[OMPIRBuilder][debug] Dont drop debug info for loop constructs.

In OMPIRBuilder, we have many cases where we dont handle the debug
location correctly while chaning the location or insertion point. This
is one of those cases.

Please see the following test program.
program main
  implicit none
  integer i, j
  integer array(16384)

!$omp target teams distribute
  DO i=1,16384
    !$omp parallel do
      DO j=1,16384
        array(j) = i
      ENDDO
    !$omp end parallel do
  ENDDO
!$omp end target teams distribute

print *, array
end program main

When tried to compile with the follownig command
flang -g -O2 -fopenmp  test.f90 -o test  --offload-arch=gfx90a

will fail in the verification with the following errors:
!dbg attachment points at wrong subprogram for function

This happens because we were dropping the debug locatoin in the
createCanonicalLoop so the call to the functions like
__kmpc_distribute_static_4u was without a debug locations. When it gets
inlined, the locations inside it are not adjusted as the call
instruction does not have the debug locations
(llvm/lib/Transforms/Utils/InlineFunction.cpp:fixupLineNumbers).

Later Verifier finds that this call have instruction with debug locations
that point to another function and fails. The fix is simple to not drop
the debug location.

Author: abidh

llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp

@@ -4184,7 +4184,11 @@ Expected<CanonicalLoopInfo *> OpenMPIRBuilder::createCanonicalLoop(
     Value *IndVar = Builder.CreateAdd(Span, Start);
     return BodyGenCB(Builder.saveIP(), IndVar);
   };
-  LocationDescription LoopLoc = ComputeIP.isSet() ? Loc.IP : Builder.saveIP();
+  LocationDescription LoopLoc =
+      ComputeIP.isSet()
+          ? Loc
+          : LocationDescription(Builder.saveIP(),
+                                Builder.getCurrentDebugLocation());
   return createCanonicalLoop(LoopLoc, BodyGen, TripCount, Name);
 }
 

mlir/test/Target/LLVMIR/omptarget-debug-loop-loc.mlir

@@ -0,0 +1,66 @@
+// RUN: mlir-translate -mlir-to-llvmir %s | FileCheck %s
+
+module attributes {dlti.dl_spec = #dlti.dl_spec<#dlti.dl_entry<"dlti.alloca_memory_space", 5 : ui32>>, llvm.target_triple = "amdgcn-amd-amdhsa", omp.is_target_device = true} {
+  omp.private {type = private} @_QFEj_private_i32 : i32 loc(#loc1)
+  omp.private {type = private} @_QFEi_private_i32 : i32 loc(#loc1)
+  llvm.func @test() {
+    %3 = llvm.mlir.constant(1 : i64) : i64
+    %4 = llvm.alloca %3 x i32 {bindc_name = "j"} : (i64) -> !llvm.ptr<5> loc(#loc4)
+    %5 = llvm.addrspacecast %4 : !llvm.ptr<5> to !llvm.ptr loc(#loc4)
+    %6 = llvm.mlir.constant(1 : i64) : i64
+    %7 = llvm.alloca %6 x i32 {bindc_name = "i"} : (i64) -> !llvm.ptr<5> loc(#loc4)
+    %8 = llvm.addrspacecast %7 : !llvm.ptr<5> to !llvm.ptr
+    %9 = llvm.mlir.constant(16383 : index) : i64
+    %10 = llvm.mlir.constant(0 : index) : i64
+    %11 = llvm.mlir.constant(1 : index) : i64
+    %12 = llvm.mlir.constant(16384 : i32) : i32
+    %14 = llvm.mlir.addressof @_QFEarray : !llvm.ptr
+    %18 = omp.map.info var_ptr(%8 : !llvm.ptr, i32) map_clauses(implicit, exit_release_or_enter_alloc) capture(ByCopy) -> !llvm.ptr {name = "i"} loc(#loc3)
+    %20 = omp.map.info var_ptr(%5 : !llvm.ptr, i32) map_clauses(implicit, exit_release_or_enter_alloc) capture(ByCopy) -> !llvm.ptr {name = "j"} loc(#loc3)
+    %22 = omp.map.bounds lower_bound(%10 : i64) upper_bound(%9 : i64) extent(%9 : i64) stride(%11 : i64) start_idx(%11 : i64) loc(#loc3)
+    %23 = omp.map.info var_ptr(%14 : !llvm.ptr, !llvm.array<16384 x i32>) map_clauses(implicit, tofrom) capture(ByRef) bounds(%22) -> !llvm.ptr {name = "array"} loc(#loc3)
+    %24 = omp.map.info var_ptr(%8 : !llvm.ptr, i32) map_clauses(implicit, exit_release_or_enter_alloc) capture(ByCopy) -> !llvm.ptr {name = "i"} loc(#loc3)
+    omp.target map_entries(%18 -> %arg0, %20 -> %arg2, %23 -> %arg4, %24 -> %arg5 : !llvm.ptr, !llvm.ptr, !llvm.ptr, !llvm.ptr) {
+      %25 = llvm.mlir.constant(1 : i32) : i32
+      %27 = llvm.mlir.constant(16384 : i32) : i32
+      omp.teams {
+        omp.distribute private(@_QFEi_private_i32 %arg5 -> %arg6 : !llvm.ptr) {
+          omp.loop_nest (%arg7) : i32 = (%25) to (%27) inclusive step (%25) {
+            omp.parallel {
+              omp.wsloop private(@_QFEj_private_i32 %arg2 -> %arg8 : !llvm.ptr) {
+                omp.loop_nest (%arg9) : i32 = (%25) to (%27) inclusive step (%25) {
+                  llvm.store %arg9, %arg8 : i32, !llvm.ptr loc(#loc9)
+                  omp.yield
+                } loc(#loc9)
+              } loc(#loc9)
+              omp.terminator loc(#loc9)
+            } loc(#loc9)
+            omp.yield loc(#loc9)
+          } loc(#loc9)
+        } loc(#loc9)
+        omp.terminator loc(#loc9)
+      } loc(#loc9)
+      omp.terminator loc(#loc9)
+    } loc(#loc9)
+    llvm.return loc(#loc9)
+  } loc(#loc14)
+  llvm.mlir.global internal @_QFEarray() {addr_space = 0 : i32} : !llvm.array<16384 x i32> {
+    %0 = llvm.mlir.zero : !llvm.array<16384 x i32>
+    llvm.return %0 : !llvm.array<16384 x i32>
+  } loc(#loc2)
+}
+#di_file = #llvm.di_file<"test.f90" in "">
+#di_null_type = #llvm.di_null_type
+#loc1 = loc("test.f90":4:23)
+#loc2 = loc("test.f90":4:15)
+#loc3 = loc("test.f90":1:7)
+#loc4 = loc("test.f90":4:18)
+#loc9 = loc("test.f90":13:11)
+#di_compile_unit = #llvm.di_compile_unit<id = distinct[0]<>, sourceLanguage = DW_LANG_Fortran95, file = #di_file, producer = "flang", isOptimized = true, emissionKind = LineTablesOnly>
+#di_subroutine_type = #llvm.di_subroutine_type<callingConvention = DW_CC_program, types = #di_null_type>
+#di_subprogram = #llvm.di_subprogram<id = distinct[1]<>, compileUnit = #di_compile_unit, scope = #di_file, name = "main", file = #di_file, subprogramFlags = "Definition|Optimized|MainSubprogram", type = #di_subroutine_type>
+#loc14 = loc(fused<#di_subprogram>[#loc3])
+
+
+// CHECK: call void @__kmpc_distribute_static{{.*}}!dbg
+