Introduce f[no-]max-unknown-pointer-align=[number] option

to instruct the code generator to not enforce a higher alignment 
than the given number (of bytes) when accessing memory via an opaque 
pointer or reference. Patch reviewed by John McCall (with post-commit
review pending). rdar://16254558

llvm-svn: 214911

3 files changed, 22 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index 84962927990..a200548aa0e 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -1399,8 +1399,13 @@ public:
 
   LValue MakeNaturalAlignAddrLValue(llvm::Value *V, QualType T) {
     CharUnits Alignment;
-    if (!T->isIncompleteType())
+    if (!T->isIncompleteType()) {
       Alignment = getContext().getTypeAlignInChars(T);
+      unsigned MaxAlign = getContext().getLangOpts().MaxTypeAlign;
+      if (MaxAlign && Alignment.getQuantity() > MaxAlign &&
+          !getContext().isAlignmentRequired(T))
+        Alignment = CharUnits::fromQuantity(MaxAlign);
+    }
     return LValue::MakeAddr(V, T, Alignment, getContext(),
                             CGM.getTBAAInfo(T));
   }
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 9a205b3f5f4..93a1d914a0c 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -4134,6 +4134,21 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back("-fpack-struct=1");
   }
 
+  // Handle -fmax-type-align=N and -fno-type-align
+  bool SkipMaxTypeAlign = Args.hasArg(options::OPT_fno_max_type_align);
+  if (Arg *A = Args.getLastArg(options::OPT_fmax_type_align_EQ)) {
+    if (!SkipMaxTypeAlign) {
+      std::string MaxTypeAlignStr = "-fmax-type-align=";
+      MaxTypeAlignStr += A->getValue();
+      CmdArgs.push_back(Args.MakeArgString(MaxTypeAlignStr));
+    }
+  } else if (getToolChain().getTriple().isOSDarwin()) {
+    if (!SkipMaxTypeAlign) {
+      std::string MaxTypeAlignStr = "-fmax-type-align=16";
+      CmdArgs.push_back(Args.MakeArgString(MaxTypeAlignStr));
+    }
+  }
+
   if (KernelOrKext || isNoCommonDefault(getToolChain().getTriple())) {
     if (!Args.hasArg(options::OPT_fcommon))
       CmdArgs.push_back("-fno-common");
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 0fbbf1aa2fa..e4be487d7d6 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1476,6 +1476,7 @@ static void ParseLangArgs(LangOptions &Opts, ArgList &Args, InputKind IK,
     Args.hasArg(OPT_fencode_extended_block_signature);
   Opts.EmitAllDecls = Args.hasArg(OPT_femit_all_decls);
   Opts.PackStruct = getLastArgIntValue(Args, OPT_fpack_struct_EQ, 0, Diags);
+  Opts.MaxTypeAlign = getLastArgIntValue(Args, OPT_fmax_type_align_EQ, 0, Diags);
   Opts.PICLevel = getLastArgIntValue(Args, OPT_pic_level, 0, Diags);
   Opts.PIELevel = getLastArgIntValue(Args, OPT_pie_level, 0, Diags);
   Opts.Static = Args.hasArg(OPT_static_define);