Emit ABI_PCS_R9_use build attribute.

[bfoster]

Summary

Emit the build attribute describing how the r9 register is to be treated, (i.e. as V6 or not at all).

[bfoster]

Thanks for looking at this Saleem;

I've updated the enum name and added the remaining two as you suggested, and dropped a todo for properly passing this from the frontend.

[compnerd]

include/llvm/Support/ARMBuildAttributes.h

150

Aligning the comments would be nice.

[bfoster]

The comments are now aligned.

[rengolin]

LGTM, thanks!

[aemerson]

Closed by commit rL213944 (authored by @aemerson).

include/llvm/Support/ARMBuildAttributes.h

enum {
   AllowWMMXv1 = 1,  // The user permitted this entity to use WMMX v1
   AllowWMMXv2 = 2,  // The user permitted this entity to use WMMX v2
 
   // Tag_Advanced_SIMD_arch, (=12), uleb128
   AllowNeon = 1,      // SIMDv1 was permitted
   AllowNeon2 = 2,     // SIMDv2 was permitted (Half-precision FP, MAC operations)
   AllowNeonARMv8 = 3, // ARM v8-A SIMD was permitted
 
+  // Tag_ABI_PCS_R9_use, (=14), uleb128
+  R9UsedAsV6 = 0, // R9 used as v6 (just another callee-saved register)
+  R9Reserved = 3, // R9 not used at all by code associated with attributed entity
+
   // Tag_ABI_PCS_RW_data, (=15), uleb128
   AddressRWPCRel = 1, // Address RW static data PC-relative
   AddressRWSBRel = 2, // Address RW static data SB-relative
   AddressRWNone = 3, // No RW static data permitted
 
   // Tag_ABI_PCS_RO_data, (=14), uleb128
   AddressROPCRel = 1, // Address RO static data PC-relative
   AddressRONone = 2, // No RO static data permitted

lib/Target/ARM/ARMAsmPrinter.cpp

if (const Module *SourceModule = MMI->getModule()) {
         assert((EnumWidth == 1 || EnumWidth == 4) &&
                "Minimum enum width must be 1 or 4 bytes");
         int EnumBuildAttr = EnumWidth == 1 ? 1 : 2;
         ATS.emitAttribute(ARMBuildAttrs::ABI_enum_size, EnumBuildAttr);
       }
     }
   }
 
+  // ABI_PCS_R9_use, we only support either reserving the register, or treating
+  // it as another callee-saved register, but not as SB or a TLS pointer.
+  if (Subtarget->isR9Reserved())
+      ATS.emitAttribute(ARMBuildAttrs::ABI_PCS_R9_use,
+                        ARMBuildAttrs::R9Reserved);
+  else
+      ATS.emitAttribute(ARMBuildAttrs::ABI_PCS_R9_use,
+                        ARMBuildAttrs::R9UsedAsV6);
+
   if (Subtarget->hasTrustZone() && Subtarget->hasVirtualization())
       ATS.emitAttribute(ARMBuildAttrs::Virtualization_use,
                         ARMBuildAttrs::AllowTZVirtualization);
   else if (Subtarget->hasTrustZone())
       ATS.emitAttribute(ARMBuildAttrs::Virtualization_use,
                         ARMBuildAttrs::AllowTZ);
   else if (Subtarget->hasVirtualization())
       ATS.emitAttribute(ARMBuildAttrs::Virtualization_use,

test/CodeGen/ARM/build-attributes.ll

 ; RUN: llc < %s -mtriple=armv7-none-linux-gnueabi -mcpu=cortex-a7 -mattr=-vfp2,-vfp3,-vfp4,-neon | FileCheck %s --check-prefix=CORTEX-A7-NOFPU
 ; RUN: llc < %s -mtriple=armv7-none-linux-gnueabi -mcpu=cortex-a7 -mattr=+vfp4,-neon | FileCheck %s --check-prefix=CORTEX-A7-FPUV4
 ; RUN: llc < %s -mtriple=armv7-none-linux-gnueabi -mcpu=cortex-a7 -mattr=+vfp4,,+d16,-neon | FileCheck %s --check-prefix=CORTEX-A7-FPUV4
 ; RUN: llc < %s -mtriple=arm-none-linux-gnueabi -relocation-model=pic | FileCheck %s --check-prefix=RELOC-PIC
 ; RUN: llc < %s -mtriple=arm-none-linux-gnueabi -relocation-model=static | FileCheck %s --check-prefix=RELOC-OTHER
 ; RUN: llc < %s -mtriple=arm-none-linux-gnueabi -relocation-model=default | FileCheck %s --check-prefix=RELOC-OTHER
 ; RUN: llc < %s -mtriple=arm-none-linux-gnueabi -relocation-model=dynamic-no-pic | FileCheck %s --check-prefix=RELOC-OTHER
 ; RUN: llc < %s -mtriple=arm-none-linux-gnueabi | FileCheck %s --check-prefix=RELOC-OTHER
+; RUN: llc < %s -mtriple=arm-none-linux-gnueabi | FileCheck %s --check-prefix=PCS-R9-USE
+; RUN: llc < %s -mtriple=arm-none-linux-gnueabi -arm-reserve-r9 | FileCheck %s --check-prefix=PCS-R9-RESERVE
 
 ; XSCALE:      .eabi_attribute 6, 5
 ; XSCALE:      .eabi_attribute 8, 1
 ; XSCALE:      .eabi_attribute 9, 1
 
 ; V6:   .eabi_attribute 6, 6
 ; V6:   .eabi_attribute 8, 1
 ; V6:   .eabi_attribute 24, 1

 ; CORTEX-A57-NOT:  .eabi_attribute 44
 ; CORTEX-A57:  .eabi_attribute 68, 3
 
 ; RELOC-PIC:  .eabi_attribute 15, 1
 ; RELOC-PIC:  .eabi_attribute 16, 1
 ; RELOC-PIC:  .eabi_attribute 17, 2
 ; RELOC-OTHER:  .eabi_attribute 17, 1
 
+; PCS-R9-USE:  .eabi_attribute 14, 0
+; PCS-R9-RESERVE:  .eabi_attribute 14, 3
+
 define i32 @f(i64 %z) {
   ret i32 0
 }