[all-commits] [llvm/llvm-project] d6e6aa: [MemCpyOpt] Fixing Incorrect Code Motion while Han...

[Sam Elliott via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: d6e6aa8a42a96c09a78f0e02ecf50f12deda8024
      https://github.com/llvm/llvm-project/commit/d6e6aa8a42a96c09a78f0e02ecf50f12deda8024
  Author: Sam Elliott <selliott at lowrisc.org>
  Date:   2019-10-21 (Mon, 21 Oct 2019)

  Changed paths:
    M llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
    A llvm/test/Transforms/MemCpyOpt/aggregate-type-crash.ll

  Log Message:
  -----------
  [MemCpyOpt] Fixing Incorrect Code Motion while Handling Aggregate Type Values

Summary:
When MemCpyOpt is handling aggregate type values, if an instruction (let's call it P) between the targeting load (L) and store (S) clobbers the source pointer of L, it will try to hoist S before P. This process will also hoist S's data dependency instructions.

However, the current implementation has a bug that if one of S's dependency instructions is //also// a user of P, MemCpyOpt will not prevent it from being hoisted above P and cause a use-before-define error. For example, in the newly added test file (i.e. `aggregate-type-crash.ll`), it will try to hoist both `store %my_struct %1, %my_struct* %3` and its dependent, `%3 = bitcast i8* %2 to %my_struct*`, above `%2 = call i8* @my_malloc(%my_struct* %0)`. Creating the following BB:
```
entry:
  %1 = bitcast i8* %4 to %my_struct*
  %2 = bitcast %my_struct* %1 to i8*
  %3 = bitcast %my_struct* %0 to i8*
  call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 4 %2, i8* align 4 %3, i64 8, i1 false)
  %4 = call i8* @my_malloc(%my_struct* %0)
  ret void
```
Where there is a use-before-define error between `%1` and `%4`.

Update: The compiler for the Pony Programming Language [also encounter the same bug](https://github.com/ponylang/ponyc/issues/3140)

Patch by Min-Yih Hsu (myhsu)

Reviewers: eugenis, pcc, dblaikie, dneilson, t.p.northover, lattner

Reviewed By: eugenis

Subscribers: lenary, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66060

llvm-svn: 375403