Rollup merge of #133452 - taiki-e:hexagon-asm-pred, r=Amanieu

Support predicate registers (clobber-only) in Hexagon inline assembly

The result of the Hexagon instructions such as comparison, store conditional, etc. is stored in predicate registers (`p[0-3]`), but currently there is no way to mark it as clobbered in `asm!`.

This is also needed for `clobber_abi` (although implementing `clobber_abi` will require the addition of support for [several more register classes](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/Hexagon/HexagonRegisterInfo.cpp#L71-L90). see also #93335 (comment)).

Refs:
- [Section 6 "Conditional Execution" in Qualcomm Hexagon V73 Programmer’s Reference Manual](https://docs.qualcomm.com/bundle/publicresource/80-N2040-53_REV_AB_Qualcomm_Hexagon_V73_Programmers_Reference_Manual.pdf#page=90)
- [Register definition in LLVM](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/Hexagon/HexagonRegisterInfo.td#L155)

cc `@androm3da` (target maintainer of hexagon-unknown-{[none-elf](https://doc.rust-lang.org/nightly/rustc/platform-support/hexagon-unknown-none-elf.html#target-maintainers),[linux-musl](https://doc.rust-lang.org/nightly/rustc/platform-support/hexagon-unknown-linux-musl.html#target-maintainers)})

r? `@Amanieu`

`@rustbot` label +A-inline-assembly
(Currently there is no O-hexagon label...)

compiler/rustc_codegen_gcc/src/asm.rs

@@ -634,6 +634,9 @@ fn reg_to_gcc(reg: InlineAsmRegOrRegClass) -> ConstraintOrRegister {
             InlineAsmRegClass::Bpf(BpfInlineAsmRegClass::reg) => "r",
             InlineAsmRegClass::Bpf(BpfInlineAsmRegClass::wreg) => "w",
             InlineAsmRegClass::Hexagon(HexagonInlineAsmRegClass::reg) => "r",
+            InlineAsmRegClass::Hexagon(HexagonInlineAsmRegClass::preg) => {
+                unreachable!("clobber-only")
+            }
             InlineAsmRegClass::LoongArch(LoongArchInlineAsmRegClass::reg) => "r",
             InlineAsmRegClass::LoongArch(LoongArchInlineAsmRegClass::freg) => "f",
             InlineAsmRegClass::M68k(M68kInlineAsmRegClass::reg) => "r",
@@ -720,6 +723,9 @@ fn dummy_output_type<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, reg: InlineAsmRegCl
             cx.type_vector(cx.type_i64(), 2)
         }
         InlineAsmRegClass::Hexagon(HexagonInlineAsmRegClass::reg) => cx.type_i32(),
+        InlineAsmRegClass::Hexagon(HexagonInlineAsmRegClass::preg) => {
+            unreachable!("clobber-only")
+        }
         InlineAsmRegClass::LoongArch(LoongArchInlineAsmRegClass::reg) => cx.type_i32(),
         InlineAsmRegClass::LoongArch(LoongArchInlineAsmRegClass::freg) => cx.type_f32(),
         InlineAsmRegClass::Mips(MipsInlineAsmRegClass::reg) => cx.type_i32(),

compiler/rustc_codegen_llvm/src/asm.rs

@@ -645,6 +645,7 @@ fn reg_to_llvm(reg: InlineAsmRegOrRegClass, layout: Option<&TyAndLayout<'_>>) ->
             | Arm(ArmInlineAsmRegClass::qreg_low4) => "x",
             Arm(ArmInlineAsmRegClass::dreg) | Arm(ArmInlineAsmRegClass::qreg) => "w",
             Hexagon(HexagonInlineAsmRegClass::reg) => "r",
+            Hexagon(HexagonInlineAsmRegClass::preg) => unreachable!("clobber-only"),
             LoongArch(LoongArchInlineAsmRegClass::reg) => "r",
             LoongArch(LoongArchInlineAsmRegClass::freg) => "f",
             Mips(MipsInlineAsmRegClass::reg) => "r",
@@ -813,6 +814,7 @@ fn dummy_output_type<'ll>(cx: &CodegenCx<'ll, '_>, reg: InlineAsmRegClass) -> &'
         | Arm(ArmInlineAsmRegClass::qreg_low8)
         | Arm(ArmInlineAsmRegClass::qreg_low4) => cx.type_vector(cx.type_i64(), 2),
         Hexagon(HexagonInlineAsmRegClass::reg) => cx.type_i32(),
+        Hexagon(HexagonInlineAsmRegClass::preg) => unreachable!("clobber-only"),
         LoongArch(LoongArchInlineAsmRegClass::reg) => cx.type_i32(),
         LoongArch(LoongArchInlineAsmRegClass::freg) => cx.type_f32(),
         Mips(MipsInlineAsmRegClass::reg) => cx.type_i32(),

compiler/rustc_target/src/asm/hexagon.rs

@@ -7,6 +7,7 @@ use super::{InlineAsmArch, InlineAsmType, ModifierInfo};
 def_reg_class! {
     Hexagon HexagonInlineAsmRegClass {
         reg,
+        preg,
     }
 }
 
