[PATCH] D24164: Remove debug info when hoisting instruction from then/else branch.

[Dehao Chen via llvm-commits]

danielcdh created this revision.
danielcdh added reviewers: davidxl, dblaikie.
danielcdh added a subscriber: llvm-commits.

The hoisted instruction is executed speculatively. It could affect the debugging experience as user would see gdb go into code that may not be expected to execute. It will also affect sample profile accuracy by assigning incorrect frequency to source within then/else branch.

https://reviews.llvm.org/D24164

Files:
  lib/Transforms/Utils/SimplifyCFG.cpp
  test/Transforms/SimplifyCFG/remove-debug.ll

Index: test/Transforms/SimplifyCFG/remove-debug.ll
===================================================================
--- /dev/null
+++ test/Transforms/SimplifyCFG/remove-debug.ll
@@ -0,0 +1,81 @@
+; RUN: opt < %s -simplifycfg -S | FileCheck %s
+
+; CHECK: line: 6
+; CHECK-NOT: line: 7
+; CHECK: line: 8
+; CHECK: line: 9
+; CHECK-NOT: line: 10
+; CHECK: line: 11
+
+; Checks if the debug info for hoisted "x = i" is removed
+; int x;
+; void bar();
+; void baz();
+;
+; void foo(int i) {
+;   if (i == 0) {
+;     x = i;
+;     bar();
+;   } else {
+;     x = i;
+;     baz();
+;   }
+; }
+
+target triple = "x86_64-unknown-linux-gnu"
+
+ at x = global i32 0, align 4
+
+; Function Attrs: uwtable
+define void @_Z3fooi(i32) #0 !dbg !6 {
+  %2 = alloca i32, align 4
+  store i32 %0, i32* %2, align 4, !tbaa !8
+  %3 = load i32, i32* %2, align 4, !dbg !12, !tbaa !8
+  %4 = icmp eq i32 %3, 0, !dbg !13
+  br i1 %4, label %5, label %7, !dbg !12
+
+; <label>:5:
+  %6 = load i32, i32* %2, align 4, !dbg !14, !tbaa !8
+  store i32 %6, i32* @x, align 4, !dbg !15, !tbaa !8
+  call void @_Z3barv(), !dbg !16
+  br label %9, !dbg !17
+
+; <label>:7:
+  %8 = load i32, i32* %2, align 4, !dbg !18, !tbaa !8
+  store i32 %8, i32* @x, align 4, !dbg !19, !tbaa !8
+  call void @_Z3bazv(), !dbg !20
+  br label %9
+
+; <label>:9:
+  ret void, !dbg !21
+}
+
+declare void @_Z3barv() #1
+
+declare void @_Z3bazv() #1
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1)
+!1 = !DIFile(filename: "a", directory: "b/")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{}
+!6 = distinct !DISubprogram(unit: !0)
+!7 = !DISubroutineType(types: !2)
+!8 = !{!9, !9, i64 0}
+!9 = !{!"int", !10, i64 0}
+!10 = !{!"omnipotent char", !11, i64 0}
+!11 = !{!"Simple C++ TBAA"}
+!12 = !DILocation(line: 6, column: 7, scope: !6)
+!13 = !DILocation(line: 6, column: 9, scope: !6)
+!14 = !DILocation(line: 7, column: 9, scope: !6)
+!15 = !DILocation(line: 7, column: 7, scope: !6)
+!16 = !DILocation(line: 8, column: 5, scope: !6)
+!17 = !DILocation(line: 9, column: 3, scope: !6)
+!18 = !DILocation(line: 10, column: 9, scope: !6)
+!19 = !DILocation(line: 10, column: 7, scope: !6)
+!20 = !DILocation(line: 11, column: 5, scope: !6)
+!21 = !DILocation(line: 13, column: 1, scope: !6)
Index: lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyCFG.cpp
+++ lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1245,6 +1245,9 @@
     I2->eraseFromParent();
     Changed = true;
 
+    if (!isa<CallInst>(I1) &&  I1->getDebugLoc() != I2->getDebugLoc())
+      I1->setDebugLoc(nullptr);
+ 
     I1 = &*BB1_Itr++;
     I2 = &*BB2_Itr++;
     // Skip debug info if it is not identical.


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