[AMDGPU] Add default ISA version targets

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.

Differential Revision: https://reviews.llvm.org/D44163

llvm-svn: 326825
diff --git a/llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp b/llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp
index 7848a29..69572b8 100644
--- a/llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp
@@ -206,6 +206,8 @@
     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))
@@ -216,12 +218,16 @@
     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};