[ARM] Pass subtarget feature "+strict-align" instead of backend option "arm-strict-align"

[ahatanak]

Summary

This is change is needed for LTO since anything passed via backend-option does not make it to the backend.

The corresponding llvm patch is here: http://reviews.llvm.org/D11470

[jfb]

test/Driver/arm-alignment.c

20

aarch64 also has its own option? Should your patch (or a follow-up) fix both?

[ahatanak]

Yes, fixing aarch64's strict-align was going to be my next patch.

[jfb]

In D11472#210943, @ahatanak wrote:

Yes, fixing aarch64's strict-align was going to be my next patch.

I think you may want to do it in this patch: you're generalizing something ARM does, but only using the new generalism in ARM. Having 2 targets use it would make this better IMO :-)

[ahatanak]

Added test cases for clang driver.

[jfb]

This lgtm, considering the comments on D11470.

Please do follow-up with equivalent aarch64 changes!

[Eugene.Zelenko]

Committed in rL243489.

lib/Driver/Tools.cpp

static void getARMTargetFeatures(const Driver &D, const llvm::Triple &Triple,
   if (Arg *A = Args.getLastArg(options::OPT_mlong_calls,
                                options::OPT_mno_long_calls)) {
     if (A->getOption().matches(options::OPT_mlong_calls))
       Features.push_back("+long-calls");
   } else if (KernelOrKext && (!Triple.isiOS() || Triple.isOSVersionLT(6))) {
       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).
   if (Args.hasArg(options::OPT_ffixed_r9))
     Features.push_back("+reserve-r9");
 
   // The kext linker doesn't know how to deal with movw/movt.
   if (KernelOrKext)
if (FloatABI == "soft") {
     CmdArgs.push_back("soft");
   } else {
     // Floating point operations and argument passing are hard.
     assert(FloatABI == "hard" && "Invalid float abi!");
     CmdArgs.push_back("-mfloat-abi");
     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)) {
     CmdArgs.push_back("-backend-option");
     if (A->getOption().matches(options::OPT_mno_global_merge))
       CmdArgs.push_back("-arm-global-merge=false");
     else
       CmdArgs.push_back("-arm-global-merge=true");

test/Driver/apple-kext-mkernel.c

 // RUN: %clang -target x86_64-apple-darwin10 \
 // RUN:   -mkernel -### -fsyntax-only %s 2> %t
 // RUN: FileCheck --check-prefix=CHECK-X86 < %t %s
 
 // CHECK-X86: "-disable-red-zone"
 // CHECK-X86: "-fno-builtin"
 // CHECK-X86: "-fno-rtti"
 // CHECK-X86: "-fno-common"
 
 // RUN: %clang -target x86_64-apple-darwin10 \
 // RUN:   -arch armv7 -mkernel -mstrict-align -### -fsyntax-only %s 2> %t
 // 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"
 
 // RUN: %clang -target x86_64-apple-darwin10 \
 // RUN:   -Werror -fno-builtin -fno-exceptions -fno-common -fno-rtti \
 // RUN:   -mkernel -fsyntax-only %s

test/Driver/arm-alignment.c

 // RUN: FileCheck --check-prefix=CHECK-UNALIGNED-AARCH64 < %t %s
 
 // RUN: %clang -target aarch64-none-gnueabi -mstrict-align -munaligned-access -### %s 2> %t
 // RUN: FileCheck --check-prefix=CHECK-UNALIGNED-AARCH64 < %t %s
 
 // 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"
 
 
 // RUN: %clang -target arm-none-gnueabi -mno-unaligned-access -### %s 2> %t
 // RUN: FileCheck --check-prefix=CHECK-ALIGNED-ARM < %t %s
 
 // RUN: %clang -target arm-none-gnueabi -mstrict-align -### %s 2> %t
 // RUN: FileCheck --check-prefix=CHECK-ALIGNED-ARM < %t %s
 

 // RUN: FileCheck --check-prefix=CHECK-ALIGNED-AARCH64 < %t %s
 
 // RUN: %clang -target aarch64-none-gnueabi -munaligned-access -mstrict-align -### %s 2> %t
 // RUN: FileCheck --check-prefix=CHECK-ALIGNED-AARCH64 < %t %s
 
 // 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
 // for all supported architecture triples.
 // RUN: not %clang -c -target thumbv6m-none-gnueabi -mcpu=cortex-m0 -munaligned-access %s 2>&1 | \
 // RUN:   FileCheck --check-prefix CHECK-UNALIGN-NOT-SUPPORTED %s
 // RUN: not %clang -c -target thumb-none-gnueabi -mcpu=cortex-m0 -munaligned-access %s 2>&1 | \
 // RUN:   FileCheck --check-prefix CHECK-UNALIGN-NOT-SUPPORTED %s
 
 // CHECK-UNALIGN-NOT-SUPPORTED: error: the v6m sub-architecture does not support unaligned accesses