Make MachineBasicBlock::updateTerminator to update DebugLoc as well
Summary:
Currently MachineBasicBlock::updateTerminator simply drops DebugLoc for newly created branch instructions, which may cause incorrect stepping and/or imprecise sample profile data. Below is an example:
```
1 extern int bar(int x);
2
3 int foo(int *begin, int *end) {
4 int *i;
5 int ret = 0;
6 for (
7 i = begin ;
8 i != end ;
9 i++)
10 {
11 ret += bar(*i);
12 }
13 return ret;
14 }
```
Below is a bitcode of 'foo' at the end of LLVM-IR level optimizations with -O3:
```
define i32 @foo(i32* readonly %begin, i32* readnone %end) !dbg !4 {
entry:
%cmp6 = icmp eq i32* %begin, %end, !dbg !9
br i1 %cmp6, label %for.end, label %for.body.preheader, !dbg !12
for.body.preheader: ; preds = %entry
br label %for.body, !dbg !13
for.body: ; preds = %for.body.preheader, %for.body
%ret.08 = phi i32 [ %add, %for.body ], [ 0, %for.body.preheader ]
%i.07 = phi i32* [ %incdec.ptr, %for.body ], [ %begin, %for.body.preheader ]
%0 = load i32, i32* %i.07, align 4, !dbg !13, !tbaa !15
%call = tail call i32 @bar(i32 %0), !dbg !19
%add = add nsw i32 %call, %ret.08, !dbg !20
%incdec.ptr = getelementptr inbounds i32, i32* %i.07, i64 1, !dbg !21
%cmp = icmp eq i32* %incdec.ptr, %end, !dbg !9
br i1 %cmp, label %for.end.loopexit, label %for.body, !dbg !12, !llvm.loop !22
for.end.loopexit: ; preds = %for.body
br label %for.end, !dbg !24
for.end: ; preds = %for.end.loopexit, %entry
%ret.0.lcssa = phi i32 [ 0, %entry ], [ %add, %for.end.loopexit ]
ret i32 %ret.0.lcssa, !dbg !24
}
```
where
```
!12 = !DILocation(line: 6, column: 3, scope: !11)
```
. As you can see, the terminator of 'entry' block, which is a loop control branch, has a DebugLoc of line 6, column 3. Howerver, after the execution of 'MachineBlock::updateTerminator' function, which is triggered by MachineSinking pass, the DebugLoc info is dropped as below (see there's no debug-location for JNE_1):
```
bb.0.entry:
successors: %bb.4(0x30000000), %bb.1.for.body.preheader(0x50000000)
liveins: %rdi, %rsi
%6 = COPY %rsi
%5 = COPY %rdi
%8 = SUB64rr %5, %6, implicit-def %eflags, debug-location !9
JNE_1 %bb.1.for.body.preheader, implicit %eflags
```
This patch addresses this issue and make newly created branch instructions to keep debug-location info.
Reviewers: aprantl, MatzeB, craig.topper, qcolombet
Reviewed By: qcolombet
Subscribers: qcolombet, llvm-commits
Differential Revision: https://reviews.llvm.org/D29596
llvm-svn: 294976
diff --git a/llvm/test/CodeGen/X86/update-terminator-debugloc.ll b/llvm/test/CodeGen/X86/update-terminator-debugloc.ll
new file mode 100644
index 0000000..359c348
--- /dev/null
+++ b/llvm/test/CodeGen/X86/update-terminator-debugloc.ll
@@ -0,0 +1,91 @@
+; RUN: llc -stop-after=machine-sink -march=x86-64 < %s | FileCheck %s
+;
+; test code:
+; 1 extern int bar(int x);
+; 2
+; 3 int foo(int *begin, int *end) {
+; 4 int *i;
+; 5 int ret = 0;
+; 6 for (
+; 7 i = begin ;
+; 8 i != end ;
+; 9 i++)
+; 10 {
+; 11 ret += bar(*i);
+; 12 }
+; 13 return ret;
+; 14 }
+;
+; With the test code, LLVM-IR below shows that loop-control branches have a
+; debug location of line 6 (branches in entry and for.body block). Make sure that
+; these debug locations are propaged correctly to lowered instructions.
