[PATCH] D48627: [ImplicitNullChecks] Check for rewrite of register used in 'test' instruction

[Surya Kumari Jangala via Phabricator via llvm-commits]

jskumari created this revision.
jskumari added reviewers: sanjoy, skatkov.
Herald added a subscriber: llvm-commits.

The following code pattern:

  mov %rax, %rcx
  test %rax, %rax
  %rax = ....
  je  throw_npe
  mov(%rcx), %r9
  mov(%rax), %r10

gets transformed into the following incorrect code after implicit null check pass:

   mov %rax, %rcx
  %rax = ....
  faulting_load_op("movl (%rax), %r10", throw_npe)
  mov(%rcx), %r9

For implicit null check pass, if the register that is checked for null value (ie, the register used in the 'test' instruction) is written into before the condition jump, we should avoid doing the optimization.


Repository:
  rL LLVM

https://reviews.llvm.org/D48627

Files:
  lib/CodeGen/ImplicitNullChecks.cpp
  test/CodeGen/X86/implicit-null-chk-reg-rewrite.mir

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