wasm-mutate: Add a mutator to remove items in a module

This commit adds a new mutator to `wasm-mutate` which can remove any of
these items in a module:

* Functions
* Tables
* Memories
* Tags
* Globals
* Types
* Data
* Elements

This pass is not currently a "gc" pass where a set of used references is
generated, but rather the mutator considers itself applicable if a wasm
module contains any of the above items. If, during removal of an item,
the item is actually used then the mutation aborts with "not
applicable". It's expected that drivers like `wasm-shrink` will try
again with different seeds which will try a different mutator or will
otherwise try to remove a different item.

The main complexity in this mutator is that almost the entire module
(including the code section) is entirely rewritten. This is because item
references via index are everywhere in a wasm module and all of them are
candidate for being updated.

Overall my original test case for when `wasm-shrink` was first added
does indeed get successfully reduced down further from before, removing
extraneous functions and globals. The function-in-question still isn't
shrunk much but I believe that's because the peephole and code motion
mutator don't understand simd yet so those mutations are not applicable.

This commit also removes the recently added data segment and element
segment mutators. Their functionality is folded into this new
`RemoveItemMutator` mutator and the code section is now also updated to
account for updating `{elem,data}.drop` references.

Author: alexcrichton

crates/wasm-encoder/src/code.rs

@@ -32,7 +32,7 @@ use std::borrow::Cow;
 ///
 /// let wasm_bytes = module.finish();
 /// ```
-#[derive(Clone, Debug)]
+#[derive(Clone, Default, Debug)]
 pub struct CodeSection {
     bytes: Vec<u8>,
     num_added: u32,
@@ -41,10 +41,7 @@ pub struct CodeSection {
 impl CodeSection {
     /// Create a new code section encoder.
     pub fn new() -> CodeSection {
-        CodeSection {
-            bytes: vec![],
-            num_added: 0,
-        }
+        CodeSection::default()
     }
 
     /// How many function bodies have been defined inside this section so far?
@@ -361,7 +358,7 @@ pub enum Instruction<'a> {
     F64Const(f64),
     I32Eqz,
     I32Eq,
-    I32Neq,
+    I32Ne,
     I32LtS,
     I32LtU,
     I32GtS,
@@ -372,7 +369,7 @@ pub enum Instruction<'a> {
     I32GeU,
     I64Eqz,
     I64Eq,
-    I64Neq,
+    I64Ne,
     I64LtS,
     I64LtU,
     I64GtS,
@@ -382,13 +379,13 @@ pub enum Instruction<'a> {
     I64GeS,
     I64GeU,
     F32Eq,
-    F32Neq,
+    F32Ne,
     F32Lt,
     F32Gt,
     F32Le,
     F32Ge,
     F64Eq,
-    F64Neq,
+    F64Ne,
     F64Lt,
     F64Gt,
     F64Le,
@@ -1022,7 +1019,7 @@ impl Instruction<'_> {
             }
             Instruction::I32Eqz => bytes.push(0x45),
             Instruction::I32Eq => bytes.push(0x46),
-            Instruction::I32Neq => bytes.push(0x47),
+            Instruction::I32Ne => bytes.push(0x47),
             Instruction::I32LtS => bytes.push(0x48),
             Instruction::I32LtU => bytes.push(0x49),
             Instruction::I32GtS => bytes.push(0x4A),
@@ -1033,7 +1030,7 @@ impl Instruction<'_> {
             Instruction::I32GeU => bytes.push(0x4F),
             Instruction::I64Eqz => bytes.push(0x50),
             Instruction::I64Eq => bytes.push(0x51),
-            Instruction::I64Neq => bytes.push(0x52),
+            Instruction::I64Ne => bytes.push(0x52),
             Instruction::I64LtS => bytes.push(0x53),
             Instruction::I64LtU => bytes.push(0x54),
             Instruction::I64GtS => bytes.push(0x55),
@@ -1043,13 +1040,13 @@ impl Instruction<'_> {
             Instruction::I64GeS => bytes.push(0x59),
             Instruction::I64GeU => bytes.push(0x5A),
             Instruction::F32Eq => bytes.push(0x5B),
-            Instruction::F32Neq => bytes.push(0x5C),
+            Instruction::F32Ne => bytes.push(0x5C),
             Instruction::F32Lt => bytes.push(0x5D),
             Instruction::F32Gt => bytes.push(0x5E),
             Instruction::F32Le => bytes.push(0x5F),
             Instruction::F32Ge => bytes.push(0x60),
             Instruction::F64Eq => bytes.push(0x61),
-            Instruction::F64Neq => bytes.push(0x62),
+            Instruction::F64Ne => bytes.push(0x62),
             Instruction::F64Lt => bytes.push(0x63),
             Instruction::F64Gt => bytes.push(0x64),
             Instruction::F64Le => bytes.push(0x65),

crates/wasm-encoder/src/data.rs

@@ -30,7 +30,7 @@ use super::*;
 ///
 /// let wasm_bytes = module.finish();
 /// ```
-#[derive(Clone, Debug)]
+#[derive(Clone, Default, Debug)]
 pub struct DataSection {
     bytes: Vec<u8>,
     num_added: u32,
@@ -64,10 +64,7 @@ pub enum DataSegmentMode<'a> {
 impl DataSection {
     /// Create a new data section encoder.
     pub fn new() -> DataSection {
-        DataSection {
-            bytes: vec![],
-            num_added: 0,
-        }
+        DataSection::default()
     }
 
     /// How many segments have been defined inside this section so far?

