[PATCH] D46685: [CodeGen] Disable structor optimizations at -O0

[Pavel Labath via Phabricator via cfe-commits]

labath updated this revision to Diff 146309.
labath added a comment.

Yes we can do that. Only the RAUW optimization is nasty, I've checked that the
debugger is able to use the alias with no problem.

Updated the patch the reflect that.


Repository:
  rC Clang

https://reviews.llvm.org/D46685

Files:
  lib/CodeGen/ItaniumCXXABI.cpp
  test/CodeGenCXX/ctor-dtor-alias.cpp
  test/CodeGenCXX/float16-declarations.cpp


Index: test/CodeGenCXX/float16-declarations.cpp
===================================================================
--- test/CodeGenCXX/float16-declarations.cpp
+++ test/CodeGenCXX/float16-declarations.cpp
@@ -103,7 +103,7 @@
 
   C1 c1(f1l);
 // CHECK-DAG:  [[F1L:%[a-z0-9]+]] = load half, half* %{{.*}}, align 2
-// CHECK-DAG:  call void @_ZN2C1C2EDF16_(%class.C1* %{{.*}}, half %{{.*}})
+// CHECK-DAG:  call void @_ZN2C1C1EDF16_(%class.C1* %{{.*}}, half %{{.*}})
 
   S1<_Float16> s1 = { 132.f16 };
 // CHECK-DAG: @_ZZ4mainE2s1 = private unnamed_addr constant %struct.S1 { half 0xH5820 }, align 2
Index: test/CodeGenCXX/ctor-dtor-alias.cpp
===================================================================
--- test/CodeGenCXX/ctor-dtor-alias.cpp
+++ test/CodeGenCXX/ctor-dtor-alias.cpp
@@ -77,11 +77,12 @@
   // CHECK1: call i32 @__cxa_atexit{{.*}}_ZN5test41AD2Ev
   // CHECK1: define linkonce_odr void @_ZN5test41AD2Ev({{.*}} comdat align
 
-  // test that we don't do this optimization at -O0 so that the debugger can
-  // see both destructors.
+  // test that we don't do this optimization at -O0 and call the complete
+  // destructor for B instead. This enables the debugger to see both
+  // destructors.
+  // NOOPT: @_ZN5test41BD1Ev = linkonce_odr alias void {{.*}} @_ZN5test41BD2Ev
   // NOOPT: define internal void @__cxx_global_var_init.2()
-  // NOOPT: call i32 @__cxa_atexit{{.*}}@_ZN5test41BD2Ev
-  // NOOPT: define linkonce_odr void @_ZN5test41BD2Ev({{.*}} comdat align
+  // NOOPT: call i32 @__cxa_atexit{{.*}}@_ZN5test41BD1Ev
   struct A {
     virtual ~A() {}
   };
Index: lib/CodeGen/ItaniumCXXABI.cpp
===================================================================
--- lib/CodeGen/ItaniumCXXABI.cpp
+++ lib/CodeGen/ItaniumCXXABI.cpp
@@ -3625,12 +3625,16 @@
   }
   llvm::GlobalValue::LinkageTypes Linkage = CGM.getFunctionLinkage(AliasDecl);
 
-  if (llvm::GlobalValue::isDiscardableIfUnused(Linkage))
-    return StructorCodegen::RAUW;
-
-  // FIXME: Should we allow available_externally aliases?
-  if (!llvm::GlobalAlias::isValidLinkage(Linkage))
-    return StructorCodegen::RAUW;
+  // Only use RAUW in optimized code, as it makes the complete structor symbol
+  // disappear completely, which degrades debugging experience.
+  if (CGM.getCodeGenOpts().OptimizationLevel > 0) {
+    if (llvm::GlobalValue::isDiscardableIfUnused(Linkage))
+      return StructorCodegen::RAUW;
+
+    // FIXME: Should we allow available_externally aliases?
+    if (!llvm::GlobalAlias::isValidLinkage(Linkage))
+      return StructorCodegen::RAUW;
+  }
 
   if (llvm::GlobalValue::isWeakForLinker(Linkage)) {
     // Only ELF and wasm support COMDATs with arbitrary names (C5/D5).


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