Provide alignment info on LLVM external symbols

Code in CodeGenModule::GetOrCreateLLVMGlobal that sets up GlobalValue
object for LLVM external symbols has this comment:

    // FIXME: This code is overly simple and should be merged with other global
    // handling.

One part does seems to be "overly simple" currently is that this code
never sets any alignment info on the GlobalValue, so that the emitted
IR does not have any align attribute on external globals.  This can
lead to unnecessarily inefficient code generation.

This patch adds a GV->setAlignment call to set alignment info.

llvm-svn: 235396

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 17b7ddc..b30885d 100644 (file)
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1777,6 +1777,8 @@ CodeGenModule::GetOrCreateLLVMGlobal(StringRef MangledName,
     // handling.
     GV->setConstant(isTypeConstant(D->getType(), false));
 
+    GV->setAlignment(getContext().getDeclAlign(D).getQuantity());
+
     setLinkageAndVisibilityForGV(GV, D);
 
     if (D->getTLSKind()) {

diff --git a/clang/test/CodeGen/align-systemz.c b/clang/test/CodeGen/align-systemz.c
index 277492c..68a21e3 100644 (file)
--- a/clang/test/CodeGen/align-systemz.c
+++ b/clang/test/CodeGen/align-systemz.c
@@ -12,3 +12,16 @@ char c;
 struct test s;
 // CHECK-DAG: @s = common global %struct.test zeroinitializer, align 2
 
+extern char ec;
+// CHECK-DAG: @ec = external global i8, align 2
+
+extern struct test es;
+// CHECK-DAG: @es = external global %struct.test, align 2
+
+// Dummy function to make sure external symbols are used.
+void func (void)
+{
+  c = ec;
+  s = es;
+}
+