CodeGen: Make MachineBasicBlock::back skip to the beginning of the last bundle.

This makes front/back symmetric with begin/end, avoiding some confusion.
Added instr_front/instr_back for the old behavior, corresponding to
instr_begin/instr_end. Audited all three in-tree users of back(), all
of them look like they don't want to look inside bundles.

Fixes an assertion (PR19815) when generating debug info on mips, where a
delay slot was bundled at the end of a branch.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209580 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 78 insertions, 0 deletions

diff --git a/test/DebugInfo/Mips/delay-slot.ll b/test/DebugInfo/Mips/delay-slot.ll
new file mode 100644
index 0000000000..9bce4ba6c9
--- /dev/null
+++ b/test/DebugInfo/Mips/delay-slot.ll
@@ -0,0 +1,75 @@
+; RUN: llc -filetype=obj -O0 < %s -mtriple mips-unknown-linux-gnu | llvm-dwarfdump - | FileCheck %s
+; PR19815
+
+; Generated using clang -target mips-linux-gnu -g test.c -S -o - -flto|opt -sroa -S
+; test.c:
+;
+; int foo(int x) {
+;  if (x)
+;    return 0;
+;  return 1;
+; }
+
+; CHECK: Address            Line   Column File   ISA Discriminator Flags
+; CHECK: ------------------ ------ ------ ------ --- ------------- -------------
+; CHECK: 0x0000000000000000      1      0      1   0             0  is_stmt
+; CHECK: 0x0000000000000000      1      0      1   0             0  is_stmt prologue_end
+; CHECK: 0x0000000000000008      2      0      1   0             0  is_stmt
+; CHECK: 0x0000000000000020      3      0      1   0             0  is_stmt
+; CHECK: 0x0000000000000030      4      0      1   0             0  is_stmt
+; CHECK: 0x0000000000000040      5      0      1   0             0  is_stmt
+; CHECK: 0x0000000000000050      5      0      1   0             0  is_stmt end_sequence
+
+target datalayout = "E-m:m-p:32:32-i8:8:32-i16:16:32-i64:64-n32-S64"
+target triple = "mips--linux-gnu"
+
+; Function Attrs: nounwind
+define i32 @foo(i32 %x) #0 {
+entry:
+  call void @llvm.dbg.value(metadata !{i32 %x}, i64 0, metadata !12), !dbg !13
+  %tobool = icmp ne i32 %x, 0, !dbg !14
+  br i1 %tobool, label %if.then, label %if.end, !dbg !14
+
+if.then:                                          ; preds = %entry
+  br label %return, !dbg !16
+
+if.end:                                           ; preds = %entry
+  br label %return, !dbg !17
+
+return:                                           ; preds = %if.end, %if.then
+  %retval.0 = phi i32 [ 0, %if.then ], [ 1, %if.end ]
+  ret i32 %retval.0, !dbg !18
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.declare(metadata, metadata) #1
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, i64, metadata) #1
+
+attributes #0 = { nounwind }
+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 ", i1 false, metadata !"", i32 0, metadata !2, metadata !2, metadata !3, metadata !2, metadata !2, metadata !"", i32 1} ; [ DW_TAG_compile_unit ] [/tmp/test.c] [DW_LANG_C99]
+!1 = metadata !{metadata !"test.c", metadata !"/tmp"}
+!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, i32 (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 ] [/tmp/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 !{metadata !8, 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 2, metadata !"Debug Info Version", i32 1}
+!11 = metadata !{metadata !"clang version 3.5.0"}
+!12 = metadata !{i32 786689, metadata !4, metadata !"x", metadata !5, i32 16777217, metadata !8, i32 0, i32 0} ; [ DW_TAG_arg_variable ] [x] [line 1]
+!13 = metadata !{i32 1, i32 0, metadata !4, null}
+!14 = metadata !{i32 2, i32 0, metadata !15, null}
+!15 = metadata !{i32 786443, metadata !1, metadata !4, i32 2, i32 0, i32 0, i32 0} ; [ DW_TAG_lexical_block ] [/tmp/test.c]
+!16 = metadata !{i32 3, i32 0, metadata !15, null}
+!17 = metadata !{i32 4, i32 0, metadata !4, null}
+!18 = metadata !{i32 5, i32 0, metadata !4, null}
diff --git a/test/DebugInfo/Mips/lit.local.cfg b/test/DebugInfo/Mips/lit.local.cfg
new file mode 100644
index 0000000000..88262fb1d3
--- /dev/null
+++ b/test/DebugInfo/Mips/lit.local.cfg
@@ -0,0 +1,3 @@
+targets = set(config.root.targets_to_build.split())
+if not 'Mips' in targets:
+    config.unsupported = True