@@ -37,6 +38,7 @@ impl HexagonInlineAsmRegClass {
     ) -> &'static [(InlineAsmType, Option<Symbol>)] {
         match self {
             Self::reg => types! { _: I8, I16, I32, F32; },
+            Self::preg => &[],
         }
     }
 }
@@ -71,6 +73,10 @@ def_regs! {
         r26: reg = ["r26"],
         r27: reg = ["r27"],
         r28: reg = ["r28"],
+        p0: preg = ["p0"],
+        p1: preg = ["p1"],
+        p2: preg = ["p2"],
+        p3: preg = ["p3"],
         #error = ["r19"] =>
             "r19 is used internally by LLVM and cannot be used as an operand for inline asm",
         #error = ["r29", "sp"] =>

src/doc/unstable-book/src/language-features/asm-experimental-arch.md

@@ -30,6 +30,7 @@ This feature tracks `asm!` and `global_asm!` support for the following architect
 | NVPTX        | `reg32`        | None\*                             | `r`                  |
 | NVPTX        | `reg64`        | None\*                             | `l`                  |
 | Hexagon      | `reg`          | `r[0-28]`                          | `r`                  |
+| Hexagon      | `preg`         | `p[0-3]`                           | Only clobbers        |
 | PowerPC      | `reg`          | `r0`, `r[3-12]`, `r[14-28]`        | `r`                  |
 | PowerPC      | `reg_nonzero`  | `r[3-12]`, `r[14-28]`              | `b`                  |
 | PowerPC      | `freg`         | `f[0-31]`                          | `f`                  |
@@ -70,6 +71,7 @@ This feature tracks `asm!` and `global_asm!` support for the following architect
 | NVPTX        | `reg32`                         | None           | `i8`, `i16`, `i32`, `f32`               |
 | NVPTX        | `reg64`                         | None           | `i8`, `i16`, `i32`, `f32`, `i64`, `f64` |
 | Hexagon      | `reg`                           | None           | `i8`, `i16`, `i32`, `f32`               |
+| Hexagon      | `preg`                          | N/A            | Only clobbers                           |
 | PowerPC      | `reg`                           | None           | `i8`, `i16`, `i32`, `i64` (powerpc64 only) |
 | PowerPC      | `reg_nonzero`                   | None           | `i8`, `i16`, `i32`, `i64` (powerpc64 only) |
 | PowerPC      | `freg`                          | None           | `f32`, `f64`                            |

tests/codegen/asm/hexagon-clobbers.rs

@@ -0,0 +1,37 @@
+//@ revisions: hexagon
+//@[hexagon] compile-flags: --target hexagon-unknown-linux-musl
+//@[hexagon] needs-llvm-components: hexagon
+//@ compile-flags: -Zmerge-functions=disabled
+
+#![crate_type = "rlib"]
+#![feature(no_core, rustc_attrs, lang_items, asm_experimental_arch)]
+#![no_core]
+
+#[lang = "sized"]
+trait Sized {}
+
+#[rustc_builtin_macro]
+macro_rules! asm {
+    () => {};
+}
+
+// CHECK-LABEL: @flags_clobber
+// CHECK: call void asm sideeffect "", ""()
+#[no_mangle]
+pub unsafe fn flags_clobber() {
+    asm!("", options(nostack, nomem));
+}
+
+// CHECK-LABEL: @no_clobber
+// CHECK: call void asm sideeffect "", ""()
+#[no_mangle]
+pub unsafe fn no_clobber() {
+    asm!("", options(nostack, nomem, preserves_flags));
+}
+
+// CHECK-LABEL: @p0_clobber
+// CHECK: call void asm sideeffect "", "~{p0}"()
+#[no_mangle]
+pub unsafe fn p0_clobber() {
+    asm!("", out("p0") _, options(nostack, nomem, preserves_flags));
+}