Yingwei Zheng 4997af98a0 [SimplifyCFG] Simplify nested branches (#97067) ...

This patch folds the following pattern (I don't know what to call this):
```
bb0:
  br i1 %cond1, label %bb1, label %bb2
bb1:
  br i1 %cond2, label %bb3, label %bb4
bb2:
  br i1 %cond2, label %bb4, label %bb3
bb3:
  ...
bb4:
  ...
```
into
```
bb0:
  %cond = xor i1 %cond1, %cond2
  br i1 %cond, label %bb4, label %bb3
bb3:
  ...
bb4:
  ...
```

Alive2: https://alive2.llvm.org/ce/z/5iOJEL
Closes https://github.com/llvm/llvm-project/issues/97022.
Closes https://github.com/llvm/llvm-project/issues/83417.

I found this pattern in some verilator-generated code, which is widely
used in RTL simulation. This fold will reduces branches and improves the
performance of CPU frontend. To my surprise, this pattern is also common
in C/C++ code base.
Affected libraries/applications:
cmake/cvc5/freetype/git/gromacs/jq/linux/openblas/openmpi/openssl/php/postgres/ruby/sqlite/wireshark/z3/...

2024-07-01 03:35:39 +08:00

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