Update enforceKnownAlignment after the isWeakForLinker semantic change

Previously we would refrain from attempting to increase the linkage of
available_externally globals because they were considered weak for the
linker. Now they are treated more like a declaration instead of a weak
definition.

This was causing SSE alignment faults in Chromuim, when some code
assumed it could increase the alignment of a dllimported global that it
didn't control.  http://crbug.com/509256

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242091 91177308-0d34-0410-b5e6-96231b3b80d8

Author: rnk

lib/Transforms/Utils/Local.cpp

@@ -900,13 +900,10 @@ static unsigned enforceKnownAlignment(Value *V, unsigned Align,
 
   if (auto *GO = dyn_cast<GlobalObject>(V)) {
     // If there is a large requested alignment and we can, bump up the alignment
-    // of the global.
-    if (GO->isDeclaration())
-      return Align;
-    // If the memory we set aside for the global may not be the memory used by
-    // the final program then it is impossible for us to reliably enforce the
-    // preferred alignment.
-    if (GO->isWeakForLinker())
+    // of the global.  If the memory we set aside for the global may not be the
+    // memory used by the final program then it is impossible for us to reliably
+    // enforce the preferred alignment.
+    if (!GO->isStrongDefinitionForLinker())
       return Align;
 
     if (GO->getAlignment() >= PrefAlign)

test/Transforms/InstCombine/align-external.ll

@@ -3,16 +3,14 @@
 ; Don't assume that external global variables or those with weak linkage have
 ; their preferred alignment. They may only have the ABI minimum alignment.
 
-; CHECK: %s = shl i64 %a, 3
-; CHECK: %r = or i64 %s, ptrtoint (i32* @A to i64)
-; CHECK: %q = add i64 %r, 1
-; CHECK: ret i64 %q
-
 target datalayout = "i32:8:32"
 
 @A = external global i32
 @B = weak_odr global i32 0
 
+@C = available_externally global <4 x i32> zeroinitializer, align 4
+; CHECK: @C = available_externally global <4 x i32> zeroinitializer, align 4
+
 define i64 @foo(i64 %a) {
   %t = ptrtoint i32* @A to i64
   %s = shl i64 %a, 3
@@ -21,9 +19,23 @@ define i64 @foo(i64 %a) {
   ret i64 %q
 }
 
+; CHECK-LABEL: define i64 @foo(i64 %a)
+; CHECK: %s = shl i64 %a, 3
+; CHECK: %r = or i64 %s, ptrtoint (i32* @A to i64)
+; CHECK: %q = add i64 %r, 1
+; CHECK: ret i64 %q
+
 define i32 @bar() {
-; CHECK-LABEL: @bar(
   %r = load i32, i32* @B, align 1
-; CHECK: align 1
   ret i32 %r
 }
+
+; CHECK-LABEL: @bar()
+; CHECK: align 1
+
+define void @vec_store() {
+  store <4 x i32> <i32 0, i32 1, i32 2, i32 3>, <4 x i32>* @C, align 4
+  ret void
+}
+; CHECK: define void @vec_store()
+; CHECK: store <4 x i32> <i32 0, i32 1, i32 2, i32 3>, <4 x i32>* @C, align 4