[WebAssembly] Error when using wasm64 for ISel

[tlively]

Summary

64-bit WebAssembly (wasm64) is not specified and not supported in the
WebAssembly backend. We do have support for it in clang, however, and
we would like to keep that support because we expect wasm64 to be
specified and supported in the future. For now add an error when
trying to use wasm64 from the backend to minimize user confusion from
unexplained crashes.

[aheejin]

llvm/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp

60

How about 'not currently supported'? I don't want to make an impression that this is something that's meant not to be supported but also don't want to imply that we have plans to support that in the future, so... 🤷🏻‍♀️

llvm/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp

public:
 
   bool runOnMachineFunction(MachineFunction &MF) override {
     LLVM_DEBUG(dbgs() << "********** ISelDAGToDAG **********\n"
                          "********** Function: "
                       << MF.getName() << '\n');
 
     ForCodeSize = MF.getFunction().hasOptSize();
     Subtarget = &MF.getSubtarget<WebAssemblySubtarget>();
+
+    // Wasm64 is not fully supported right now (and is not specified)
+    if (Subtarget->hasAddr64())
+      report_fatal_error("64-bit WebAssembly (wasm64) is not supported");
+
     return SelectionDAGISel::runOnMachineFunction(MF);
   }
 
   void Select(SDNode *Node) override;
 
   bool SelectInlineAsmMemoryOperand(const SDValue &Op, unsigned ConstraintID,
                                     std::vector<SDValue> &OutOps) override;
 

llvm/test/CodeGen/WebAssembly/cpus.ll

 ; This tests that llc accepts all valid WebAssembly CPUs.
 
 ; RUN: llc < %s -asm-verbose=false -mtriple=wasm32-unknown-unknown -mcpu=mvp 2>&1 | FileCheck %s
-; RUN: llc < %s -asm-verbose=false -mtriple=wasm64-unknown-unknown-wasm -mcpu=mvp 2>&1 | FileCheck %s
+; RUN: not llc < %s -asm-verbose=false -mtriple=wasm64-unknown-unknown-wasm -mcpu=mvp 2>&1 | FileCheck %s --check-prefix=WASM64
 ; RUN: llc < %s -asm-verbose=false -mtriple=wasm32-unknown-unknown -mcpu=generic 2>&1 | FileCheck %s
-; RUN: llc < %s -asm-verbose=false -mtriple=wasm64-unknown-unknown-wasm -mcpu=generic 2>&1 | FileCheck %s
+; RUN: not llc < %s -asm-verbose=false -mtriple=wasm64-unknown-unknown-wasm -mcpu=generic 2>&1 | FileCheck %s  --check-prefix=WASM64
 ; RUN: llc < %s -asm-verbose=false -mtriple=wasm32-unknown-unknown -mcpu=bleeding-edge 2>&1 | FileCheck %s
-; RUN: llc < %s -asm-verbose=false -mtriple=wasm64-unknown-unknown-wasm -mcpu=bleeding-edge 2>&1 | FileCheck %s
+; RUN: not llc < %s -asm-verbose=false -mtriple=wasm64-unknown-unknown-wasm -mcpu=bleeding-edge 2>&1 | FileCheck %s  --check-prefix=WASM64
 ; RUN: llc < %s -asm-verbose=false -mtriple=wasm32-unknown-unknown -mcpu=invalidcpu 2>&1 | FileCheck %s --check-prefix=INVALID
-; RUN: llc < %s -asm-verbose=false -mtriple=wasm64-unknown-unknown-wasm -mcpu=invalidcpu 2>&1 | FileCheck %s --check-prefix=INVALID
+; RUN: not llc < %s -asm-verbose=false -mtriple=wasm64-unknown-unknown-wasm -mcpu=invalidcpu 2>&1 | FileCheck %s --check-prefix=WASM64
 
 ; CHECK-NOT: is not a recognized processor for this target
 ; INVALID: {{.+}} is not a recognized processor for this target
+; WASM64: 64-bit WebAssembly (wasm64) is not supported
 
 define i32 @f(i32 %i_like_the_web) {
   ret i32 %i_like_the_web
 }