[WebAssembly] Make disassembler always emit most canonical name.

Summary:
There are a few instructions that all map to the same opcode, so
when disassembling, we have to pick one. That was just the first one
before (the except_ref variant in the case of "call"), now it is the
one marked as IsCanonical in tablegen, or failing that, the shortest
name (which is typically the "canonical" one).

Also introduced a canonical "end" instruction for this purpose.

Reviewers: dschuff, tlively

Subscribers: sbc100, jgravelle-google, aheejin, llvm-commits, sunfish

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D57713

llvm-svn: 353131

1 files changed, 3 insertions, 0 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyInstrFormats.td b/llvm/lib/Target/WebAssembly/WebAssemblyInstrFormats.td
index 2a2c79c56d6..aff4d20d8d8 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyInstrFormats.td
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyInstrFormats.td
@@ -22,6 +22,9 @@ class WebAssemblyInst<bits<32> inst, string asmstr, string stack> : StackRel,
   let Namespace   = "WebAssembly";
   let Pattern     = [];
   let AsmString   = asmstr;
+  // When there are multiple instructions that map to the same encoding (in
+  // e.g. the disassembler use case) prefer the one where IsCanonical == 1.
+  bit IsCanonical = 0;
 }
 
 // Normal instructions. Default instantiation of a WebAssemblyInst.