crates/wasm-encoder/src/elements.rs

@@ -33,7 +33,7 @@ use super::*;
 ///
 /// let wasm_bytes = module.finish();
 /// ```
-#[derive(Clone, Debug)]
+#[derive(Clone, Default, Debug)]
 pub struct ElementSection {
     bytes: Vec<u8>,
     num_added: u32,
@@ -94,10 +94,7 @@ pub struct ElementSegment<'a> {
 impl ElementSection {
     /// Create a new element section encoder.
     pub fn new() -> ElementSection {
-        ElementSection {
-            bytes: vec![],
-            num_added: 0,
-        }
+        ElementSection::default()
     }
 
     /// How many segments have been defined inside this section so far?

crates/wasm-encoder/src/exports.rs

@@ -26,7 +26,7 @@ use super::*;
 ///
 /// let wasm_bytes = module.finish();
 /// ```
-#[derive(Clone, Debug)]
+#[derive(Clone, Default, Debug)]
 pub struct ExportSection {
     bytes: Vec<u8>,
     num_added: u32,
@@ -35,10 +35,7 @@ pub struct ExportSection {
 impl ExportSection {
     /// Create a new export section encoder.
     pub fn new() -> ExportSection {
-        ExportSection {
-            bytes: vec![],
-            num_added: 0,
-        }
+        ExportSection::default()
     }
 
     /// How many exports have been defined inside this section so far?

crates/wasm-encoder/src/functions.rs

@@ -20,7 +20,7 @@ use super::*;
 ///
 /// let wasm_bytes = module.finish();
 /// ```
-#[derive(Clone, Debug)]
+#[derive(Clone, Default, Debug)]
 pub struct FunctionSection {
     bytes: Vec<u8>,
     num_added: u32,
@@ -29,10 +29,7 @@ pub struct FunctionSection {
 impl FunctionSection {
     /// Construct a new function section encoder.
     pub fn new() -> FunctionSection {
-        FunctionSection {
-            bytes: vec![],
-            num_added: 0,
-        }
+        FunctionSection::default()
     }
 
     /// How many functions have been defined inside this section so far?

crates/wasm-encoder/src/globals.rs

@@ -21,7 +21,7 @@ use super::*;
 ///
 /// let wasm_bytes = module.finish();
 /// ```
-#[derive(Clone, Debug)]
+#[derive(Clone, Default, Debug)]
 pub struct GlobalSection {
     bytes: Vec<u8>,
     num_added: u32,
@@ -30,10 +30,7 @@ pub struct GlobalSection {
 impl GlobalSection {
     /// Create a new global section encoder.
     pub fn new() -> GlobalSection {
-        GlobalSection {
-            bytes: vec![],
-            num_added: 0,
-        }
+        GlobalSection::default()
     }
 
     /// How many globals have been defined inside this section so far?

crates/wasm-encoder/src/imports.rs

@@ -24,7 +24,7 @@ use std::convert::TryFrom;
 ///
 /// let wasm_bytes = module.finish();
 /// ```
-#[derive(Clone, Debug)]
+#[derive(Clone, Default, Debug)]
 pub struct ImportSection {
     bytes: Vec<u8>,
     num_added: u32,
@@ -33,10 +33,7 @@ pub struct ImportSection {
 impl ImportSection {
     /// Construct a new import section encoder.
     pub fn new() -> ImportSection {
-        ImportSection {
-            bytes: vec![],
-            num_added: 0,
-        }
+        ImportSection::default()
     }
 
     /// How many imports have been defined inside this section so far?

crates/wasm-encoder/src/memories.rs

@@ -19,7 +19,7 @@ use super::*;
 ///
 /// let wasm_bytes = module.finish();
 /// ```
-#[derive(Clone, Debug)]
+#[derive(Clone, Default, Debug)]
 pub struct MemorySection {
     bytes: Vec<u8>,
     num_added: u32,
@@ -28,10 +28,7 @@ pub struct MemorySection {
 impl MemorySection {
     /// Create a new memory section encoder.
     pub fn new() -> MemorySection {
-        MemorySection {
-            bytes: vec![],
-            num_added: 0,
-        }
+        MemorySection::default()
     }
 
     /// How many memories have been defined inside this section so far?

crates/wasm-encoder/src/tables.rs

@@ -19,7 +19,7 @@ use super::*;
 ///
 /// let wasm_bytes = module.finish();
 /// ```
-#[derive(Clone, Debug)]
+#[derive(Clone, Default, Debug)]
 pub struct TableSection {
     bytes: Vec<u8>,
     num_added: u32,
@@ -28,10 +28,7 @@ pub struct TableSection {
 impl TableSection {
     /// Construct a new table section encoder.
     pub fn new() -> TableSection {
-        TableSection {
-            bytes: vec![],
-            num_added: 0,
-        }
+        TableSection::default()
     }
 
     /// How many tables have been defined inside this section so far?

crates/wasm-encoder/src/tags.rs

@@ -19,7 +19,7 @@ use std::convert::TryFrom;
 ///
 /// let wasm_bytes = module.finish();
 /// ```
-#[derive(Clone, Debug)]
+#[derive(Clone, Default, Debug)]
 pub struct TagSection {
     bytes: Vec<u8>,
     num_added: u32,
@@ -28,10 +28,7 @@ pub struct TagSection {
 impl TagSection {
     /// Create a new tag section encoder.
     pub fn new() -> TagSection {
-        TagSection {
-            bytes: vec![],
-            num_added: 0,
-        }
+        TagSection::default()
     }
 
     /// How many tags have been defined inside this section so far?