
+ ExpectedNumOperands = IBI->getNumDestinations();
+ else if (isa<SelectInst>(&I))
+ ExpectedNumOperands = 2;
+ else if (CallBrInst *CI = dyn_cast<CallBrInst>(&I))
+ ExpectedNumOperands = CI->getNumSuccessors();
+ return ExpectedNumOperands;
+ };
+ if (isExplicitlyUnknownBranchWeightsMetadata(*MD)) {
+ Check(GetBranchingTerminatorNumOperands() != 0 || isa<InvokeInst>(I),
+ "'unknown' !prof should only appear on instructions on which "
+ "'branch_weigths' would",
+ MD);
+ return;
+ }
+
Check(MD->getNumOperands() >= 2,
"!prof annotations should have no less than 2 operands", MD);
@@ -4981,20 +5011,8 @@ void Verifier::visitProfMetadata(Instruction &I, MDNode
*MD) {
Check(NumBranchWeights == 1 || NumBranchWeights == 2,
"Wrong number of InvokeInst branch_weights operands", MD);
} else {
- unsigned ExpectedNumOperands = 0;
- if (BranchInst *BI = dyn_cast<BranchInst>(&I))
- ExpectedNumOperands = BI->getNumSuccessors();
- else if (SwitchInst *SI = dyn_cast<SwitchInst>(&I))
- ExpectedNumOperands = SI->getNumSuccessors();
- else if (isa<CallInst>(&I))
- ExpectedNumOperands = 1;
- else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(&I))
- ExpectedNumOperands = IBI->getNumDestinations();
- else if (isa<SelectInst>(&I))
- ExpectedNumOperands = 2;
- else if (CallBrInst *CI = dyn_cast<CallBrInst>(&I))
- ExpectedNumOperands = CI->getNumSuccessors();
- else
+ const unsigned ExpectedNumOperands = GetBranchingTerminatorNumOperands();
+ if (ExpectedNumOperands == 0)
CheckFailed("!prof branch_weights are not allowed for this
instruction",
MD);
diff --git a/llvm/test/Verifier/branch-weight.ll
b/llvm/test/Verifier/branch-weight.ll
index 18e64b01a3d42..5be33098f4938 100644
--- a/llvm/test/Verifier/branch-weight.ll
+++ b/llvm/test/Verifier/branch-weight.ll
@@ -1,21 +1,65 @@
; Test MD_prof validation
; RUN: split-file %s %t
+
; RUN: opt -passes=verify %t/valid.ll --disable-output
-; RUN: not opt -passes=verify %t/invalid1.ll --disable-output 2>&1 | FileCheck
%s
-; RUN: not opt -passes=verify %t/invalid2.ll --disable-output 2>&1 | FileCheck
%s
+
+; RUN: not opt -passes=verify %t/wrong-count.ll --disable-output 2>&1 |
FileCheck %s --check-prefix=WRONG-COUNT
+; RUN: not opt -passes=verify %t/invalid-name1.ll --disable-output 2>&1 |
FileCheck %s
+; RUN: not opt -passes=verify %t/invalid-name2.ll --disable-output 2>&1 |
FileCheck %s
+
+; RUN: opt -passes=verify %t/unknown-correct.ll --disable-output
+
+; RUN: not opt -passes=verify %t/unknown-invalid.ll --disable-output 2>&1 |
FileCheck %s
+; RUN: not opt -passes=verify %t/unknown-on-function1.ll --disable-output 2>&1
| FileCheck %s --check-prefix=ON-FUNCTION1
+; RUN: not opt -passes=verify %t/unknown-on-function2.ll --disable-output 2>&1
| FileCheck %s --check-prefix=ON-FUNCTION2
+; RUN: not opt -passes=verify %t/invalid-unknown-placement.ll --disable-output
2>&1 | FileCheck %s --check-prefix=INVALID-UNKNOWN-PLACEMENT
;--- valid.ll
-define void @test(i1 %0) {
- br i1 %0, label %2, label %3, !prof !0
-2:
+declare void @to_invoke()
+declare i32 @__gxx_personality_v0(...)
