[WebAssembly] Made disassembler only use stack instructions.

Summary:
Now uses the StackBased bit from the tablegen defs to identify
stack instructions (and ignore register based or non-wasm instructions).

Also changed how we store operands, since we now have up to 16 of them
per instruction. To not cause static data bloat, these are compressed
into a tiny table.

+ a few other cleanups.

Tested:
- MCTest
- llvm-lit -v `find test -name WebAssembly`

Reviewers: dschuff, jgravelle-google, sunfish, tlively

Subscribers: sbc100, aheejin, llvm-commits

Differential Revision: https://reviews.llvm.org/D51320

llvm-svn: 341081

1 files changed, 7 insertions, 10 deletions

diff --git a/llvm/lib/Target/WebAssembly/Disassembler/WebAssemblyDisassembler.cpp b/llvm/lib/Target/WebAssembly/Disassembler/WebAssemblyDisassembler.cpp
index 9f6797d..896a722 100644
--- a/llvm/lib/Target/WebAssembly/Disassembler/WebAssemblyDisassembler.cpp
+++ b/llvm/lib/Target/WebAssembly/Disassembler/WebAssemblyDisassembler.cpp
@@ -140,7 +140,7 @@ MCDisassembler::DecodeStatus WebAssemblyDisassembler::getInstruction(
   MI.setOpcode(WasmInst->Opcode);
   // Parse any operands.
   for (uint8_t OPI = 0; OPI < WasmInst->NumOperands; OPI++) {
-    switch (WasmInst->Operands[OPI]) {
+    switch (OperandTable[WasmInst->OperandStart + OPI]) {
     // ULEB operands:
     case WebAssembly::OPERAND_BASIC_BLOCK:
     case WebAssembly::OPERAND_LOCAL:
@@ -194,15 +194,12 @@ MCDisassembler::DecodeStatus WebAssemblyDisassembler::getInstruction(
         return MCDisassembler::Fail;
       break;
     }
-    case MCOI::OPERAND_REGISTER: {
-      // These are NOT actually in the instruction stream, but MC is going to
-      // expect operands to be present for them!
-      // FIXME: can MC re-generate register assignments or do we have to
-      // do this? Since this function decodes a single instruction, we don't
-      // have the proper context for tracking an operand stack here.
-      MI.addOperand(MCOperand::createReg(0));
-      break;
-    }
+    case MCOI::OPERAND_REGISTER:
+      // The tablegen header currently does not have any register operands since
+      // we use only the stack (_S) instructions.
+      // If you hit this that probably means a bad instruction definition in
+      // tablegen.
+      llvm_unreachable("Register operand in WebAssemblyDisassembler");
     default:
       llvm_unreachable("Unknown operand type in WebAssemblyDisassembler");
     }