[all-commits] [llvm/llvm-project] 5cf784: [Clang][CodeGen] Don't emit assumptions if current...

[Yingwei Zheng via All-commits]

  Branch: refs/heads/release/19.x
  Home:   https://github.com/llvm/llvm-project
  Commit: 5cf78453b3de39247364ddf97b1c18c011283948
      https://github.com/llvm/llvm-project/commit/5cf78453b3de39247364ddf97b1c18c011283948
  Author: Yingwei Zheng <dtcxzyw2333 at gmail.com>
  Date:   2024-09-10 (Tue, 10 Sep 2024)

  Changed paths:
    M clang/lib/CodeGen/CGStmt.cpp
    M clang/test/SemaCXX/cxx23-assume.cpp

  Log Message:
  -----------
  [Clang][CodeGen] Don't emit assumptions if current block is unreachable. (#106936)

Fixes https://github.com/llvm/llvm-project/issues/106898.

When emitting an infinite loop, clang codegen will delete the whole
block and leave builder's current block as nullptr:

https://github.com/llvm/llvm-project/blob/837ee5b46a5f7f898f0de7e46a19600b896a0a1f/clang/lib/CodeGen/CGStmt.cpp#L597-L600

Then clang will create `zext (icmp slt %a, %b)` without parent block for
`a < b`. It will crash here:

https://github.com/llvm/llvm-project/blob/837ee5b46a5f7f898f0de7e46a19600b896a0a1f/clang/lib/CodeGen/CGExprScalar.cpp#L416-L420

Even if we disabled this optimization, it still crashes in
`Builder.CreateAssumption`:

https://github.com/llvm/llvm-project/blob/837ee5b46a5f7f898f0de7e46a19600b896a0a1f/llvm/lib/IR/IRBuilder.cpp#L551-L561

This patch disables assumptions emission if current block is null.

(cherry picked from commit c94bd96c277e0b48e198fdc831bb576d9a04aced)



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