From 7651dd8359c70035ee12a3bafdb25062bb3e90a2 Mon Sep 17 00:00:00 2001
From: Akira Hatanaka <ahatanaka@apple.com>
Date: Tue, 28 Jul 2015 22:26:45 +0000
Subject: [PATCH] [ARM] Pass subtarget feature "+strict-align".

This commit changes the driver to save subtarget feature "+strict-align" to the
IR instead of using backend option "arm-strict-align". This is needed for LTO.

Also, move the logic in ARM backend that was deciding whether strict alignment
should be forced to the front-end.

rdar://problem/21529937

http://reviews.llvm.org/D11472

llvm-svn: 243489
---
 clang/lib/Driver/Tools.cpp             | 57 +++++++++++++++++++++-------------
 clang/test/Driver/apple-kext-mkernel.c |  4 +--
 clang/test/Driver/arm-alignment.c      | 31 ++++++++++++++++--
 3 files changed, 67 insertions(+), 25 deletions(-)

diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index f5cb90e..f554cae 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -799,6 +799,42 @@ static void getARMTargetFeatures(const Driver &D, const llvm::Triple &Triple,
       Features.push_back("+long-calls");
   }
 
+  // Kernel code has more strict alignment requirements.
+  if (KernelOrKext)
+    Features.push_back("+strict-align");
+  else if (Arg *A = Args.getLastArg(options::OPT_mno_unaligned_access,
+                                    options::OPT_munaligned_access)) {
+    if (A->getOption().matches(options::OPT_munaligned_access)) {
+      // No v6M core supports unaligned memory access (v6M ARM ARM A3.2).
+      if (Triple.getSubArch() == llvm::Triple::SubArchType::ARMSubArch_v6m)
+        D.Diag(diag::err_target_unsupported_unaligned) << "v6m";
+    } else
+      Features.push_back("+strict-align");
+  } else {
+    // Assume pre-ARMv6 doesn't support unaligned accesses.
+    //
+    // ARMv6 may or may not support unaligned accesses depending on the
+    // SCTLR.U bit, which is architecture-specific. We assume ARMv6
+    // Darwin and NetBSD targets support unaligned accesses, and others don't.
+    //
+    // ARMv7 always has SCTLR.U set to 1, but it has a new SCTLR.A bit
+    // which raises an alignment fault on unaligned accesses. Linux
+    // defaults this bit to 0 and handles it as a system-wide (not
+    // per-process) setting. It is therefore safe to assume that ARMv7+
+    // Linux targets support unaligned accesses. The same goes for NaCl.
+    //
+    // The above behavior is consistent with GCC.
+    int VersionNum = getARMSubArchVersionNumber(Triple);
+    if (Triple.isOSDarwin() || Triple.isOSNetBSD()) {
+      if (VersionNum < 6)
+        Features.push_back("+strict-align");
+    } else if (Triple.isOSLinux() || Triple.isOSNaCl()) {
+      if (VersionNum < 7)
+        Features.push_back("+strict-align");
+    } else
+      Features.push_back("+strict-align");
+  }
+
   // llvm does not support reserving registers in general. There is support
   // for reserving r9 on ARM though (defined as a platform-specific register
   // in ARM EABI).
@@ -879,27 +915,6 @@ void Clang::AddARMTargetArgs(const ArgList &Args, ArgStringList &CmdArgs,
     CmdArgs.push_back("hard");
   }
 
-  // Kernel code has more strict alignment requirements.
-  if (KernelOrKext) {
-    CmdArgs.push_back("-backend-option");
-    CmdArgs.push_back("-arm-strict-align");
-  }
-
-  // -mkernel implies -mstrict-align; don't add the redundant option.
-  if (!KernelOrKext) {
-    if (Arg *A = Args.getLastArg(options::OPT_mno_unaligned_access,
-                                 options::OPT_munaligned_access)) {
-      CmdArgs.push_back("-backend-option");
-      if (A->getOption().matches(options::OPT_mno_unaligned_access))
-        CmdArgs.push_back("-arm-strict-align");
-      else {
-        if (Triple.getSubArch() == llvm::Triple::SubArchType::ARMSubArch_v6m)
-          D.Diag(diag::err_target_unsupported_unaligned) << "v6m";
-        CmdArgs.push_back("-arm-no-strict-align");
-      }
-    }
-  }
-
   // Forward the -mglobal-merge option for explicit control over the pass.
   if (Arg *A = Args.getLastArg(options::OPT_mglobal_merge,
                                options::OPT_mno_global_merge)) {
diff --git a/clang/test/Driver/apple-kext-mkernel.c b/clang/test/Driver/apple-kext-mkernel.c
index 5f4f522..9c20cfc 100644
--- a/clang/test/Driver/apple-kext-mkernel.c
+++ b/clang/test/Driver/apple-kext-mkernel.c
@@ -12,8 +12,8 @@
 // RUN: FileCheck --check-prefix=CHECK-ARM < %t %s
 
