WebAssembly: add a generic CPU

[jfb]

Summary

WebAssemblySubtarget.cpp expects a default 'generic' CPU to exist, and this seems to be prevalent with other targets. It makes sense to have something between MVP and bleeding-edge, even though for now it's the same as MVP. This removes a warning that's currently generated.

lib/Target/WebAssembly/WebAssembly.td

 
 //===----------------------------------------------------------------------===//
 // WebAssembly Processors supported.
 //===----------------------------------------------------------------------===//
 
 // Minimal Viable Product.
 def : ProcessorModel<"mvp", NoSchedModel, []>;
 
+// Generic processor: latest stable version.
+def : ProcessorModel<"generic", NoSchedModel, []>;
+
 // Latest and greatest experimental version of WebAssembly. Bugs included!
 def : ProcessorModel<"bleeding-edge", NoSchedModel, [FeatureSIMD128]>;
 
 //===----------------------------------------------------------------------===//
 // Target Declaration
 //===----------------------------------------------------------------------===//
 
 def WebAssembly : Target {
   let InstructionSet = WebAssemblyInstrInfo;
 }

test/CodeGen/WebAssembly/cpus.ll

 ; This tests that llc accepts all valid WebAssembly CPUs.
 
 ; RUN: llc < %s -mtriple=wasm32-unknown-unknown -mcpu=mvp 2>&1 | FileCheck %s
 ; RUN: llc < %s -mtriple=wasm64-unknown-unknown -mcpu=mvp 2>&1 | FileCheck %s
+; RUN: llc < %s -mtriple=wasm32-unknown-unknown -mcpu=generic 2>&1 | FileCheck %s
+; RUN: llc < %s -mtriple=wasm64-unknown-unknown -mcpu=generic 2>&1 | FileCheck %s
 ; RUN: llc < %s -mtriple=wasm32-unknown-unknown -mcpu=bleeding-edge 2>&1 | FileCheck %s
 ; RUN: llc < %s -mtriple=wasm64-unknown-unknown -mcpu=bleeding-edge 2>&1 | FileCheck %s
 ; RUN: llc < %s -mtriple=wasm32-unknown-unknown -mcpu=invalidcpu 2>&1 | FileCheck %s --check-prefix=INVALID
 ; RUN: llc < %s -mtriple=wasm64-unknown-unknown -mcpu=invalidcpu 2>&1 | FileCheck %s --check-prefix=INVALID
 
 ; CHECK-NOT: {{.*}}  is not a recognized processor for this target
 ; INVALID: {{.*}}  is not a recognized processor for this target
 
 define void @f(i64 %i_like_the_web) {
   ret void
 }