[PATCH] D11044: [ImplicitNullChecks] Be smarter in picking the memory op.

[Sanjoy Das]

sanjoy created this revision.
sanjoy added reviewers: atrick, JosephTremoulet, reames.
sanjoy added a subscriber: llvm-commits.

Before this change ImplicitNullChecks would only pick loads of the form:

```
   test Reg, Reg
   jz elsewhere
 fallthrough:
   movl 32(Reg), Reg2
```

but not (say)

```
   test Reg, Reg
   jz elsewhere
 fallthrough:
   inc Reg3
   movl 32(Reg), Reg2
```

This change teaches ImplicitNullChecks to look through "unrelated"
instructions like `inc Reg3` when searching for a load instruction
to convert to a trapping load.

http://reviews.llvm.org/D11044

Files:
  lib/CodeGen/ImplicitNullChecks.cpp
  test/CodeGen/X86/implicit-null-check-negative.ll
  test/CodeGen/X86/implicit-null-check.ll

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