From 74261ccd791e7f83382ca8b77149c7704c6d9cca Mon Sep 17 00:00:00 2001
From: bjorn3 <bjorn3@users.noreply.github.com>
Date: Sun, 31 Oct 2021 18:47:13 +0100
Subject: [PATCH] Never use the first vararg as typevar operand

If an instruction only takes varargs as values, it may have no arguments
at all.
---
 cranelift/codegen/meta/src/cdsl/formats.rs |  4 +--
 cranelift/codegen/meta/src/gen_inst.rs     | 30 ++++++++++------------
 2 files changed, 16 insertions(+), 18 deletions(-)

diff --git a/cranelift/codegen/meta/src/cdsl/formats.rs b/cranelift/codegen/meta/src/cdsl/formats.rs
index d445a4ed7e..6cd20ecae6 100644
--- a/cranelift/codegen/meta/src/cdsl/formats.rs
+++ b/cranelift/codegen/meta/src/cdsl/formats.rs
@@ -133,7 +133,7 @@ impl InstructionFormatBuilder {
 
     pub fn typevar_operand(mut self, operand_index: usize) -> Self {
         assert!(self.typevar_operand.is_none());
-        assert!(self.has_value_list || operand_index < self.num_value_operands);
+        assert!(operand_index < self.num_value_operands);
         self.typevar_operand = Some(operand_index);
         self
     }
@@ -141,7 +141,7 @@ impl InstructionFormatBuilder {
     pub fn build(self) -> Rc<InstructionFormat> {
         let typevar_operand = if self.typevar_operand.is_some() {
             self.typevar_operand
-        } else if self.has_value_list || self.num_value_operands > 0 {
+        } else if self.num_value_operands > 0 {
             // Default to the first value operand, if there's one.
             Some(0)
         } else {
diff --git a/cranelift/codegen/meta/src/gen_inst.rs b/cranelift/codegen/meta/src/gen_inst.rs
index f3c5f642a1..887ef878ad 100644
--- a/cranelift/codegen/meta/src/gen_inst.rs
+++ b/cranelift/codegen/meta/src/gen_inst.rs
@@ -75,14 +75,12 @@ fn gen_instruction_data(formats: &[&InstructionFormat], fmt: &mut Formatter) {
             fmtln!(fmt, "{} {{", format.name);
             fmt.indent(|fmt| {
                 fmt.line("opcode: Opcode,");
-                if format.typevar_operand.is_some() {
-                    if format.has_value_list {
-                        fmt.line("args: ValueList,");
-                    } else if format.num_value_operands == 1 {
-                        fmt.line("arg: Value,");
-                    } else {
-                        fmtln!(fmt, "args: [Value; {}],", format.num_value_operands);
-                    }
+                if format.has_value_list {
+                    fmt.line("args: ValueList,");
+                } else if format.num_value_operands == 1 {
+                    fmt.line("arg: Value,");
+                } else if format.num_value_operands > 0 {
+                    fmtln!(fmt, "args: [Value; {}],", format.num_value_operands);
                 }
                 for field in &format.imm_fields {
                     fmtln!(fmt, "{}: {},", field.member, field.kind.rust_type);
@@ -287,17 +285,17 @@ fn gen_instruction_data_impl(formats: &[&InstructionFormat], fmt: &mut Formatter
                     let name = format!("&Self::{}", format.name);
                     let mut members = vec!["opcode"];
 
-                    let args_eq = if format.typevar_operand.is_none() {
-                        None
-                    } else if format.has_value_list {
+                    let args_eq = if format.has_value_list {
                         members.push("args");
                         Some("args1.as_slice(pool) == args2.as_slice(pool)")
                     } else if format.num_value_operands == 1 {
                         members.push("arg");
                         Some("arg1 == arg2")
-                    } else {
+                    } else if format.num_value_operands > 0 {
                         members.push("args");
                         Some("args1 == args2")
+                    } else {
+                        None
                     };
 
                     for field in &format.imm_fields {
@@ -339,17 +337,17 @@ fn gen_instruction_data_impl(formats: &[&InstructionFormat], fmt: &mut Formatter
                     let name = format!("Self::{}", format.name);
                     let mut members = vec!["opcode"];
 
-                    let args = if format.typevar_operand.is_none() {
-                        "&()"
-                    } else if format.has_value_list {
+                    let args = if format.has_value_list {
                         members.push("ref args");
                         "args.as_slice(pool)"
                     } else if format.num_value_operands == 1 {
                         members.push("ref arg");
                         "arg"
-                    } else {
+                    } else if format.num_value_operands > 0{
                         members.push("ref args");
                         "args"
+                    } else {
+                        "&()"
                     };
 
                     for field in &format.imm_fields {