 // CHECK-ARM: "-target-feature" "+long-calls"
-// CHECK-ARM: "-backend-option" "-arm-strict-align"
-// CHECK-ARM-NOT: "-backend-option" "-arm-strict-align"
+// CHECK-ARM: "-target-feature" "+strict-align"
+// CHECK-ARM-NOT: "-target-feature" "+strict-align"
 // CHECK-ARM: "-fno-builtin"
 // CHECK-ARM: "-fno-rtti"
 // CHECK-ARM: "-fno-common"
diff --git a/clang/test/Driver/arm-alignment.c b/clang/test/Driver/arm-alignment.c
index 3fe5951..21caf83 100644
--- a/clang/test/Driver/arm-alignment.c
+++ b/clang/test/Driver/arm-alignment.c
@@ -7,6 +7,18 @@
 // RUN: %clang -target arm-none-gnueabi -mno-unaligned-access -munaligned-access -### %s 2> %t
 // RUN: FileCheck --check-prefix=CHECK-UNALIGNED-ARM < %t %s
 
+// RUN: %clang -target armv6-apple-darwin -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-UNALIGNED-ARM < %t %s
+
+// RUN: %clang -target armv6-netbsd-eabi -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-UNALIGNED-ARM < %t %s
+
+// RUN: %clang -target armv7-unknown-linux -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-UNALIGNED-ARM < %t %s
+
+// RUN: %clang -target armv7-unknown-nacl-gnueabihf -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-UNALIGNED-ARM < %t %s
+
 // RUN: %clang -target aarch64-none-gnueabi -munaligned-access -### %s 2> %t
 // RUN: FileCheck --check-prefix=CHECK-UNALIGNED-AARCH64 < %t %s
 
@@ -16,7 +28,7 @@
 // RUN: %clang -target aarch64-none-gnueabi -mno-unaligned-access -munaligned-access -### %s 2> %t
 // RUN: FileCheck --check-prefix=CHECK-UNALIGNED-AARCH64 < %t %s
 
-// CHECK-UNALIGNED-ARM: "-backend-option" "-arm-no-strict-align"
+// CHECK-UNALIGNED-ARM-NOT: "-target-feature" "+strict-align"
 // CHECK-UNALIGNED-AARCH64: "-backend-option" "-aarch64-no-strict-align"
 
 
@@ -32,6 +44,21 @@
 // RUN: %clang -target arm-none-gnueabi -munaligned-access -mstrict-align -### %s 2> %t
 // RUN: FileCheck --check-prefix=CHECK-ALIGNED-ARM < %t %s
 
+// RUN: %clang -target arm-none-gnueabi -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-ALIGNED-ARM < %t %s
+
+// RUN: %clang -target armv5-apple-darwin -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-ALIGNED-ARM < %t %s
+
+// RUN: %clang -target armv5t-netbsd-eabi -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-ALIGNED-ARM < %t %s
+
+// RUN: %clang -target armv6-unknown-linux -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-ALIGNED-ARM < %t %s
+
+// RUN: %clang -target armv6-unknown-nacl-gnueabihf -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-ALIGNED-ARM < %t %s
+
 // RUN: %clang -target aarch64-none-gnueabi -mno-unaligned-access -### %s 2> %t
 // RUN: FileCheck --check-prefix=CHECK-ALIGNED-AARCH64 < %t %s
 
@@ -47,7 +74,7 @@
 // RUN: %clang -target aarch64-none-gnueabi -mkernel -mno-unaligned-access -### %s 2> %t
 // RUN: FileCheck --check-prefix=CHECK-ALIGNED-AARCH64 < %t %s
 
-// CHECK-ALIGNED-ARM: "-backend-option" "-arm-strict-align"
+// CHECK-ALIGNED-ARM: "-target-feature" "+strict-align"
 // CHECK-ALIGNED-AARCH64: "-backend-option" "-aarch64-strict-align"
 
 // Make sure that v6M cores always trigger the unsupported aligned accesses error
-- 
2.7.4