0003-Teach-rustc-about-the-Xtensa-call-ABI.patch

From bfc577ab2208db442ee7d356a21ae9c78e2b2d25 Mon Sep 17 00:00:00 2001
From: Scott Mabin <scott@mabez.dev>
Date: Sat, 12 Sep 2020 23:31:14 +0100
Subject: [PATCH 3/5] Teach rustc about the Xtensa call ABI.

---
 compiler/rustc_target/src/abi/call/mod.rs    |   2 +
 compiler/rustc_target/src/abi/call/xtensa.rs | 110 +++++++++++++++++++
 2 files changed, 112 insertions(+)
 create mode 100644 compiler/rustc_target/src/abi/call/xtensa.rs

diff --git a/compiler/rustc_target/src/abi/call/mod.rs b/compiler/rustc_target/src/abi/call/mod.rs
index 9c49922c286..5045e9d5d4d 100644
--- a/compiler/rustc_target/src/abi/call/mod.rs
+++ b/compiler/rustc_target/src/abi/call/mod.rs
@@ -7,6 +7,7 @@
 mod arm;
 mod avr;
 mod hexagon;
+mod xtensa;
 mod mips;
 mod mips64;
 mod msp430;
@@ -636,6 +637,7 @@ pub fn adjust_for_cabi<C>(&mut self, cx: &C, abi: spec::abi::Abi) -> Result<(),
             "nvptx" => nvptx::compute_abi_info(self),
             "nvptx64" => nvptx64::compute_abi_info(self),
             "hexagon" => hexagon::compute_abi_info(self),
+            "xtensa" => xtensa::compute_abi_info(cx, self),
             "riscv32" | "riscv64" => riscv::compute_abi_info(cx, self),
             "wasm32" => match cx.target_spec().os.as_str() {
                 "emscripten" | "wasi" => wasm32::compute_abi_info(cx, self),
diff --git a/compiler/rustc_target/src/abi/call/xtensa.rs b/compiler/rustc_target/src/abi/call/xtensa.rs
new file mode 100644
index 00000000000..422745d0a9e
--- /dev/null
+++ b/compiler/rustc_target/src/abi/call/xtensa.rs
@@ -0,0 +1,110 @@
+// reference: https://github.com/MabezDev/llvm-project/blob/xtensa_release_9.0.1_with_rust_patches-31-05-2020-cherry-pick/clang/lib/CodeGen/TargetInfo.cpp#L9668-L9767
+
+use crate::abi::call::{ArgAbi, FnAbi, Reg, Uniform};
+use crate::abi::{HasDataLayout, LayoutOf,  TyAndLayout, TyAndLayoutMethods,Abi, Size};
+use crate::spec::HasTargetSpec;
+
+const NUM_ARG_GPRS: u64 = 6;
+const MAX_ARG_IN_REGS_SIZE: u64 = 4 * 32;
+const MAX_RET_IN_REGS_SIZE: u64 = 2 * 32;
+
+fn classify_ret_ty<Ty>(arg: &mut ArgAbi<'_, Ty>, xlen: u64) {
+    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 arg_gprs_left);
+}
+
+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");
+
+    // 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 needed_arg_gprs = 1u64;
+
+    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;
+    }
+
+    if needed_arg_gprs > *arg_gprs_left {
+        must_use_stack = true;
+        needed_arg_gprs = *arg_gprs_left;
+    }
+    *arg_gprs_left -= needed_arg_gprs;
+
+    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 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 size <= xlen {
+            arg.cast_to(Reg::i32());
+            return;
+        } else if alignment == 2 * xlen {
+            arg.cast_to(Reg::i64());
+            return;
+        } else {
+            let total = Size::from_bits(((size + xlen - 1) / xlen) * xlen);
+            arg.cast_to(Uniform { unit: Reg::i32(), total });
+            return;
+        }
+    }
+
+    arg.make_indirect();
+}
+
+pub fn compute_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)
+where
+    Ty: TyAndLayoutMethods<'a, C> + Copy,
+    C: LayoutOf<Ty = Ty, TyAndLayout = TyAndLayout<'a, Ty>> + HasDataLayout + HasTargetSpec,
+{
+    let xlen = cx.data_layout().pointer_size.bits();
+
+    if !fn_abi.ret.is_ignore() {
+        classify_ret_ty(&mut fn_abi.ret, xlen);
+    }
+
+    let is_ret_indirect =
+        fn_abi.ret.is_indirect() || fn_abi.ret.layout.size.bits() > MAX_RET_IN_REGS_SIZE;
+
+    let mut arg_gprs_left = if is_ret_indirect { NUM_ARG_GPRS - 1 } else { NUM_ARG_GPRS };
+
+    for arg in &mut fn_abi.args {
+        if arg.is_ignore() {
+            continue;
+        }
+        let fixed = true;
+        classify_arg_ty(arg, xlen, fixed, &mut arg_gprs_left);
+    }
+}
\ No newline at end of file
-- 
2.26.3