From e5914dd1a35ed714e6235157db5f4d72f78319fa Mon Sep 17 00:00:00 2001
From: Dehao Chen <dehao@google.com>
Date: Wed, 16 Aug 2017 01:55:26 +0000
Subject: [PATCH] Merge debug info when hoist then-else code to if.

Summary: When we move then-else code to if, we need to merge its debug info, otherwise the hoisted instruction may have inaccurate debug info attached.

Reviewers: aprantl, probinson, dblaikie, echristo, loladiro

Reviewed By: aprantl

Subscribers: sanjoy, llvm-commits

Differential Revision: https://reviews.llvm.org/D36778

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310985 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/SimplifyCFG.cpp       |  2 ++
 test/Transforms/SimplifyCFG/min_dbginfo.ll | 39 ++++++++++++++++++++++
 2 files changed, 41 insertions(+)
 create mode 100644 test/Transforms/SimplifyCFG/min_dbginfo.ll

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 1204a94a32a..55897cc507b 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1336,6 +1336,8 @@ HoistTerminator:
     I2->replaceAllUsesWith(NT);
     NT->takeName(I1);
   }
+  NT->setDebugLoc(DILocation::getMergedLocation(
+      I1->getDebugLoc(), I2->getDebugLoc()));
 
   IRBuilder<NoFolder> Builder(NT);
   // Hoisting one of the terminators from our successor is a great thing.
diff --git a/test/Transforms/SimplifyCFG/min_dbginfo.ll b/test/Transforms/SimplifyCFG/min_dbginfo.ll
new file mode 100644
index 00000000000..ee8a87dae31
--- /dev/null
+++ b/test/Transforms/SimplifyCFG/min_dbginfo.ll
@@ -0,0 +1,39 @@
+; RUN: opt < %s -simplifycfg -S | FileCheck %s
+
+; Checks if the debug info is removed for the "select" instruction.
+; CHECK: cmp {{.*}} !dbg
+; CHECK-NOT: select {{.*}} !dbg
+define i32 @min(i32 %a, i32 %b) {
+entry:
+  %cmp = icmp slt i32 %a, %b, !dbg !9
+  br i1 %cmp, label %if.then, label %if.else, !dbg !10
+
+if.then:
+  br label %return, !dbg !11
+
+if.else:
+  br label %return, !dbg !12
+
+return:
+  %retval.0 = phi i32 [ %a, %if.then ], [ %b, %if.else ]
+  ret i32 %retval.0, !dbg !13
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 6.0.0 (trunk 310792)", isOptimized: true, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2)
+!1 = !DIFile(filename: "min.cc", directory: "/")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 6.0.0 (trunk 310792)"}
+!7 = distinct !DISubprogram(name: "min", scope: !1, file: !1, line: 3, type: !8, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !2)
+!8 = !DISubroutineType(types: !2)
+!9 = !DILocation(line: 4, column: 8, scope: !7)
+!10 = !DILocation(line: 4, column: 6, scope: !7)
+!11 = !DILocation(line: 5, column: 3, scope: !7)
+!12 = !DILocation(line: 7, column: 3, scope: !7)
+!13 = !DILocation(line: 9, column: 1, scope: !7)
-- 
2.50.1