From b033aba61bf05719c8481a38c06d88c3805b45a9 Mon Sep 17 00:00:00 2001
From: Trevor Elliott <telliott@fastly.com>
Date: Tue, 30 Aug 2022 09:14:20 -0700
Subject: [PATCH] Move the nop lowering to ISLE, and remove the final return
 from lower.rs (#4809)

Lower nop in ISLE in the x64 backend, and remove the final Ok(()) from the lower function to assert that all cases that aren't handled in ISLE will panic.
---
 cranelift/codegen/src/isa/x64/lower.isle | 6 ++++++
 cranelift/codegen/src/isa/x64/lower.rs   | 9 ++-------
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/cranelift/codegen/src/isa/x64/lower.isle b/cranelift/codegen/src/isa/x64/lower.isle
index 23f18a73f0..b86c2fe792 100644
--- a/cranelift/codegen/src/isa/x64/lower.isle
+++ b/cranelift/codegen/src/isa/x64/lower.isle
@@ -3758,3 +3758,9 @@
 
         ;; SHUFPS xmm_y, xmm_xmp, 0x88
         (x64_shufps dst zeros 0x88)))
+
+;; Rules for `nop` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(rule (lower (nop))
+      (invalid_reg))
+
diff --git a/cranelift/codegen/src/isa/x64/lower.rs b/cranelift/codegen/src/isa/x64/lower.rs
index 6d1a0bec61..88ef7e500c 100644
--- a/cranelift/codegen/src/isa/x64/lower.rs
+++ b/cranelift/codegen/src/isa/x64/lower.rs
@@ -459,7 +459,8 @@ fn lower_insn_to_regs(
         | Opcode::Isplit
         | Opcode::TlsValue
         | Opcode::SqmulRoundSat
-        | Opcode::Uunarrow => {
+        | Opcode::Uunarrow
+        | Opcode::Nop => {
             let ty = if outputs.len() > 0 {
                 Some(ctx.output_ty(insn, 0))
             } else {
@@ -572,13 +573,7 @@ fn lower_insn_to_regs(
         | Opcode::BrTable => {
             panic!("Branch opcode reached non-branch lowering logic!");
         }
-
-        Opcode::Nop => {
-            // Nothing.
-        }
     }
-
-    Ok(())
 }
 
 //=============================================================================