lattner
commented
13 years ago Dan, can you take a look at this?
Open llvmbot opened 13 years ago
lattner
commented
13 years ago Dan, can you take a look at this?
llvmbot
commented
13 years ago Yeah, that is true, but this is a -O0 compilation. If the user wants fast compilation they can use -O[1-3]. -O0 should stay true to the original source as much as possible. This normally wouldn't be an issue except when related to debug information, see bug9817, as DAG.Combine does not preserve debug information.
llvmbot
commented
13 years ago The reason it runs even at -O0 is that doing so speeds up compilation.
Extended Description
The DAG combiner runs even thought the Opt level is set to None. This causes problems with debug information as the DAG combiner does not preserve debug information.
For example, this IR:
define void @OpenCL_test_kernel(i32 addrspace(1) %ip) nounwind { entry: call void @llvm.dbg.value(metadata !{i32 addrspace(1) %ip}, i64 0, metadata !7), !dbg !8 %0 = call <4 x i32> @amdil_get_global_id_int() nounwind %1 = extractelement <4 x i32> %0, i32 0 call void @llvm.dbg.value(metadata !{i32 %1}, i64 0, metadata !9), !dbg !11 call void @llvm.dbg.value(metadata !12, i64 0, metadata !13), !dbg !14 %tmp2 = load i32 addrspace(1) %ip, align 4, !dbg !15 %tmp3 = add i32 0, %tmp2, !dbg !15 call void @llvm.dbg.value(metadata !{i32 %tmp3}, i64 0, metadata !13), !dbg !15 %arrayidx = getelementptr i32 addrspace(1) %ip, i32 %1, !dbg !16 store i32 %tmp3, i32 addrspace(1)* %arrayidx, align 4, !dbg !16 ret void, !dbg !17 } !llvm.dbg.sp = !{#0}
!0 = metadata !{i32 589870, i32 0, metadata !1, metadata !"OpenCL_test_kernel", metadata !"OpenCL_test_kernel", metadata !"__OpenCL_test_kernel", metadata !1, i32 2, metadata !3, i1 false, i1 true, i32 0, i32 0, i32 0, i32 0, i1 false, null} ; [ DW_TAG_subprogram ] !1 = metadata !{i32 589865, metadata !"OCL6368.tmp.cl", metadata !"E:\5CUsers\5Cmvillmow.AMD\5CAppData\5CLocal\5CTemp", metadata !2} ; [ DW_TAG_file_type ] !2 = metadata !{i32 589841, i32 0, i32 1, metadata !"OCL6368.tmp.cl", metadata !"E:\5CUsers\5Cmvillmow.AMD\5CAppData\5CLocal\5CTemp", metadata !"clc", i1 true, i1 false, metadata !"", i32 0} ; [ DW_TAG_compile_unit ] !3 = metadata !{i32 589845, metadata !1, metadata !"", metadata !1, i32 0, i64 0, i64 0, i32 0, i32 0, i32 0, metadata !4, i32 0, i32 0} ; [ DW_TAG_subroutine_type ] !4 = metadata !{null, metadata !5} !5 = metadata !{i32 589839, metadata !2, metadata !"", null, i32 0, i64 32, i64 32, i64 0, i32 0, metadata !6} ; [ DW_TAG_pointer_type ] !6 = metadata !{i32 589860, metadata !2, metadata !"unsigned int", null, i32 0, i64 32, i64 32, i64 0, i32 0, i32 7} ; [ DW_TAG_base_type ] !7 = metadata !{i32 590081, metadata !0, metadata !"ip", metadata !1, i32 1, metadata !5, i32 0} ; [ DW_TAG_arg_variable ] !8 = metadata !{i32 1, i32 42, metadata !0, null} !9 = metadata !{i32 590080, metadata !10, metadata !"gid", metadata !1, i32 3, metadata !6, i32 0} ; [ DW_TAG_auto_variable ] !10 = metadata !{i32 589835, metadata !0, i32 2, i32 1, metadata !1, i32 0} ; [ DW_TAG_lexical_block ] !11 = metadata !{i32 3, i32 41, metadata !10, null} !12 = metadata !{i32 0} !13 = metadata !{i32 590080, metadata !10, metadata !"idx", metadata !1, i32 4, metadata !6, i32 0} ; [ DW_TAG_auto_variable ] !14 = metadata !{i32 4, i32 20, metadata !10, null} !15 = metadata !{i32 5, i32 15, metadata !10, null} !16 = metadata !{i32 6, i32 18, metadata !10, null} !17 = metadata !{i32 7, i32 1, metadata !0, null} The third llvm.dbg.value is attached to %tmp3. In combine, we visit the add here, SDValue DAGCombiner::visitADD(SDNode *N), and the following transformation occurs: // fold (add x, 0) -> x if (N1C && N1C->isNullValue()) return N0;
This causes the llvm.dbg.value to be dropped and the variable does not appear in the dwarf information not allowing the variable to be inspected at that location.