[all-commits] [llvm/llvm-project] d91ea7: [AArch64] Move the branch relaxation pass after BT...

[Momchil Velikov via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: d91ea7fc6fd0cdd530e63c24db1d45253e1fdfdb
      https://github.com/llvm/llvm-project/commit/d91ea7fc6fd0cdd530e63c24db1d45253e1fdfdb
  Author: Momchil Velikov <momchil.velikov at arm.com>
  Date:   2019-11-06 (Wed, 06 Nov 2019)

  Changed paths:
    M llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
    M llvm/test/CodeGen/AArch64/O0-pipeline.ll
    M llvm/test/CodeGen/AArch64/O3-pipeline.ll
    A llvm/test/CodeGen/AArch64/bti-branch-relaxation.ll

  Log Message:
  -----------
  [AArch64] Move the branch relaxation pass after BTI insertion

Summary:
Inserting BTI instructions can push branch destinations out of range.

The branch relaxation pass itself cannot insert indirect branches since `TargetInstrInfo::insertIndirecrtBranch` is not implemented for AArch64 (guess +/-128 MB direct branch range is more than enough in practice).

Testing this is a bit tricky.

The original test case we have is 155kloc/6.1M. I've generated a test case using this program:
```

int main() {
  std::cout << R"src(int test();
void g0(), g1(), g2(), g3(), g4(), e();

void f(int v) {
  if ((test() & 2) == 0) {
  switch (v) {
  case 0:
    g0();
  case 1:
    g1();
  case 2:
    g2();
  case 3:
    g3();
  }
)src";

  const int N = 8176;

  for (int i = 0; i < N; ++i)
    std::cout << "    void h" << i << "();\n";
  for (int i = 0; i < N; ++i)
    std::cout << "    h" << i << "();\n";

  std::cout << R"src(
  } else {
    e();
  }
}
)src";
}
```
which is still a bit too much to commit as a regression test, IMHO.

Reviewers: t.p.northover, ostannard

Reviewed By: ostannard

Subscribers: kristof.beyls, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69118

Change-Id: Ide5c922bcde08ff4cf635da5e52365525a997a0a