Optimize away zero-length MCP/MCPI instructions

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

@@ -1,6 +1,8 @@
 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 +103,10 @@ 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/e2e_vm_tests/test_programs/should_pass/stdlib/vec_encoding_decoding/stdout.snap

@@ -7,7 +7,7 @@ output:
     Building test/src/e2e_vm_tests/test_programs/should_pass/stdlib/vec_encoding_decoding
    Compiling library std (test/src/e2e_vm_tests/reduced_std_libs/sway-lib-std-vec)
    Compiling script vec_encoding_decoding (test/src/e2e_vm_tests/test_programs/should_pass/stdlib/vec_encoding_decoding)
-    Finished release [optimized + fuel] target(s) [10.24 KB] in ???
+    Finished release [optimized + fuel] target(s) [10.232 KB] in ???
      Running 6 tests, filtered 0 tests
 
 tested -- vec_encoding_decoding
@@ -24,10 +24,10 @@ tested -- vec_encoding_decoding
       test nested_vec_non_trivial ... ok (???, 47654 gas)
            decoded log values:
 [[], [0], [0, 1], [0, 1, 2], [0, 1, 2, 3], [0, 1, 2, 3, 4], [0, 1, 2, 3, 4, 5], [0, 1, 2, 3, 4, 5, 6], [0, 1, 2, 3, 4, 5, 6, 7], [0, 1, 2, 3, 4, 5, 6, 7, 8]], log rb: 16171443785104013487
-      test vec_encode_zst ... ok (???, 3465 gas)
+      test vec_encode_zst ... ok (???, 3448 gas)
            decoded log values:
 [(), (), (), (), (), (), (), (), (), ()], log rb: 7172587179247292377
-      test nested_vec_zst ... ok (???, 23061 gas)
+      test nested_vec_zst ... ok (???, 22968 gas)
            decoded log values:
 [[], [()], [(), ()], [(), (), ()], [(), (), (), ()], [(), (), (), (), ()], [(), (), (), (), (), ()], [(), (), (), (), (), (), ()], [(), (), (), (), (), (), (), ()], [(), (), (), (), (), (), (), (), ()]], log rb: 15095959372321865352
 

test/src/ir_generation/tests/mcp_zero_len.sw

@@ -0,0 +1,26 @@
+// target-fuelvm
+script;
+
+fn main() -> u64 {
+    let src: u64 = 42;
+    let mut dst: u64 = 0;
+    asm(dst_ptr: __addr_of(dst), src_ptr: __addr_of(src), zero: 0u64) {
+        mcp dst_ptr src_ptr zero;
+    }
+    asm(dst_ptr: __addr_of(dst), src_ptr: __addr_of(src)) {
+        mcpi dst_ptr src_ptr i0;
+    }
+    dst
+}
+
+// ::check-ir::
+
+// check: asm(dst_ptr: $VAL, src_ptr: $VAL, zero: $VAL) -> ()
+// check: mcp
+// check: asm(dst_ptr: $VAL, src_ptr: $VAL) -> ()
+// check: mcpi
+
+// ::check-asm::
+//
+// not: mcp
+// not: mcpi