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Fix MergeBlock error: a merge block for another header #3280

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Fix MergeBlock error: a merge block for another header #3280

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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
ea9c2af
MergeBlock test
pvelesko Jul 23, 2025
5185e41
fix blockMerge
pvelesko Jul 23, 2025
1a3a3c9
move test file
pvelesko Jul 27, 2025
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10 changes: 7 additions & 3 deletions lib/SPIRV/SPIRVWriter.cpp
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Expand Up @@ -2453,7 +2453,11 @@ LLVMToSPIRVBase::transValueWithoutDecoration(Value *V, SPIRVBasicBlock *BB,
Function *Fun = Branch->getFunction();
DominatorTree DomTree(*Fun);
LoopInfo LI(DomTree);
for (const auto *LoopObj : LI.getLoopsInPreorder()) {
// Find the innermost loop that contains the current basic block
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Suggested change
// Find the innermost loop that contains the current basic block
// Find the innermost loop that contains the current basic block.

BasicBlock *CurrentBB = Branch->getParent();
const Loop *ContainingLoop = LI.getLoopFor(CurrentBB);

if (ContainingLoop) {
// Check whether SuccessorFalse or SuccessorTrue is the loop header BB.
// For example consider following LLVM IR:
// br i1 %compare, label %for.body, label %for.end
Expand All @@ -2462,12 +2466,12 @@ LLVMToSPIRVBase::transValueWithoutDecoration(Value *V, SPIRVBasicBlock *BB,
// <- SuccessorTrue is 'for.end' aka successor(1)
// meanwhile the true successor (by definition) should be a loop header
// aka 'for.body'
if (LoopObj->getHeader() == Branch->getSuccessor(1))
if (ContainingLoop->getHeader() == Branch->getSuccessor(1))
// SuccessorFalse is the loop header BB.
BM->addLoopMergeInst(SuccessorTrue->getId(), // Merge Block
BB->getId(), // Continue Target
LoopControl, Parameters, SuccessorFalse);
else
else if (ContainingLoop->getHeader() == Branch->getSuccessor(0))
// SuccessorTrue is the loop header BB.
BM->addLoopMergeInst(SuccessorFalse->getId(), // Merge Block
BB->getId(), // Continue Target
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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)
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
return addInstruction(
new SPIRVLoopMerge(MergeBlock, ContinueTarget, LoopControl,
LoopControlParameters, BB),
BB);
}
}

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)
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
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
; 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: BranchConditional
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Please, add newline at end of file.

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should we add NEXT to verify that LoopMerge is immediately preceding?

Suggested change
; CHECK-SPIRV-TEXT: BranchConditional
; CHECK-SPIRV-TEXT-NEXT: BranchConditional

10 changes: 10 additions & 0 deletions test/OpLoopMerge_mergeBlock.ll
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@@ -0,0 +1,10 @@
; Test case for OpLoopMerge merge block assignment validation.
; This test verifies that OpLoopMerge instructions properly assign unique merge blocks
; and don't create conflicts where the same block is used as a merge block for multiple loops.

; RUN: llvm-spirv %S/mergeBlock.bc -o %t.spv
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Please, add the test contents in plain text in this file and call llvm-as from here.

; 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: BranchConditional
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Please, add newline at end of file.

Binary file added test/loopMerge.bc
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@YixingZhang007 YixingZhang007 Oct 16, 2025 •
edited
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I think these binary file should be removed from the PR.

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and the same for the other .bc file.

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Binary file added test/mergeBlock.bc
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