llvm/test/CodeGen/AArch64/avoid-zero-copy.mir

# Check that we can remove the redundant save of constant registers such as $wzr
# RUN: llc -mtriple=aarch64-unknown-linux %s -verify-machineinstrs -start-before=machine-cp -o - | FileCheck %s --check-prefix ASM
# RUN: llc -mtriple=aarch64-unknown-linux %s -verify-machineinstrs -run-pass=machine-cp -o - | FileCheck %s
--- |
  target triple = "aarch64-unknown-linux"
  declare i32 @bar(i32) nounwind
  define i32 @foo() nounwind {
  ; ASM-LABEL: foo:
  ; ASM:       // %bb.0:
  ; ASM-NEXT:    str x30, [sp, #-16]! // 8-byte Folded Spill
  ; ASM-NEXT:    mov w0, wzr
  ; ASM-NEXT:    bl bar
  ; ASM-NEXT:    mov w0, wzr
  ; ASM-NEXT:    ldr x30, [sp], #16 // 8-byte Folded Reload
  ; ASM-NEXT:    ret
    call i32 @bar(i32 0)
    ret i32 0
  }
...
---
name: foo
body: |
  bb.0 (%ir-block.0):
    ; CHECK-LABEL: name: foo
    ; CHECK: ADJCALLSTACKDOWN 0, 0, implicit-def dead $sp, implicit $sp
    ; CHECK-NEXT: $w0 = COPY $wzr
    ; CHECK-NEXT: BL @bar, csr_aarch64_aapcs, implicit-def dead $lr, implicit $sp, implicit $w0, implicit-def $sp, implicit-def $w0
    ; CHECK-NEXT: ADJCALLSTACKUP 0, 0, implicit-def dead $sp, implicit $sp
    ; CHECK-NEXT: $w0 = COPY $wzr
    ; CHECK-NEXT: RET_ReallyLR implicit $w0
    ADJCALLSTACKDOWN 0, 0, implicit-def dead $sp, implicit $sp
    renamable $w19 = COPY $wzr
    $w0 = COPY renamable $w19
    BL @bar, csr_aarch64_aapcs, implicit-def dead $lr, implicit $sp, implicit $w0, implicit-def $sp, implicit-def $w0
    ADJCALLSTACKUP 0, 0, implicit-def dead $sp, implicit $sp
    $w0 = COPY killed renamable $w19
    RET_ReallyLR implicit $w0
...