llvm/test/CodeGen/X86/regalloc-csr-alias.mir

# RUN: llc -mtriple=i386 -passes=greedy,virt-reg-rewriter -regalloc-csr-cost-scale=100 %s -o - | FileCheck %s

# BL already requires saving EBX, so allocating BH adds no CSR cost. The
# control verifies that a genuinely unused CSR is still avoided.

--- |
  define i8 @bl_used() { ret i8 0 }
  define void @unused_csr() { ret void }
  declare void @callee()
...
---
name: bl_used
tracksRegLiveness: true
body: |
  ; CHECK-LABEL: name: bl_used
  ; CHECK: renamable $bh = MOV8ri 1
  ; CHECK-NEXT: CALLpcrel32 @callee
  ; CHECK-NEXT: TEST8rr killed renamable $bh, renamable $bh, implicit-def dead $eflags
  ; CHECK-NEXT: $al = COPY killed renamable $bl
  bb.0:
    liveins: $bl
    %0:gr8 = COPY $bl
    %1:gr8 = MOV8ri 1
    CALLpcrel32 @callee, csr_32, implicit $esp, implicit $ssp, implicit-def $esp, implicit-def $ssp
    TEST8rr %1, %1, implicit-def dead $eflags
    $al = COPY %0
    RET 0, $al
...
# No CSR is otherwise used, so rematerialize after the call instead of
# keeping the value in BH and incurring the cost of saving EBX.
---
name: unused_csr
tracksRegLiveness: true
body: |
  ; CHECK-LABEL: name: unused_csr
  ; CHECK: CALLpcrel32 @callee
  ; CHECK-NEXT: renamable $al = MOV8ri 1
  ; CHECK-NEXT: TEST8rr killed renamable $al, renamable $al, implicit-def dead $eflags
  bb.0:
    %0:gr8 = MOV8ri 1
    CALLpcrel32 @callee, csr_32, implicit $esp, implicit $ssp, implicit-def $esp, implicit-def $ssp
    TEST8rr %0, %0, implicit-def dead $eflags
    RET 0
...