[clang] [clang codegen] Delete unnecessary GEP cleanup code. (PR #90303)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-codegen

Author: Eli Friedman (efriedma-quic)

<details>
<summary>Changes</summary>

There's some code in AggExprEmitter::VisitCXXParenListOrInitListExpr to try to do early cleanup for GEPs for fields that aren't accessed. But it's unlikely to actually save significant compile-time, and it's subtly wrong in cases where EmitLValueForFieldInitialization() doesn't create a GEP.  So just delete the code.

Fixes #<!-- -->88077. Fixes #<!-- -->89547.

---
Full diff: https://github.com/llvm/llvm-project/pull/90303.diff


2 Files Affected:

- (modified) clang/lib/CodeGen/CGExprAgg.cpp (-10) 
- (modified) clang/test/CodeGenCXX/no-unique-address.cpp (+25) 


``````````diff
diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index 355fec42be4489..61db6293ed6a1e 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -1811,7 +1811,6 @@ void AggExprEmitter::VisitCXXParenListOrInitListExpr(
     // Push a destructor if necessary.
     // FIXME: if we have an array of structures, all explicitly
     // initialized, we can end up pushing a linear number of cleanups.
-    bool pushedCleanup = false;
     if (QualType::DestructionKind dtorKind
           = field->getType().isDestructedType()) {
       assert(LV.isSimple());
@@ -1819,17 +1818,8 @@ void AggExprEmitter::VisitCXXParenListOrInitListExpr(
         CGF.pushDestroy(EHCleanup, LV.getAddress(CGF), field->getType(),
                         CGF.getDestroyer(dtorKind), false);
         addCleanup(CGF.EHStack.stable_begin());
-        pushedCleanup = true;
       }
     }
-
-    // If the GEP didn't get used because of a dead zero init or something
-    // else, clean it up for -O0 builds and general tidiness.
-    if (!pushedCleanup && LV.isSimple())
-      if (llvm::GetElementPtrInst *GEP =
-              dyn_cast<llvm::GetElementPtrInst>(LV.emitRawPointer(CGF)))
-        if (GEP->use_empty())
-          GEP->eraseFromParent();
   }
 
   // Deactivate all the partial cleanups in reverse order, which
diff --git a/clang/test/CodeGenCXX/no-unique-address.cpp b/clang/test/CodeGenCXX/no-unique-address.cpp
index 7b4bbbf2a05d51..82532c5e1be82a 100644
--- a/clang/test/CodeGenCXX/no-unique-address.cpp
+++ b/clang/test/CodeGenCXX/no-unique-address.cpp
@@ -101,3 +101,28 @@ struct HasZeroSizedFieldWithNonTrivialInit {
 HasZeroSizedFieldWithNonTrivialInit testHasZeroSizedFieldWithNonTrivialInit = {.a = 1};
 // CHECK-LABEL: define {{.*}}cxx_global_var_init
 // CHECK: call {{.*}}@_ZN14NonTrivialInitC1Ev({{.*}}@testHasZeroSizedFieldWithNonTrivialInit
+
+void *operator new(unsigned long, void *);
+template <class Ty>
+struct _box {
+  [[no_unique_address]] Ty _value;
+};
+// Make sure this doesn't crash.
+// CHECK-LABEL: define {{.*}}placement_new_struct
+void placement_new_struct() {
+  struct set_value_t {};
+
+  // GH88077
+  struct _tuple : _box<set_value_t>, _box<int> {};
+
+  int _storage[1];
+  new (_storage) _tuple{};
+
+  // GH89547
+  struct _tuple2 {
+    _box<set_value_t> a;
+  };
+
+  int _storage2[1];
+  new (_storage2) _tuple2{};
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/90303