[PATCH] Fix for PR 19261: generate unconditional branches with "-O0 -fast-isel=false"
Reid Kleckner
rnk at google.com
Thu Mar 27 09:29:34 PDT 2014
lgtm
On Thu, Mar 27, 2014 at 9:14 AM, Daniil Fukalov <daniil.fukalov at amd.com>wrote:
> dfukalov added you to the CC list for the revision "Fix for PR 19261:
> generate unconditional branches with "-O0 -fast-isel=false"".
>
> Hi timurrrr,
>
> Fix for PR 19261:
>
> llc doesn't generate nodes for unconditional fall-through branches for
> targets without FastISel implementation (X86 has it, but can be disabled by
> "-fast-isel=false") in SelectionDAGBuilder::visitBr(). So for line 4 in the
> following testcase
>
> 1: void foo(int i){
> 2: switch(i){
> 3: default:
> 4: break;
> 5: }
> 6: return;
> 7: }
>
> there is no corresponding line in .debug_line section, and a debugger
> cannot set a breakpoint at line 4.
>
> http://llvm-reviews.chandlerc.com/D3203
>
> Files:
> lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
> test/DebugInfo/uncond_br_O0.ll
>
> Index: lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
> ===================================================================
> --- lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
> +++ lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
> @@ -1574,8 +1574,9 @@
> // Update machine-CFG edges.
> BrMBB->addSuccessor(Succ0MBB);
>
> - // If this is not a fall-through branch, emit the branch.
> - if (Succ0MBB != NextBlock)
> + // If this is not a fall-through branch or optimizations are switched
> off,
> + // emit the branch.
> + if (Succ0MBB != NextBlock || TM.getOptLevel() == CodeGenOpt::None)
> DAG.setRoot(DAG.getNode(ISD::BR, getCurSDLoc(),
> MVT::Other, getControlRoot(),
> DAG.getBasicBlock(Succ0MBB)));
> Index: test/DebugInfo/uncond_br_O0.ll
> ===================================================================
> --- test/DebugInfo/uncond_br_O0.ll
> +++ test/DebugInfo/uncond_br_O0.ll
> @@ -0,0 +1,68 @@
> +; REQUIRES: object-emission
> +; PR 19261
> +
> +; RUN: %llc_dwarf -fast-isel=false -O0 -filetype=obj < %s > %t
> +; RUN: llvm-dwarfdump %t | FileCheck %s
> +
> +; CHECK: {{0x[0-9a-f]+}} 1 0 1 0 0 is_stmt
> +; CHECK-NEXT: {{0x[0-9a-f]+}} 2 0 1 0 0
> is_stmt
> +; CHECK-NEXT: {{0x[0-9a-f]+}} 4 0 1 0 0
> is_stmt
> +
> +; IR generated from clang -O0 -g with the following source:
> +;void foo(int i){
> +; switch(i){
> +; default:
> +; break;
> +; }
> +; return;
> +;}
> +
> +; ModuleID = 'test.bc'
> +target datalayout = "e-m:w-p:32:32-i64:64-f80:32-n8:16:32-S32"
> +target triple = "i686-pc-win32"
> +
> +; Function Attrs: nounwind
> +define void @foo(i32 %i) #0 {
> +entry:
> + %i.addr = alloca i32, align 4
> + store i32 %i, i32* %i.addr, align 4
> + call void @llvm.dbg.declare(metadata !{i32* %i.addr}, metadata !12),
> !dbg !13
> + %0 = load i32* %i.addr, align 4, !dbg !14
> + switch i32 %0, label %sw.default [
> + ], !dbg !14
> +
> +sw.default: ; preds = %entry
> + br label %sw.epilog, !dbg !15
> +
> +sw.epilog: ; preds = %sw.default
> + ret void, !dbg !17
> +}
> +
> +; Function Attrs: nounwind readnone
> +declare void @llvm.dbg.declare(metadata, metadata) #1
> +
> +attributes #0 = { nounwind "less-precise-fpmad"="false"
> "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf"
> "no-infs-fp-math"="false" "no-nans-fp-math"="false"
> "stack-protector-buffer-size"="8" "unsafe-fp-math"="false"
> "use-soft-float"="false" }
> +attributes #1 = { nounwind readnone }
> +
> +!llvm.dbg.cu = !{!0}
> +!llvm.module.flags = !{!9, !10}
> +!llvm.ident = !{!11}
> +
> +!0 = metadata !{i32 786449, metadata !1, i32 12, metadata !"clang version
> 3.5.0 (204712)", i1 false, metadata !"", i32 0, metadata !2, metadata !2,
> metadata !3, metadata !2, metadata !2, metadata !"", i32 1} ; [
> DW_TAG_compile_unit ] [D:\work\EPRs\396363/test.c] [DW_LANG_C99]
> +!1 = metadata !{metadata !"test.c", metadata !"D:\5Cwork\5CEPRs\5C396363"}
> +!2 = metadata !{}
> +!3 = metadata !{metadata !4}
> +!4 = metadata !{i32 786478, metadata !1, metadata !5, metadata !"foo",
> metadata !"foo", metadata !"", i32 1, metadata !6, i1 false, i1 true, i32
> 0, i32 0, null, i32 256, i1 false, void (i32)* @foo, null, null, metadata
> !2, i32 1} ; [ DW_TAG_subprogram ] [line 1] [def] [foo]
> +!5 = metadata !{i32 786473, metadata !1} ; [ DW_TAG_file_type ]
> [D:\work\EPRs\396363/test.c]
> +!6 = metadata !{i32 786453, i32 0, null, metadata !"", i32 0, i64 0, i64
> 0, i64 0, i32 0, null, metadata !7, i32 0, null, null, null} ; [
> DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
> +!7 = metadata !{null, metadata !8}
> +!8 = metadata !{i32 786468, null, null, metadata !"int", i32 0, i64 32,
> i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ] [int] [line 0, size 32,
> align 32, offset 0, enc DW_ATE_signed]
> +!9 = metadata !{i32 2, metadata !"Dwarf Version", i32 4}
> +!10 = metadata !{i32 1, metadata !"Debug Info Version", i32 1}
> +!11 = metadata !{metadata !"clang version 3.5.0 (204712)"}
> +!12 = metadata !{i32 786689, metadata !4, metadata !"i", metadata !5, i32
> 16777217, metadata !8, i32 0, i32 0} ; [ DW_TAG_arg_variable ] [i] [line 1]
> +!13 = metadata !{i32 1, i32 0, metadata !4, null}
> +!14 = metadata !{i32 2, i32 0, metadata !4, null}
> +!15 = metadata !{i32 4, i32 0, metadata !16, null}
> +!16 = metadata !{i32 786443, metadata !1, metadata !4, i32 2, i32 0, i32
> 0, i32 0} ; [ DW_TAG_lexical_block ] [D:\work\EPRs\396363/test.c]
> +!17 = metadata !{i32 6, i32 0, metadata !4, null}
>
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