Fix __alignof__ of global variables on SystemZ

SystemZ prefers to align all global variables to two bytes, which is
implemented by setting the TargetInfo member MinGlobalAlign.

However, for compatibility with existing compilers this should *not*
change the ABI alignment value as retrieved via __alignof__, which
it currently does.

This patch fixes the issue by having ASTContext::getDeclAlign ignore
the MinGlobalAlign setting in the ForAlignof case.

Since SystemZ is the only platform setting MinGlobalAlign, this should
cause no change for any other target.

llvm-svn: 235395

3 files changed, 32 insertions, 1 deletions

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 899f8c5ff52..c54a006d26a 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -1335,7 +1335,7 @@ CharUnits ASTContext::getDeclAlign(const Decl *D, bool ForAlignof) const {
       }
       Align = std::max(Align, getPreferredTypeAlign(T.getTypePtr()));
       if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
-        if (VD->hasGlobalStorage())
+        if (VD->hasGlobalStorage() && !ForAlignof)
           Align = std::max(Align, getTargetInfo().getMinGlobalAlign());
       }
     }
diff --git a/clang/test/CodeGen/align-systemz.c b/clang/test/CodeGen/align-systemz.c
new file mode 100644
index 00000000000..277492c0601
--- /dev/null
+++ b/clang/test/CodeGen/align-systemz.c
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -triple s390x-linux-gnu -emit-llvm %s -o - | FileCheck %s
+
+// SystemZ prefers to align all global variables to two bytes.
+
+struct test {
+   signed char a;
+};
+
+char c;
+// CHECK-DAG: @c = common global i8 0, align 2
+
+struct test s;
+// CHECK-DAG: @s = common global %struct.test zeroinitializer, align 2
+
diff --git a/clang/test/Sema/align-systemz.c b/clang/test/Sema/align-systemz.c
new file mode 100644
index 00000000000..6928549de11
--- /dev/null
+++ b/clang/test/Sema/align-systemz.c
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -triple s390x-linux-gnu -fsyntax-only -verify %s
+// expected-no-diagnostics
+
+// SystemZ prefers to align all global variables to two bytes,
+// but this should *not* be reflected in the ABI alignment as
+// retrieved via __alignof__.
+
+struct test {
+  signed char a;
+};
+
+char c;
+struct test s;
+
+int chk1[__alignof__(c) == 1 ? 1 : -1];
+int chk2[__alignof__(s) == 1 ? 1 : -1];
+