winch: Small clean-up for x64 (#5691)

This commit contains a small set of clean up items for x64.

Notably:

* Adds filetests
* Documents why 16 for the arg base offset abi implementation, for clarity.
* Fixes a bug in the spill implementation caught while anlyzing the
filetests results. The fix consists of emitting a load instead of a store into
the scratch register before spiiling its value.
* Remove dead code for pretty printing registers which is not needed anymore
since we now have proper disassembly.

winch/codegen/src/isa/reg.rs

@@ -27,11 +27,6 @@ impl Reg {
         Self::new(PReg::new(enc, RegClass::Float))
     }
 
-    /// Get the class of the underlying register.
-    pub fn class(self) -> RegClass {
-        self.0.class()
-    }
-
     /// Get the encoding of the underlying register.
     pub fn hw_enc(self) -> u8 {
         self.0.hw_enc() as u8

winch/codegen/src/isa/x64/abi.rs

@@ -40,6 +40,15 @@ impl ABI for X64ABI {
     }
 
     fn arg_base_offset(&self) -> u8 {
+        // Two 8-byte slots, one for the return address and another
+        // one for the frame pointer.
+        // ┌──────────┬───────── Argument base
+        // │   Ret    │
+        // │   Addr   │
+        // ├──────────┼
+        // │          │
+        // │   FP     │
+        // └──────────┴
         16
     }
 

winch/codegen/src/isa/x64/masm.rs

@@ -124,6 +124,8 @@ impl Masm for MacroAssembler {
     }
 
     fn epilogue(&mut self, locals_size: u32) {
+        assert!(self.sp_offset == locals_size);
+
         let rsp = rsp();
         if locals_size > 0 {
             self.asm.add_ir(locals_size as i32, rsp, OperandSize::S64);

winch/codegen/src/isa/x64/regs.rs

@@ -142,97 +142,3 @@ const NON_ALLOCATABLE_GPR: u32 = (1 << ENC_RBP) | (1 << ENC_RSP) | (1 << ENC_R11
 
 /// Bitmask to represent the available general purpose registers.
 pub(crate) const ALL_GPR: u32 = ALLOCATABLE_GPR & !NON_ALLOCATABLE_GPR;
-
-// Temporarily removing the % from the register name
-// for debugging purposes only until winch gets disasm
-// support.
-pub(crate) fn reg_name(reg: Reg, size: u8) -> &'static str {
-    match reg.class() {
-        RegClass::Int => match (reg.hw_enc() as u8, size) {
-            (ENC_RAX, 8) => "rax",
-            (ENC_RAX, 4) => "eax",
-            (ENC_RAX, 2) => "ax",
-            (ENC_RAX, 1) => "al",
-            (ENC_RBX, 8) => "rbx",
-            (ENC_RBX, 4) => "ebx",
-            (ENC_RBX, 2) => "bx",
-            (ENC_RBX, 1) => "bl",
-            (ENC_RCX, 8) => "rcx",
-            (ENC_RCX, 4) => "ecx",
-            (ENC_RCX, 2) => "cx",
-            (ENC_RCX, 1) => "cl",
-            (ENC_RDX, 8) => "rdx",
-            (ENC_RDX, 4) => "edx",
-            (ENC_RDX, 2) => "dx",
-            (ENC_RDX, 1) => "dl",
-            (ENC_RSI, 8) => "rsi",
-            (ENC_RSI, 4) => "esi",
-            (ENC_RSI, 2) => "si",
-            (ENC_RSI, 1) => "sil",
-            (ENC_RDI, 8) => "rdi",
-            (ENC_RDI, 4) => "edi",
-            (ENC_RDI, 2) => "di",
-            (ENC_RDI, 1) => "dil",
-            (ENC_RBP, 8) => "rbp",
-            (ENC_RBP, 4) => "ebp",
-            (ENC_RBP, 2) => "bp",
-            (ENC_RBP, 1) => "bpl",
-            (ENC_RSP, 8) => "rsp",
-            (ENC_RSP, 4) => "esp",
-            (ENC_RSP, 2) => "sp",
-            (ENC_RSP, 1) => "spl",
-            (ENC_R8, 8) => "r8",
-            (ENC_R8, 4) => "r8d",
-            (ENC_R8, 2) => "r8w",
-            (ENC_R8, 1) => "r8b",
-            (ENC_R9, 8) => "r9",
-            (ENC_R9, 4) => "r9d",
-            (ENC_R9, 2) => "r9w",
-            (ENC_R9, 1) => "r9b",
-            (ENC_R10, 8) => "r10",
-            (ENC_R10, 4) => "r10d",
-            (ENC_R10, 2) => "r10w",
-            (ENC_R10, 1) => "r10b",
-            (ENC_R11, 8) => "r11",
-            (ENC_R11, 4) => "r11d",
-            (ENC_R11, 2) => "r11w",
-            (ENC_R11, 1) => "r11b",
-            (ENC_R12, 8) => "r12",
-            (ENC_R12, 4) => "r12d",
-            (ENC_R12, 2) => "r12w",
-            (ENC_R12, 1) => "r12b",
-            (ENC_R13, 8) => "r13",
-            (ENC_R13, 4) => "r13d",
-            (ENC_R13, 2) => "r13w",
-            (ENC_R13, 1) => "r13b",
-            (ENC_R14, 8) => "r14",
-            (ENC_R14, 4) => "r14d",
-            (ENC_R14, 2) => "r14w",
-            (ENC_R14, 1) => "r14b",
-            (ENC_R15, 8) => "r15",
-            (ENC_R15, 4) => "r15d",
-            (ENC_R15, 2) => "r15w",
-            (ENC_R15, 1) => "r15b",
-            _ => panic!("Invalid Reg: {:?}", reg),
-        },
-        RegClass::Float => match reg.hw_enc() {
-            0 => "xmm0",
-            1 => "xmm1",
-            2 => "xmm2",
-            3 => "xmm3",
-            4 => "xmm4",
-            5 => "xmm5",
-            6 => "xmm6",
-            7 => "xmm7",
-            8 => "xmm8",
-            9 => "xmm9",
-            10 => "xmm10",
-            11 => "xmm11",
-            12 => "xmm12",
-            13 => "xmm13",
-            14 => "xmm14",
-            15 => "xmm15",
-            _ => panic!("Invalid Reg: {:?}", reg),
-        },
-    }
-}

winch/codegen/src/regalloc.rs

@@ -134,9 +134,7 @@ impl RegAlloc {
                     .get_local(*index)
                     .expect("valid local at slot");
                 let addr = context.masm.local_address(&slot);
-                context
-                    .masm
-                    .store(RegImm::reg(self.scratch), addr, slot.ty.into());
+                context.masm.load(addr, self.scratch, slot.ty.into());
                 let offset = context.masm.push(self.scratch);
                 *v = Val::Memory(offset);
             }