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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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2d70018
Add test for OpLoopMerge merge block conflict
pvelesko Dec 15, 2025
1bc6a52
Fix merge block conflict for nested loops
pvelesko Dec 15, 2025
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10 changes: 7 additions & 3 deletions lib/SPIRV/SPIRVWriter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2512,7 +2512,11 @@ 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.
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 @@ -2521,12 +2525,12 @@ 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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32 changes: 32 additions & 0 deletions test/OpLoopMerge_mergeBlock.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,32 @@
; RUN: llvm-as %s -o %t.bc
; RUN: llvm-spirv %t.bc -o %t.spv
; RUN: spirv-val %t.spv
; RUN: llvm-spirv --to-text %t.spv -o - | FileCheck %s

; CHECK: LoopMerge
; CHECK-NEXT: BranchConditional

target triple = "spir64"

define spir_kernel void @test(i32 %n) {
entry:
%cmp0 = icmp sgt i32 %n, 0
br i1 %cmp0, label %outer, label %exit
outer:
%i = phi i32 [ 0, %entry ], [ %i.next, %latch ]
%cmp1 = icmp eq i32 %i, 0
br i1 %cmp1, label %latch, label %inner
inner:
%cmp2 = icmp eq i32 %i, 1
br i1 %cmp2, label %latch, label %inner, !llvm.loop !1
latch:
%i.next = add i32 %i, 1
%cmp3 = icmp slt i32 %i.next, %n
br i1 %cmp3, label %outer, label %exit, !llvm.loop !0
exit:
ret void
}

!0 = distinct !{!0, !2}
!1 = distinct !{!1, !2}
!2 = !{!"llvm.loop.unroll.disable"}
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