[AMDGPU] Corrected directive to use for ELF weak refs

[dp]

Summary

WeakRefDirective should specify a directive to declare "a global as being a weak undefined symbol".

The directive used by AMDGPU is incorrect - ".weakref" is intended for other purposes.
The correct directive is ".weak" and it is already defined as default for ELF.

This issue was found when compiling a HIP program using -O0 -save-temps. The following declaration

%struct.__hip_builtin_blockIdx_t = type { i8 }
@blockIdx = extern_weak dso_local protected addrspace(1) global %struct.__hip_builtin_blockIdx_t, align 1

resulted in code which cannot be assembled:

.protected	blockIdx
.weakref	blockIdx

[arsenm]

Needs test

[dp]

Added a test

llvm/lib/Target/AMDGPU/MCTargetDesc/AMDGPUMCAsmInfo.cpp

AMDGPUMCAsmInfo::AMDGPUMCAsmInfo(const Triple &TT,
   //===--- Data Emission Directives -------------------------------------===//
   SunStyleELFSectionSwitchSyntax = true;
   UsesELFSectionDirectiveForBSS = true;
 
   //===--- Global Variable Emission Directives --------------------------===//
   HasAggressiveSymbolFolding = true;
   COMMDirectiveAlignmentIsInBytes = false;
   HasNoDeadStrip = true;
-  WeakRefDirective = ".weakref\t";
   //===--- Dwarf Emission Directives -----------------------------------===//
   SupportsDebugInformation = true;
   DwarfRegNumForCFI = true;
 
   UseIntegratedAssembler = false;
 }
 
 bool AMDGPUMCAsmInfo::shouldOmitSectionDirective(StringRef SectionName) const {

llvm/test/CodeGen/AMDGPU/hsa-globals.ll

 ; RUN: llc < %s -mtriple=amdgcn--amdhsa -mcpu=kaveri | FileCheck --check-prefix=ASM %s
 
 @linkonce_odr_global_program = linkonce_odr addrspace(1) global i32 0
 @linkonce_global_program = linkonce addrspace(1) global i32 0
 @internal_global_program = internal addrspace(1) global i32 0
 @common_global_program = common addrspace(1) global i32 0
 @external_global_program = addrspace(1) global i32 0
 
 @internal_readonly = internal unnamed_addr addrspace(4) constant i32 0
 @external_readonly = unnamed_addr addrspace(4) constant i32 0
 
 define amdgpu_kernel void @test() {
   ret void
 }
 
+@weak_global = extern_weak addrspace(1) global i32
+
 ; ASM: .type linkonce_odr_global_program,@object
 ; ASM: .section .bss,#alloc,#write
 ; ASM: .weak linkonce_odr_global_program
 ; ASM: linkonce_odr_global_program:
 ; ASM: .long 0
 ; ASM: .size linkonce_odr_global_program, 4
 
 ; ASM: .type linkonce_global_program,@object

 ; ASM: .long 0
 ; ASM: .size internal_readonly, 4
 
 ; ASM: .type external_readonly,@object
 ; ASM: .globl external_readonly
 ; ASM: external_readonly:
 ; ASM: .long 0
 ; ASM: .size external_readonly, 4
+
+; ASM: .weak weak_global