Fix for PR 19261: generate unconditional branches with "-O0 -fast-isel=false"

[dfukalov]

Summary

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.

[timurrrr]

Unfortunately, I'm not familiar with this code.

[rnk]

lgtm

[dfukalov]

ping?

[rnk]

lgtm2

[echristo]

Sorry, lost it in my review queue.

LGTM. Please commit.

[dfukalov]

I have no commit access... Reid would you please commit it? Thanks in advance.

[echristo]

I've gone ahead and committed it as:

A test/DebugInfo/unconditional-branch.ll
M lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
r205529

I changed the name of the test file and removed the X86 specific bits.
It still passes on my machines, but I'll watch the bots and make sure.

Thanks!

-eric

[dfukalov]

thank you!

[dfukalov]

committed in r205529

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

     // 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)));

test/DebugInfo/uncond_br_O0.ll

+; 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}