Optimize away zero-length MCP/MCPI instructions

sway-core/src/asm_generation/fuel/optimizations/misc.rs

@@ -1,6 +1,9 @@
 use super::super::abstract_instruction_set::AbstractInstructionSet;
 
-use crate::asm_lang::{JumpType, Op, OrganizationalOp, VirtualOp, VirtualRegister};
+use crate::asm_lang::{
+    virtual_register::ConstantRegister, JumpType, Op, OrganizationalOp, VirtualOp,
+    VirtualRegister,
+};
 
 use std::collections::HashSet;
 
@@ -101,6 +104,10 @@ impl AbstractInstructionSet {
             let remove = match &op.opcode {
                 Either::Left(VirtualOp::NOOP) => true,
                 Either::Left(VirtualOp::MOVE(a, b)) => a == b,
+                Either::Left(VirtualOp::MCP(_, _, len)) => {
+                    matches!(len, VirtualRegister::Constant(ConstantRegister::Zero))
+                }
+                Either::Left(VirtualOp::MCPI(_, _, imm)) => imm.value() == 0,
                 _ => false,
             };
 

test/src/ir_generation/tests/mcp_zero_len.sw

@@ -0,0 +1,20 @@
+// target-fuelvm
+script;
+
+fn main() -> u64 {
+    let src: u64 = 42;
+    let mut dst: u64 = 0;
+    asm(dst_ptr: dst, src_ptr: src, zero: 0u64) {
+        mcp dst_ptr src_ptr zero;
+    }
+    dst
+}
+
+// ::check-ir::
+
+// check: asm(dst_ptr: $VAL, src_ptr: $VAL, zero: $VAL) -> ()
+// check: mcp
+
+// ::check-asm::
+//
+// not: mcp