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asm: Work around LLVM bug on AArch64 #103897

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Nov 4, 2022
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asm: Work around LLVM bug on AArch64 #103897

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57 changes: 54 additions & 3 deletions compiler/rustc_codegen_llvm/src/asm.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -496,6 +496,44 @@ fn xmm_reg_index(reg: InlineAsmReg) -> Option<u32> {
}
}

/// If the register is an AArch64 integer register then return its index.
fn a64_reg_index(reg: InlineAsmReg) -> Option<u32> {
match reg {
InlineAsmReg::AArch64(AArch64InlineAsmReg::x0) => Some(0),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x1) => Some(1),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x2) => Some(2),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x3) => Some(3),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x4) => Some(4),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x5) => Some(5),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x6) => Some(6),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x7) => Some(7),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x8) => Some(8),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x9) => Some(9),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x10) => Some(10),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x11) => Some(11),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x12) => Some(12),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x13) => Some(13),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x14) => Some(14),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x15) => Some(15),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x16) => Some(16),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x17) => Some(17),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x18) => Some(18),
// x19 is reserved
InlineAsmReg::AArch64(AArch64InlineAsmReg::x20) => Some(20),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x21) => Some(21),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x22) => Some(22),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x23) => Some(23),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x24) => Some(24),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x25) => Some(25),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x26) => Some(26),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x27) => Some(27),
InlineAsmReg::AArch64(AArch64InlineAsmReg::x28) => Some(28),
// x29 is reserved
InlineAsmReg::AArch64(AArch64InlineAsmReg::x30) => Some(30),
_ => None,
}
}

/// If the register is an AArch64 vector register then return its index.
fn a64_vreg_index(reg: InlineAsmReg) -> Option<u32> {
match reg {
Expand Down Expand Up @@ -526,6 +564,22 @@ fn reg_to_llvm(reg: InlineAsmRegOrRegClass, layout: Option<&TyAndLayout<'_>>) ->
'x'
};
format!("{{{}mm{}}}", class, idx)
} else if let Some(idx) = a64_reg_index(reg) {
let class = if let Some(layout) = layout {
match layout.size.bytes() {
8 => 'x',
_ => 'w',
}
} else {
// We use i32 as the type for discarded outputs
'w'
};
if class == 'x' && reg == InlineAsmReg::AArch64(AArch64InlineAsmReg::x30) {
// LLVM doesn't recognize x30. use lr instead.
"{lr}".to_string()
} else {
format!("{{{}{}}}", class, idx)
}
} else if let Some(idx) = a64_vreg_index(reg) {
let class = if let Some(layout) = layout {
match layout.size.bytes() {
Expand All @@ -541,9 +595,6 @@ fn reg_to_llvm(reg: InlineAsmRegOrRegClass, layout: Option<&TyAndLayout<'_>>) ->
'q'
};
format!("{{{}{}}}", class, idx)
} else if reg == InlineAsmReg::AArch64(AArch64InlineAsmReg::x30) {
// LLVM doesn't recognize x30
"{lr}".to_string()
} else if reg == InlineAsmReg::Arm(ArmInlineAsmReg::r14) {
// LLVM doesn't recognize r14
"{lr}".to_string()
Expand Down
16 changes: 16 additions & 0 deletions src/test/ui/asm/aarch64/llvm-58384.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,16 @@
// only-aarch64
// run-pass
// needs-asm-support

// Test that we properly work around this LLVM issue:
// https://github.com/llvm/llvm-project/issues/58384

use std::arch::asm;

fn main() {
let a: i32;
unsafe {
asm!("", inout("x0") 435 => a);
}
assert_eq!(a, 435);
}