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Fix LoopMerge Instruction Placement #3277

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Fix LoopMerge Instruction Placement #3277

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6fe270b
add LoopMerge test
pvelesko Jul 23, 2025
6544a09
Fix LoopMerge error
pvelesko Jul 23, 2025
606f935
move test files
pvelesko Jul 23, 2025
be04ac1
Update test/OpLoopMerge_loopMerge.ll
pvelesko Sep 30, 2025
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36 changes: 29 additions & 7 deletions lib/SPIRV/libSPIRV/SPIRVModule.cpp
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Expand Up @@ -1855,20 +1855,42 @@ SPIRVInstruction *SPIRVModuleImpl::addSelectionMergeInst(
SPIRVInstruction *SPIRVModuleImpl::addLoopMergeInst(
SPIRVId MergeBlock, SPIRVId ContinueTarget, SPIRVWord LoopControl,
std::vector<SPIRVWord> LoopControlParameters, SPIRVBasicBlock *BB) {
return addInstruction(
new SPIRVLoopMerge(MergeBlock, ContinueTarget, LoopControl,
LoopControlParameters, BB),
BB, const_cast<SPIRVInstruction *>(BB->getTerminateInstr()));
SPIRVInstruction *TermInst = const_cast<SPIRVInstruction *>(BB->getTerminateInstr());
// OpLoopMerge must be the second-to-last instruction in the block,
// immediately preceding the branch instruction (OpBranch or OpBranchConditional)
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Suggested change
// immediately preceding the branch instruction (OpBranch or OpBranchConditional)
// immediately preceding the branch instruction (OpBranch or OpBranchConditional).

if (TermInst && (TermInst->getOpCode() == OpBranch ||
TermInst->getOpCode() == OpBranchConditional)) {
return addInstruction(
new SPIRVLoopMerge(MergeBlock, ContinueTarget, LoopControl,
LoopControlParameters, BB),
BB, TermInst);
} else {
// If there's no proper terminator, add at the end
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Suggested change
// If there's no proper terminator, add at the end
// If there's no proper terminator, add at the end.

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Also, is this correct? You mentioned that the spec requires this instruction to immediately precede either an OpBranch or an OpBranchConditional. My understanding is that, if none of these exist, this instruction could not be placed. Maybe we should assert here instead?

return addInstruction(
new SPIRVLoopMerge(MergeBlock, ContinueTarget, LoopControl,
LoopControlParameters, BB),
BB);
}
Comment on lines +1867 to +1873
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Probably clang-tidy will recommend to remove else as previous if terminates with return.

}

SPIRVInstruction *SPIRVModuleImpl::addLoopControlINTELInst(
SPIRVWord LoopControl, std::vector<SPIRVWord> LoopControlParameters,
SPIRVBasicBlock *BB) {
addCapability(CapabilityUnstructuredLoopControlsINTEL);
addExtension(ExtensionID::SPV_INTEL_unstructured_loop_controls);
return addInstruction(
new SPIRVLoopControlINTEL(LoopControl, LoopControlParameters, BB), BB,
const_cast<SPIRVInstruction *>(BB->getTerminateInstr()));
SPIRVInstruction *TermInst = const_cast<SPIRVInstruction *>(BB->getTerminateInstr());
// OpLoopControlINTEL must be the second-to-last instruction in the block,
// immediately preceding the branch instruction (OpBranch or OpBranchConditional)
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Suggested change
// immediately preceding the branch instruction (OpBranch or OpBranchConditional)
// immediately preceding the branch instruction (OpBranch or OpBranchConditional).

if (TermInst && (TermInst->getOpCode() == OpBranch ||
TermInst->getOpCode() == OpBranchConditional)) {
return addInstruction(
new SPIRVLoopControlINTEL(LoopControl, LoopControlParameters, BB), BB,
TermInst);
} else {
// If there's no proper terminator, add at the end
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Suggested change
// If there's no proper terminator, add at the end
// If there's no proper terminator, add at the end.

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Same than earlier. Is this compliant with the spec? Should we assert/report error instead?

return addInstruction(
new SPIRVLoopControlINTEL(LoopControl, LoopControlParameters, BB), BB);
}
}

SPIRVInstruction *SPIRVModuleImpl::addFixedPointIntelInst(
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10 changes: 10 additions & 0 deletions test/OpLoopMerge_loopMerge.ll
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@@ -0,0 +1,10 @@
; Test case for OpLoopMerge instruction placement validation.
; This test verifies that OpLoopMerge instructions are properly placed as the second-to-last
; instruction in their basic block, immediately preceding the branch instruction.

; RUN: llvm-spirv %S/loopMerge.bc -o %t.spv
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Please move .bc file content to the text and call llvm-as in the test before the translation.

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+1.

; RUN: spirv-val %t.spv

; RUN: llvm-spirv --to-text %t.spv -o - | FileCheck %s --check-prefix=CHECK-SPIRV-TEXT
; CHECK-SPIRV-TEXT: LoopMerge
; CHECK-SPIRV-TEXT-NEXT: BranchConditional
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Please, add newline at end of file.

Binary file added test/loopMerge.bc
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