[PATCH] D157332: [clang] Make init for empty no_unique_address fields a no-op write

[Martin Storsjö via Phabricator via cfe-commits]

mstorsjo updated this revision to Diff 549575.
mstorsjo added a comment.

Move the existing comment into the new if statement, add a comment to the new if. Add a comment to the second part of the testcase, which probably is good to keep anyway.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D157332/new/

https://reviews.llvm.org/D157332

Files:
  clang/lib/CodeGen/CGCall.cpp
  clang/test/CodeGenCXX/ctor-empty-nounique.cpp


Index: clang/test/CodeGenCXX/ctor-empty-nounique.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGenCXX/ctor-empty-nounique.cpp
@@ -0,0 +1,47 @@
+// RUN: %clang_cc1 -triple x86_64-windows-gnu -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple powerpc64le-windows-gnu -emit-llvm -o - %s | FileCheck %s
+
+// An empty struct is handled as a struct with a dummy i8, on all targets.
+// Most targets treat an empty struct return value as essentially void - but
+// some don't. (Currently, at least x86_64-windows-* and powerpc64le-* don't
+// treat it as void.)
+//
+// When intializing a struct with such a no_unique_address member, make sure we
+// don't write the dummy i8 into the struct where there's no space allocated for
+// it.
+//
+// This can only be tested with targets that don't treat empty struct returns as
+// void.
+
+struct S {};
+S f();
+struct Z {
+  int x;
+  [[no_unique_address]] S y;
+  Z();
+};
+Z::Z() : x(111), y(f()) {}
+
+// CHECK: define {{.*}} @_ZN1ZC2Ev
+// CHECK: %call = call i8 @_Z1fv()
+// CHECK-NEXT: ret void
+
+
+// Check that the constructor for an empty member gets called with the right
+// 'this' pointer.
+
+struct S2 {
+  S2();
+};
+struct Z2 {
+  int x;
+  [[no_unique_address]] S2 y;
+  Z2();
+};
+Z2::Z2() : x(111) {}
+
+// CHECK: define {{.*}} @_ZN2Z2C2Ev(ptr {{.*}} %this)
+// CHECK: %this.addr = alloca ptr
+// CHECK: store ptr %this, ptr %this.addr
+// CHECK: %this1 = load ptr, ptr %this.addr
+// CHECK: call void @_ZN2S2C1Ev(ptr {{.*}} %this1)
Index: clang/lib/CodeGen/CGCall.cpp
===================================================================
--- clang/lib/CodeGen/CGCall.cpp
+++ clang/lib/CodeGen/CGCall.cpp
@@ -13,6 +13,7 @@
 
 #include "CGCall.h"
 #include "ABIInfo.h"
+#include "ABIInfoImpl.h"
 #include "CGBlocks.h"
 #include "CGCXXABI.h"
 #include "CGCleanup.h"
@@ -5777,9 +5778,13 @@
         DestIsVolatile = false;
       }
 
-      // If the value is offset in memory, apply the offset now.
-      Address StorePtr = emitAddressAtOffset(*this, DestPtr, RetAI);
-      CreateCoercedStore(CI, StorePtr, DestIsVolatile, *this);
+      // An empty record can overlap other data (if declared with no_unique_address);
+      // omit the store for such types - as there is no actual data to store.
+      if (!isEmptyRecord(getContext(), RetTy, true)) {
+        // If the value is offset in memory, apply the offset now.
+        Address StorePtr = emitAddressAtOffset(*this, DestPtr, RetAI);
+        CreateCoercedStore(CI, StorePtr, DestIsVolatile, *this);
+      }
 
       return convertTempToRValue(DestPtr, RetTy, SourceLocation());
     }


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