From ae56ee948ce8cea60811b55ac129d297acf11885 Mon Sep 17 00:00:00 2001
From: Paulius Velesko <pvelesko@pglc.io>
Date: Mon, 15 Dec 2025 05:42:26 +0200
Subject: [PATCH 1/2] Add test for OpLoopMerge merge block conflict

---
 test/OpLoopMerge_mergeBlock.ll | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 test/OpLoopMerge_mergeBlock.ll

diff --git a/test/OpLoopMerge_mergeBlock.ll b/test/OpLoopMerge_mergeBlock.ll
new file mode 100644
index 0000000000..01ac1896d0
--- /dev/null
+++ b/test/OpLoopMerge_mergeBlock.ll
@@ -0,0 +1,28 @@
+; RUN: llvm-as %s -o %t.bc
+; RUN: llvm-spirv %t.bc -o %t.spv
+; RUN: spirv-val %t.spv
+
+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"}

From dbe6a98e7a8f05314bb1492a5b4044d49f187811 Mon Sep 17 00:00:00 2001
From: Paulius Velesko <pvelesko@pglc.io>
Date: Mon, 15 Dec 2025 05:42:53 +0200
Subject: [PATCH 2/2] Fix merge block conflict for nested loops

---
 lib/SPIRV/SPIRVWriter.cpp      | 10 +++++++---
 test/OpLoopMerge_mergeBlock.ll |  4 ++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/lib/SPIRV/SPIRVWriter.cpp b/lib/SPIRV/SPIRVWriter.cpp
index b6781226c2..0b468c2176 100644
--- a/lib/SPIRV/SPIRVWriter.cpp
+++ b/lib/SPIRV/SPIRVWriter.cpp
@@ -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
@@ -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
diff --git a/test/OpLoopMerge_mergeBlock.ll b/test/OpLoopMerge_mergeBlock.ll
index 01ac1896d0..883033eb8f 100644
--- a/test/OpLoopMerge_mergeBlock.ll
+++ b/test/OpLoopMerge_mergeBlock.ll
@@ -1,6 +1,10 @@
 ; 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"