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[mlir][llvm] Fix import of branch weights with "expected" field #169776

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Merged
merged 1 commit into from
Nov 27, 2025
Merged

[mlir][llvm] Fix import of branch weights with "expected" field #169776

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23 changes: 18 additions & 5 deletions mlir/lib/Target/LLVMIR/Dialect/LLVMIR/LLVMIRToLLVMTranslation.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -113,7 +113,7 @@ static LogicalResult setProfilingAttr(OpBuilder &builder, llvm::MDNode *node,
return failure();

// Handle function entry count metadata.
if (name->getString() == "function_entry_count") {
if (name->getString() == llvm::MDProfLabels::FunctionEntryCount) {

// TODO support function entry count metadata with GUID fields.
if (node->getNumOperands() != 2)
Expand All @@ -131,15 +131,28 @@ static LogicalResult setProfilingAttr(OpBuilder &builder, llvm::MDNode *node,
<< "expected function_entry_count to be attached to a function";
}

if (name->getString() != "branch_weights")
if (name->getString() != llvm::MDProfLabels::BranchWeights)
return failure();
// The branch_weights metadata must have at least 2 operands.
if (node->getNumOperands() < 2)
return failure();

ArrayRef<llvm::MDOperand> branchWeightOperands =
node->operands().drop_front();
if (auto *mdString = dyn_cast<llvm::MDString>(node->getOperand(1))) {
if (mdString->getString() != llvm::MDProfLabels::ExpectedBranchWeights)
return failure();
// The MLIR WeightedBranchOpInterface does not support the
// ExpectedBranchWeights field, so it is dropped.
branchWeightOperands = branchWeightOperands.drop_front();
}

// Handle branch weights metadata.
SmallVector<int32_t> branchWeights;
branchWeights.reserve(node->getNumOperands() - 1);
for (unsigned i = 1, e = node->getNumOperands(); i != e; ++i) {
branchWeights.reserve(branchWeightOperands.size());
for (const llvm::MDOperand &operand : branchWeightOperands) {
llvm::ConstantInt *branchWeight =
llvm::mdconst::dyn_extract<llvm::ConstantInt>(node->getOperand(i));
llvm::mdconst::dyn_extract<llvm::ConstantInt>(operand);
if (!branchWeight)
return failure();
branchWeights.push_back(branchWeight->getZExtValue());
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36 changes: 36 additions & 0 deletions mlir/test/Target/LLVMIR/Import/metadata-profiling.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,22 @@ bb2:

; // -----

; CHECK-LABEL: @cond_br_expected
define i64 @cond_br_expected(i1 %arg1, i64 %arg2) {
entry:
; CHECK: llvm.cond_br
; CHECK-SAME: weights([1, 2000])
br i1 %arg1, label %bb1, label %bb2, !prof !0
bb1:
ret i64 %arg2
bb2:
ret i64 %arg2
}

!0 = !{!"branch_weights", !"expected", i32 1, i32 2000}

; // -----

; CHECK-LABEL: @simple_switch(
define i32 @simple_switch(i32 %arg1) {
; CHECK: llvm.switch
Expand All @@ -36,6 +52,26 @@ bbd:

; // -----

; CHECK-LABEL: @simple_switch_expected(
define i32 @simple_switch_expected(i32 %arg1) {
; CHECK: llvm.switch
; CHECK: {branch_weights = array<i32: 1, 1, 2000>}
switch i32 %arg1, label %bbd [
i32 0, label %bb1
i32 9, label %bb2
], !prof !0
bb1:
ret i32 %arg1
bb2:
ret i32 %arg1
bbd:
ret i32 %arg1
}

!0 = !{!"branch_weights", !"expected", i32 1, i32 1, i32 2000}

; // -----

; Verify that a single weight attached to a call is not translated.
; The MLIR WeightedBranchOpInterface does not support this case.

Expand Down