Support the assume_aligned function attribute

In addition to __builtin_assume_aligned, GCC also supports an assume_aligned
attribute which specifies the alignment (and optional offset) of a function's
return value. Here we implement support for the assume_aligned attribute by making
use of the @llvm.assume intrinsic.

llvm-svn: 218500

1 files changed, 29 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 62a3e11ac9a..9d194a3ad14 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -129,6 +129,29 @@ static void instantiateDependentAlignedAttr(
   }
 }
 
+static void instantiateDependentAssumeAlignedAttr(
+    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
+    const AssumeAlignedAttr *Aligned, Decl *New) {
+  // The alignment expression is a constant expression.
+  EnterExpressionEvaluationContext Unevaluated(S, Sema::ConstantEvaluated);
+
+  Expr *E, *OE = nullptr;
+  ExprResult Result = S.SubstExpr(Aligned->getAlignment(), TemplateArgs);
+  if (Result.isInvalid())
+    return;
+  E = Result.getAs<Expr>();
+
+  if (Aligned->getOffset()) {
+    Result = S.SubstExpr(Aligned->getOffset(), TemplateArgs);
+    if (Result.isInvalid())
+      return;
+    OE = Result.getAs<Expr>();
+  }
+
+  S.AddAssumeAlignedAttr(Aligned->getLocation(), New, E, OE,
+                         Aligned->getSpellingListIndex());
+}
+
 static void instantiateDependentEnableIfAttr(
     Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
     const EnableIfAttr *A, const Decl *Tmpl, Decl *New) {
@@ -176,6 +199,12 @@ void Sema::InstantiateAttrs(const MultiLevelTemplateArgumentList &TemplateArgs,
       continue;
     }
 
+    const AssumeAlignedAttr *AssumeAligned = dyn_cast<AssumeAlignedAttr>(TmplAttr);
+    if (AssumeAligned) {
+      instantiateDependentAssumeAlignedAttr(*this, TemplateArgs, AssumeAligned, New);
+      continue;
+    }
+
     const EnableIfAttr *EnableIf = dyn_cast<EnableIfAttr>(TmplAttr);
     if (EnableIf && EnableIf->getCond()->isValueDependent()) {
       instantiateDependentEnableIfAttr(*this, TemplateArgs, EnableIf, Tmpl,