+
+define void @invoker() personality ptr @__gxx_personality_v0 {
+ invoke void @to_invoke() to label %exit unwind label %lpad, !prof !0
+lpad:
+ %ll = landingpad {ptr, i32}
+ cleanup
ret void
-3:
+exit:
ret void
}
+
+define i32 @test(i32 %a) {
+ %c = icmp eq i32 %a, 0
+ br i1 %c, label %yes, label %exit, !prof !0
+yes:
+ switch i32 %a, label %exit [ i32 1, label %case_b
+ i32 2, label %case_c], !prof !1
+case_b:
+ br label %exit
+case_c:
+ br label %exit
+exit:
+ %r = select i1 %c, i32 1, i32 2, !prof !0
+ ret i32 %r
+}
!0 = !{!"branch_weights", i32 1, i32 2}
+!1 = !{!"branch_weights", i32 1, i32 2, i32 3}
+
+;--- wrong-count.ll
+define void @test(i32 %a) {
+ %c = icmp eq i32 %a, 0
+ br i1 %c, label %yes, label %no, !prof !0
+yes:
+ ret void
+no:
+ ret void
+}
+!0 = !{!"branch_weights", i32 1, i32 2, i32 3}
-;--- invalid1.ll
+; WRONG-COUNT: Wrong number of operands
+
+;--- invalid-name1.ll
define void @test(i1 %0) {
br i1 %0, label %2, label %3, !prof !0
2:
@@ -25,7 +69,7 @@ define void @test(i1 %0) {
}
!0 = !{!"invalid", i32 1, i32 2}
-;--- invalid2.ll
+;--- invalid-name2.ll
define void @test(i1 %0) {
br i1 %0, label %2, label %3, !prof !0
2:
@@ -36,4 +80,72 @@ define void @test(i1 %0) {
!0 = !{!"function_entry_count", i32 1}
-; CHECK: expected either branch_weights or VP profile name
\ No newline at end of file
+; CHECK: expected either branch_weights or VP profile name
+
+;--- unknown-correct.ll
+declare void @to_invoke()
+declare i32 @__gxx_personality_v0(...)
+
+define void @invoker() personality ptr @__gxx_personality_v0 {
+ invoke void @to_invoke() to label %exit unwind label %lpad, !prof !0
+lpad:
+ %ll = landingpad {ptr, i32}
+ cleanup
+ ret void
+exit:
+ ret void
+}
+
+define i32 @test(i32 %a) {
+ %c = icmp eq i32 %a, 0
+ br i1 %c, label %yes, label %exit, !prof !0
+yes:
+ switch i32 %a, label %exit [ i32 1, label %case_b
+ i32 2, label %case_c], !prof !0
+case_b:
+ br label %exit
+case_c:
+ br label %exit
+exit:
+ %r = select i1 %c, i32 1, i32 2, !prof !0
+ ret i32 %r
+}
+
+!0 = !{!"unknown"}
+
+;--- unknown-invalid.ll
+define void @test(i32 %a) {
+ %c = icmp eq i32 %a, 0
+ br i1 %c, label %yes, label %no, !prof !0
+yes:
+ ret void
+no:
+ ret void
+}
+
+!0 = !{!"unknown", i32 12, i32 67}
+
+;--- unknown-on-function1.ll
+define void @test() !prof !0 {
+ ret void
+}
+
+!0 = !{!"unknown"}
+; ON-FUNCTION1: 'unknown' !prof metadata should appear only on instructions
supporting the 'branch_weights' metadata
+
+;--- unknown-on-function2.ll
+define void @test() !prof !0 {
+ ret void
+}
+
+!0 = !{!"unknown", i64 123}
+; ON-FUNCTION2: first operand should be 'function_entry_count' or
'synthetic_function_entry_count'
+
+;--- invalid-unknown-placement.ll
+define i32 @test() {
+ %r = add i32 1, 2, !prof !0
+ ret i32 %r
+}
+!0 = !{!"unknown"}
+
+; INVALID-UNKNOWN-PLACEMENT: 'unknown' !prof should only appear on
instructions on which 'branch_weigths' would
\ No newline at end of file
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