+;
+; CHECK: [[DLOC:![0-9]+]] = !DILocation(line: 6
+; CHECK-DAG: [[VREG1:%[^ ]+]] = COPY %rsi
+; CHECK-DAG: [[VREG2:%[^ ]+]] = COPY %rdi
+; CHECK: SUB64rr [[VREG2]], [[VREG1]]
+; CHECK-NEXT: JNE_1 {{.*}}, debug-location [[DLOC]]{{$}}
+; CHECK: [[VREG3:%[^ ]+]] = PHI [[VREG2]]
+; CHECK: [[VREG4:%[^ ]+]] = ADD64ri8 [[VREG3]], 4
+; CHECK: SUB64rr [[VREG1]], [[VREG4]]
+; CHECK-NEXT: JNE_1 {{.*}}, debug-location [[DLOC]]{{$}}
+; CHECK-NEXT: JMP_1 {{.*}}, debug-location [[DLOC]]{{$}}
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @foo(i32* readonly %begin, i32* readnone %end) !dbg !4 {
+entry:
+ %cmp6 = icmp eq i32* %begin, %end, !dbg !9
+ br i1 %cmp6, label %for.end, label %for.body.preheader, !dbg !12
+
+for.body.preheader: ; preds = %entry
+ br label %for.body, !dbg !13
+
+for.body: ; preds = %for.body.preheader, %for.body
+ %ret.08 = phi i32 [ %add, %for.body ], [ 0, %for.body.preheader ]
+ %i.07 = phi i32* [ %incdec.ptr, %for.body ], [ %begin, %for.body.preheader ]
+ %0 = load i32, i32* %i.07, align 4, !dbg !13, !tbaa !15
+ %call = tail call i32 @bar(i32 %0), !dbg !19
+ %add = add nsw i32 %call, %ret.08, !dbg !20
+ %incdec.ptr = getelementptr inbounds i32, i32* %i.07, i64 1, !dbg !21
+ %cmp = icmp eq i32* %incdec.ptr, %end, !dbg !9
+ br i1 %cmp, label %for.end.loopexit, label %for.body, !dbg !12, !llvm.loop !22
+
+for.end.loopexit: ; preds = %for.body
+ br label %for.end, !dbg !24
+
+for.end: ; preds = %for.end.loopexit, %entry
+ %ret.0.lcssa = phi i32 [ 0, %entry ], [ %add, %for.end.loopexit ]
+ ret i32 %ret.0.lcssa, !dbg !24
+}
+
+declare i32 @bar(i32)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1)
+!1 = !DIFile(filename: "foo.c", directory: "b/")
+!2 = !{i32 2, !"Dwarf Version", i32 4}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 3, type: !5, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, unit: !0)
+!5 = !DISubroutineType(types: !6)
+!6 = !{!7, !8, !8}
+!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!8 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !7, size: 64)
+!9 = !DILocation(line: 8, column: 9, scope: !10)
+!10 = distinct !DILexicalBlock(scope: !11, file: !1, line: 6, column: 3)
+!11 = distinct !DILexicalBlock(scope: !4, file: !1, line: 6, column: 3)
+!12 = !DILocation(line: 6, column: 3, scope: !11)
+!13 = !DILocation(line: 11, column: 18, scope: !14)
+!14 = distinct !DILexicalBlock(scope: !10, file: !1, line: 10, column: 3)
+!15 = !{!16, !16, i64 0}
+!16 = !{!"int", !17, i64 0}
+!17 = !{!"omnipotent char", !18, i64 0}
+!18 = !{!"Simple C/C++ TBAA"}
+!19 = !DILocation(line: 11, column: 14, scope: !14)
+!20 = !DILocation(line: 11, column: 11, scope: !14)
+!21 = !DILocation(line: 9, column: 8, scope: !10)
+!22 = distinct !{!22, !12, !23}
+!23 = !DILocation(line: 12, column: 3, scope: !11)
+!24 = !DILocation(line: 13, column: 3, scope: !4)