[StripDeadDebugInfo] Drop dead CUs for const global expression

Compile units are not left explicitly if they have const global
expression.  They should be left if that const global is used in a
function that is contained in extracted module.

Signed-off-by: Mikhail Lychkov <[email protected]>

Differential Revision: https://reviews.llvm.org/D131179

Author: bader

llvm/lib/Transforms/IPO/StripSymbols.cpp

@@ -30,12 +30,18 @@
 #include "llvm/IR/PassManager.h"
 #include "llvm/IR/TypeFinder.h"
 #include "llvm/IR/ValueSymbolTable.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Transforms/IPO.h"
 #include "llvm/Transforms/IPO/StripSymbols.h"
 #include "llvm/Transforms/Utils/Local.h"
 
 using namespace llvm;
 
+static cl::opt<bool>
+    StripGlobalConstants("strip-global-constants", cl::init(false), cl::Hidden,
+                         cl::desc("Removes debug compile units which reference "
+                                  "to non-existing global constants"));
+
 /// OnlyUsedBy - Return true if V is only used by Usr.
 static bool OnlyUsedBy(Value *V, Value *Usr) {
   for (User *U : V->users())
@@ -216,7 +222,8 @@ static bool stripDeadDebugInfoImpl(Module &M) {
     // Create our live global variable list.
     bool GlobalVariableChange = false;
     for (auto *DIG : DIC->getGlobalVariables()) {
-      if (DIG->getExpression() && DIG->getExpression()->isConstant())
+      if (DIG->getExpression() && DIG->getExpression()->isConstant() &&
+          !StripGlobalConstants)
         LiveGVs.insert(DIG);
 
       // Make sure we only visit each global variable only once.

llvm/test/Transforms/StripSymbols/strip-cu-with-const-gve.ll

@@ -0,0 +1,61 @@
+; This test checks that strip-dead-debug-info pass deletes debug compile units
+; if global constants from those units are absent in the module.
+
+; RUN: opt -passes='strip-dead-debug-info,verify' -strip-global-constants %s -S | FileCheck %s
+
+; CHECK: !llvm.dbg.cu = !{!{{[0-9]+}}, !{{[0-9]+}}}
+; CHECK-COUNT-2: !DICompileUnit
+
+;target datalayout = "e-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024-n8:16:32:64"
+;target triple = "spir64-unknown-unknown"
+
+; Function Attrs: convergent nounwind
+define void @dev_func1() #0 !dbg !16 {
+  %1 = call i32 @dev_subfunc1(i32 0) #1, !dbg !19
+  ret void, !dbg !20
+}
+
+; Function Attrs: convergent nounwind
+define i32 @dev_subfunc1(i32 %0) #0 !dbg !21 {
+  ret i32 %0, !dbg !24
+}
+
+; Function Attrs: convergent nounwind
+define void @dev_func2() #0 !dbg !25 {
+  ret void, !dbg !26
+}
+
+attributes #0 = { convergent nounwind }
+attributes #1 = { convergent }
+
+!llvm.dbg.cu = !{!0, !8, !10}
+!llvm.module.flags = !{!15}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !3, imports: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "dev_func1.cpp", directory: "/home/usr/test")
+!2 = !{}
+!3 = !{!4}
+!4 = !DIGlobalVariableExpression(var: !5, expr: !DIExpression(DW_OP_constu, 0, DW_OP_stack_value))
+!5 = distinct !DIGlobalVariable(name: "ZERO", scope: !1, file: !1, line: 32, type: !6, isLocal: true, isDefinition: true)
+!6 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !7)
+!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!8 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !9, isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, imports: !2, splitDebugInlining: false, nameTableKind: None)
+!9 = !DIFile(filename: "dev_func2.cpp", directory: "/home/usr/test")
+!10 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !11, isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !12, imports: !2, splitDebugInlining: false, nameTableKind: None)
+!11 = !DIFile(filename: "file3.cpp", directory: "/home/usr/test")
+!12 = !{!13}
+!13 = !DIGlobalVariableExpression(var: !14, expr: !DIExpression(DW_OP_constu, 0, DW_OP_stack_value))
+!14 = distinct !DIGlobalVariable(name: "ZERO", scope: !11, file: !11, line: 145, type: !6, isLocal: true, isDefinition: true)
+!15 = !{i32 2, !"Debug Info Version", i32 3}
+!16 = distinct !DISubprogram(name: "dev_func1", linkageName: "dev_func1", scope: !1, file: !1, line: 22, type: !17, scopeLine: 22, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!17 = !DISubroutineType(types: !18)
+!18 = !{null}
+!19 = !DILocation(line: 12, column: 1, scope: !16)
+!20 = !DILocation(line: 29, column: 5, scope: !16)
+!21 = distinct !DISubprogram(name: "dev_subfunc1", linkageName: "dev_subfunc1", scope: !1, file: !1, line: 42, type: !22, scopeLine: 42, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!22 = !DISubroutineType(types: !23)
+!23 = !{!7, !7}
+!24 = !DILocation(line: 5, column: 1, scope: !21)
+!25 = distinct !DISubprogram(name: "dev_func2", linkageName: "dev_func2", scope: !9, file: !9, line: 22, type: !17, scopeLine: 22, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !8, retainedNodes: !2)
+!26 = !DILocation(line: 29, column: 5, scope: !25)
+