From fd21eb18e96db98ff4f354f51d91051cf1533433 Mon Sep 17 00:00:00 2001
From: Johnathan Van Why <jrvanwhy@google.com>
Date: Sun, 14 Feb 2021 22:05:33 -0800
Subject: [PATCH] 32-bit ARM: Emit `lr` instead of `r14` when specified as an
 `asm!` output register.

On 32-bit ARM platforms, the register `r14` has the alias `lr`. When used as an output register in `asm!`, rustc canonicalizes the name to `r14`. LLVM only knows the register by the name `lr`, and rejects it. This changes rustc's LLVM code generation to output `lr` instead.
---
 compiler/rustc_codegen_llvm/src/asm.rs | 3 +++
 src/test/assembly/asm/arm-types.rs     | 9 +++++++++
 2 files changed, 12 insertions(+)

diff --git a/compiler/rustc_codegen_llvm/src/asm.rs b/compiler/rustc_codegen_llvm/src/asm.rs
index 8801211d51bc3..4aa25aae74760 100644
--- a/compiler/rustc_codegen_llvm/src/asm.rs
+++ b/compiler/rustc_codegen_llvm/src/asm.rs
@@ -487,6 +487,9 @@ fn reg_to_llvm(reg: InlineAsmRegOrRegClass, layout: Option<&TyAndLayout<'tcx>>)
             } 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()
             } else {
                 format!("{{{}}}", reg.name())
             }
diff --git a/src/test/assembly/asm/arm-types.rs b/src/test/assembly/asm/arm-types.rs
index 64b7c93cbc3e6..09901a7a39c08 100644
--- a/src/test/assembly/asm/arm-types.rs
+++ b/src/test/assembly/asm/arm-types.rs
@@ -91,6 +91,15 @@ pub unsafe fn sym_static() {
     asm!("adr r0, {}", sym extern_static);
 }
 
+// Regression test for #82052.
+// CHECK-LABEL: issue_82052
+// CHECK: push {{.*}}lr
+// CHECK: @APP
+// CHECK: @NO_APP
+pub unsafe fn issue_82052() {
+    asm!("", out("r14") _);
+}
+
 macro_rules! check {
     ($func:ident $ty:ident $class:ident $mov:literal) => {
         #[no_mangle]