Retain llvm.loop metadata for LoopControlINTEL instruction

In case when debug information presents in the module, the
metadata was missing with translation back of LoopControlINTEL
instruction due to incorrect instruction ID.

Signed-off-by: Dmitry Sidorov <dmitry.sidorov@intel.com>

Author: MrSidims

llvm-spirv/lib/SPIRV/libSPIRV/SPIRVBasicBlock.cpp

@@ -70,7 +70,8 @@ SPIRVBasicBlock::addInstruction(SPIRVInstruction *I,
     // If insertion of a new instruction before the one passed to the function
     // is illegal, insertion before the returned instruction is guaranteed
     // to retain correct instruction order in a block
-    if (Pos != InstVec.begin() && isa<OpLoopMerge>(*std::prev(Pos)))
+    if (Pos != InstVec.begin() && (isa<OpLoopMerge>(*std::prev(Pos)) ||
+                                   isa<OpLoopControlINTEL>(*std::prev(Pos))))
       --Pos;
     InstVec.insert(Pos, I);
   } else

llvm-spirv/test/DebugInfo/DebugUnstructuredControlFlow.cl

@@ -0,0 +1,25 @@
+// RUN: %clang_cc1 -triple spir64-unknown-unknown -cl-std=CL2.0 -O0 -debug-info-kind=standalone -emit-llvm-bc %s -o %t.bc
+// RUN: llvm-spirv %t.bc --spirv-ext=+SPV_INTEL_unstructured_loop_controls -o %t.spv
+// RUN: llvm-spirv %t.spv --to-text -o %t.spt
+// RUN: FileCheck < %t.spt %s --check-prefix=CHECK-SPIRV
+// RUN: llvm-spirv -r %t.spv -o %t.bc
+// RUN: llvm-dis < %t.bc | FileCheck %s --check-prefix=CHECK-LLVM
+
+// Test that no debug info instruction is inserted between LoopControlINTEL and
+// Branch instructions. Otherwise, debug info interferes with SPIRVToLLVM
+// translation of structured flow control. Yet, Line DebugInfo instruction is
+// still presenting between LoopControlINTEL and Branch instructions.
+
+kernel
+void sample() {
+  #pragma clang loop unroll(full)
+  for(;;);
+}
+
+// CHECK-SPIRV: 2 LoopControlINTEL 1
+// CHECK-SPIRV-NOT: ExtInst
+// CHECK-SPIRV: {{[0-9]+}} Line {{[0-9]+}} {{[0-9]+}} {{[0-9]+}}
+// CHECK-SPIRV: Branch
+// CHECK-LLVM: br label %{{.*}}, !dbg !{{[0-9]+}}, !llvm.loop ![[MD:[0-9]+]]
+// CHECK-LLVM: ![[MD]] = distinct !{![[MD]], ![[MD_unroll:[0-9]+]]}
+// CHECK-LLVM: ![[MD_unroll]] = !{!"llvm.loop.unroll.enable"}