[AMDGPU] Add default ISA version targets

[rampitec]

Summary

In case if -mattr used to modify feature set bits in llvm-mc call
getIsaVersion can fail to identify specific ISA due to test mismatch.
Adding default fallback tests which will always correctly report at
least major version.

[kzhuravl]

LGTM.

[artem.tamazov]

It seems that -mattr corrupts the design. What is the purpose of this option?

llvm/trunk/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp

IsaVersion getIsaVersion(const FeatureBitset &Features) {
   if (Features.test(FeatureISAVersion7_0_1))
     return {7, 0, 1};
   if (Features.test(FeatureISAVersion7_0_2))
     return {7, 0, 2};
   if (Features.test(FeatureISAVersion7_0_3))
     return {7, 0, 3};
   if (Features.test(FeatureISAVersion7_0_4))
     return {7, 0, 4};
+  if (Features.test(FeatureSeaIslands))
+    return {7, 0, 0};
 
   // GCN GFX8 (Volcanic Islands (VI)).
   if (Features.test(FeatureISAVersion8_0_1))
     return {8, 0, 1};
   if (Features.test(FeatureISAVersion8_0_2))
     return {8, 0, 2};
   if (Features.test(FeatureISAVersion8_0_3))
     return {8, 0, 3};
   if (Features.test(FeatureISAVersion8_1_0))
     return {8, 1, 0};
+  if (Features.test(FeatureVolcanicIslands))
+    return {8, 0, 0};
 
   // GCN GFX9.
   if (Features.test(FeatureISAVersion9_0_0))
     return {9, 0, 0};
   if (Features.test(FeatureISAVersion9_0_2))
     return {9, 0, 2};
+  if (Features.test(FeatureGFX9))
+    return {9, 0, 0};
 
   if (!Features.test(FeatureGCN) || Features.test(FeatureSouthernIslands))
     return {0, 0, 0};
   return {7, 0, 0};
 }
 
 void streamIsaVersion(const MCSubtargetInfo *STI, raw_ostream &Stream) {
   auto TargetTriple = STI->getTargetTriple();

llvm/trunk/test/MC/AMDGPU/hsa_isa_version_attrs.s

+// RUN: llvm-mc -arch=amdgcn -mcpu=gfx801 -mattr=-fast-fmaf -show-encoding %s | FileCheck --check-prefix=GFX8 %s
+// RUN: llvm-mc -arch=amdgcn -mcpu=gfx900 -mattr=-mad-mix-insts -show-encoding %s | FileCheck --check-prefix=GFX9 %s
+
+.hsa_code_object_isa
+// GFX8:  .hsa_code_object_isa 8,0,0,"AMD","AMDGPU"
+// GFX9:  .hsa_code_object_isa 9,0,0,"AMD","AMDGPU"