Unable to mark ARM32's r14 register as clobbered in asm!

@Amanieu

I attempted to compile a crate containing the following expression:

unsafe { asm!("svc 0", lateout("r14") _); }

I expected it to compile successfully.

Instead, I received this error:

error: couldn't allocate output register for constraint '{r14}'

rustc --version --verbose:

rustc 1.52.0-nightly (3f5aee2d5 2021-02-12)
binary: rustc
commit-hash: 3f5aee2d5241139d808f4fdece0026603489afd1
commit-date: 2021-02-12
host: x86_64-unknown-linux-gnu
release: 1.52.0-nightly
LLVM version: 11.0.1

RUST_BACKTRACE=1 omitted, it did not produce anything else.

@Amanieu diagnosed the cause and offered a solution here.

While I try to spin up a rustc development environment, can someone point me to the tests for this code? I don't see any tests in the crate.

rust/compiler/rustc_codegen_llvm/src/asm.rs

Lines 487 to 490 in 21cbbdc

    
           } else if reg == InlineAsmReg::AArch64(AArch64InlineAsmReg::x30) { 
        
               // LLVM doesn't recognize x30 
        
               "{lr}".to_string() 
        
           } else {

rust/src/test/assembly/asm/aarch64-types.rs

Lines 99 to 108 in 21cbbdc

    
           // Regression test for #75761 
        
           // CHECK-LABEL: issue_75761: 
        
           // CHECK: str {{.*}}x30 
        
           // CHECK: //APP 
        
           // CHECK: //NO_APP 
        
           // CHECK: ldr {{.*}}x30 
        
           #[no_mangle] 
        
           pub unsafe fn issue_75761() { 
        
               asm!("", out("v0") _, out("x30") _); 
        
           }

@Amanieu

I think I have a working rustc development environment now. I'll try to fix this -- thank you @Amanieu for making this easy for me!

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Unable to mark ARM32's `r14` register as clobbered in `asm!` #82052

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	} else if reg == InlineAsmReg::AArch64(AArch64InlineAsmReg::x30) {
	// LLVM doesn't recognize x30
	"{lr}".to_string()
	} else {

	// Regression test for #75761
	// CHECK-LABEL: issue_75761:
	// CHECK: str {{.*}}x30
	// CHECK: //APP
	// CHECK: //NO_APP
	// CHECK: ldr {{.*}}x30
	#[no_mangle]
	pub unsafe fn issue_75761() {
	asm!("", out("v0") _, out("x30") _);
	}

Unable to mark ARM32's r14 register as clobbered in asm! #82052

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jrvanwhy commented on Feb 13, 2021

Amanieu commented on Feb 13, 2021

jrvanwhy commented on Feb 15, 2021

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Unable to mark ARM32's `r14` register as clobbered in `asm!` #82052