GlobalDCE: Teach isEmptyFunction() to ignore debug intrinsics.

This fixes PR39669.
https://bugs.llvm.org/show_bug.cgi?id=39669

llvm-svn: 347065

2 files changed, 34 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/IPO/GlobalDCE.cpp b/llvm/lib/Transforms/IPO/GlobalDCE.cpp
index c77ea04102c..34de8743336 100644
--- a/llvm/lib/Transforms/IPO/GlobalDCE.cpp
+++ b/llvm/lib/Transforms/IPO/GlobalDCE.cpp
@@ -19,6 +19,7 @@
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Pass.h"
 #include "llvm/Transforms/IPO.h"
@@ -75,13 +76,17 @@ ModulePass *llvm::createGlobalDCEPass() {
   return new GlobalDCELegacyPass();
 }
 
-/// Returns true if F contains only a single "ret" instruction.
+/// Returns true if F is effectively empty.
 static bool isEmptyFunction(Function *F) {
   BasicBlock &Entry = F->getEntryBlock();
-  if (Entry.size() != 1 || !isa<ReturnInst>(Entry.front()))
-    return false;
-  ReturnInst &RI = cast<ReturnInst>(Entry.front());
-  return RI.getReturnValue() == nullptr;
+  for (auto &I : Entry) {
+    if (isa<DbgInfoIntrinsic>(I))
+      continue;
+    if (auto *RI = dyn_cast<ReturnInst>(&I))
+      return !RI->getReturnValue();
+    break;
+  }
+  return false;
 }
 
 /// Compute the set of GlobalValue that depends from V.
diff --git a/llvm/test/Transforms/GlobalDCE/global_ctors.ll b/llvm/test/Transforms/GlobalDCE/global_ctors.ll
index 91bb9ab7f6b..bd1a97e6ec2 100644
--- a/llvm/test/Transforms/GlobalDCE/global_ctors.ll
+++ b/llvm/test/Transforms/GlobalDCE/global_ctors.ll
@@ -1,14 +1,37 @@
 ; RUN: opt -S -globaldce < %s | FileCheck %s
 
+; Test that the presence of debug intrinsics isn't affecting GlobalDCE.
 ; CHECK: @llvm.global_ctors = appending global [1 x { i32, void ()* }] [{ i32, void ()* } { i32 65535, void ()* @_notremovable }]
 ; CHECK-NOT: @_GLOBAL__I_a
 
 declare void @_notremovable()
 
-@llvm.global_ctors = appending global [2 x { i32, void ()* }] [{ i32, void ()* } { i32 65535, void ()* @_GLOBAL__I_a }, { i32, void ()* } { i32 65535, void ()* @_notremovable }]
+@llvm.global_ctors = appending global [3 x { i32, void ()* }] [{ i32, void ()* } { i32 65535, void ()* @_GLOBAL__I_a }, { i32, void ()* } { i32 65535, void ()* @_GLOBAL__I_b }, { i32, void ()* } { i32 65535, void ()* @_notremovable }]
+
+@x = internal unnamed_addr constant i8 undef, align 1
 
 ; Function Attrs: nounwind readnone
 define internal void @_GLOBAL__I_a() #1 section "__TEXT,__StaticInit,regular,pure_instructions" {
 entry:
   ret void
 }
+
+; Function Attrs: nounwind readnone
+define internal void @_GLOBAL__I_b() #1 section "__TEXT,__StaticInit,regular,pure_instructions" {
+entry:
+  tail call void @llvm.dbg.value(metadata i8* @x, metadata !4, metadata !DIExpression(DW_OP_deref, DW_OP_constu, 0, DW_OP_swap, DW_OP_xderef)), !dbg !5
+  ret void
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.module.flags = !{!0}
+!llvm.dbg.cu = !{!1}
+
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+!1 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !2, emissionKind: FullDebug)
+!2 = !DIFile(filename: "filename", directory: "directory")
+!3 = distinct !DISubprogram(name: "h1", unit: !1)
+!4 = !DILocalVariable(name: "b", arg: 1, scope: !3)
+!5 = !DILocation(scope: !3)