Refactor call ABI.

src/librustc_target/abi/call/xtensa.rs

@@ -1,69 +1,81 @@
 // reference: https://github.com/espressif/clang-xtensa/commit/6fb488d2553f06029e6611cf81c6efbd45b56e47#diff-aa74ae1e1ab6b7149789237edb78e688R8450
 
 use crate::abi::call::{ArgAbi, FnAbi, Reg, Uniform};
+use crate::abi::{Abi, Size};
 
-const NUM_ARG_GPR: u64 = 6;
+const NUM_ARG_GPRS: u64 = 6;
 const MAX_ARG_IN_REGS_SIZE: u64 = 4 * 32;
-// const MAX_ARG_DIRECT_SIZE: u64 = MAX_ARG_IN_REGS_SIZE;
 const MAX_RET_IN_REGS_SIZE: u64 = 2 * 32;
 
 fn classify_ret_ty<Ty>(arg: &mut ArgAbi<'_, Ty>, xlen: u64) {
-    // The rules for return and argument types are the same, so defer to
-    // classify_arg_ty.
-    let mut remaining_gpr = 2;
+    if arg.is_ignore() {
+        return;
+    }
+
+    // The rules for return and argument types are the same,
+    // so defer to `classify_arg_ty`.
+    let mut arg_gprs_left = 2;
     let fixed = true;
-    classify_arg_ty(arg, xlen, fixed, &mut remaining_gpr);
+    classify_arg_ty(arg, xlen, fixed, &mut arg_gprs_left);
 }
 
-fn classify_arg_ty<Ty>(arg: &mut ArgAbi<'_, Ty>, xlen: u64, fixed: bool, remaining_gpr: &mut u64) {
-    assert!(*remaining_gpr <= NUM_ARG_GPR, "Arg GPR tracking underflow");
+fn classify_arg_ty<Ty>(arg: &mut ArgAbi<'_, Ty>, xlen: u64, fixed: bool, arg_gprs_left: &mut u64) {
+    assert!(*arg_gprs_left <= NUM_ARG_GPRS, "Arg GPR tracking underflow");
 
-    let arg_size = arg.layout.size;
-    let alignment = arg.layout.align.abi;
+    // Ignore empty structs/unions.
+    if arg.layout.is_zst() {
+        return;
+    }
+
+    let size = arg.layout.size.bits();
+    let needed_align = arg.layout.align.abi.bits();
+    let mut must_use_stack = false;
 
     // Determine the number of GPRs needed to pass the current argument
     // according to the ABI. 2*XLen-aligned varargs are passed in "aligned"
     // register pairs, so may consume 3 registers.
-    let mut required_gpr = 1u64;
+    let mut needed_arg_gprs = 1u64;
 
-    if !fixed && alignment.bits() == 2 * xlen {
-        required_gpr = 2 + (*remaining_gpr % 2);
-    } else if arg_size.bits() > xlen && arg_size.bits() <= MAX_ARG_IN_REGS_SIZE {
-        required_gpr = (arg_size.bits() + xlen - 1) / xlen;
+    if !fixed && needed_align == 2 * xlen {
+        needed_arg_gprs = 2 + (*arg_gprs_left % 2);
+    } else if size > xlen && size <= MAX_ARG_IN_REGS_SIZE {
+        needed_arg_gprs = (size + xlen - 1) / xlen;
     }
 
-    let mut stack_required = false;
-    if required_gpr > *remaining_gpr {
-        stack_required = true;
-        required_gpr = *remaining_gpr;
+    if needed_arg_gprs > *arg_gprs_left {
+        must_use_stack = true;
+        needed_arg_gprs = *arg_gprs_left;
     }
-    *remaining_gpr -= required_gpr;
+    *arg_gprs_left -= needed_arg_gprs;
 
-    if !arg.layout.is_aggregate() {
-        // All integral types are promoted to XLen width, unless passed on the
-        // stack.
-        if arg_size.bits() < xlen && !stack_required {
+    if !arg.layout.is_aggregate() && !matches!(arg.layout.abi, Abi::Vector { .. }) {
+        // All integral types are promoted to `xlen`
+        // width, unless passed on the stack.
+        if size < xlen && !must_use_stack {
             arg.extend_integer_width_to(xlen);
             return;
         }
 
         return;
     }
 
-    // Aggregates which are <= 4 * 32 will be passed in registers if possible,
-    // so coerce to integers.
-    if arg_size.bits() as u64 <= MAX_ARG_IN_REGS_SIZE {
-        // Use a single XLen int if possible, 2*XLen if 2*XLen alignment is
-        // required, and a 2-element XLen array if only XLen alignment is
+    // Aggregates which are <= 4 * 32 will be passed in
+    // registers if possible, so coerce to integers.
+    if size as u64 <= MAX_ARG_IN_REGS_SIZE {
+        let alignment = arg.layout.align.abi.bits();
+
+        // Use a single `xlen` int if possible, 2 * `xlen` if 2 * `xlen` alignment
+        // is required, and a 2-element `xlen` array if only `xlen` alignment is
         // required.
-        if arg_size.bits() <= xlen {
-            arg.cast_to(Uniform { unit: Reg::i32(), total: arg_size });
+        if size <= xlen {
+            arg.cast_to(Reg::i32());
             return;
-        } else if alignment.bits() == 2 * xlen {
-            arg.cast_to(Uniform { unit: Reg::i64(), total: arg_size });
+        } else if alignment == 2 * xlen {
+            arg.cast_to(Reg::i64());
             return;
         } else {
-            arg.extend_integer_width_to((arg_size.bits() + xlen - 1) / xlen);
+            let total = Size::from_bits(((size + xlen - 1) / xlen) * xlen);
+            arg.cast_to(Uniform { unit: Reg::i32(), total });
             return;
         }
     }
@@ -72,20 +84,15 @@ fn classify_arg_ty<Ty>(arg: &mut ArgAbi<'_, Ty>, xlen: u64, fixed: bool, remaini
 }
 
 pub fn compute_abi_info<Ty>(fty: &mut FnAbi<'_, Ty>, xlen: u64) {
-    if !fty.ret.is_ignore() {
-        classify_ret_ty(&mut fty.ret, xlen);
-    }
+    classify_ret_ty(&mut fty.ret, xlen);
 
-    let return_indirect =
+    let is_ret_indirect =
         fty.ret.is_indirect() || fty.ret.layout.size.bits() > MAX_RET_IN_REGS_SIZE;
 
-    let mut remaining_gpr = if return_indirect { NUM_ARG_GPR - 1 } else { NUM_ARG_GPR };
+    let mut arg_gprs_left = if is_ret_indirect { NUM_ARG_GPRS - 1 } else { NUM_ARG_GPRS };
 
     for arg in &mut fty.args {
-        if arg.is_ignore() {
-            continue;
-        }
         let fixed = true;
-        classify_arg_ty(arg, xlen, fixed, &mut remaining_gpr);
+        classify_arg_ty(arg, xlen, fixed, &mut arg_gprs_left);
     }
 }