[all-commits] [llvm/llvm-project] 26ebcd: [Clang][CodeGen] Avoid emitting poison immargs for...

[jpwang via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 26ebcddb8f886640b20a8643d5ff212f95f7bbd8
      https://github.com/llvm/llvm-project/commit/26ebcddb8f886640b20a8643d5ff212f95f7bbd8
  Author: jpwang <jpwang at smail.nju.edu.cn>
  Date:   2026-06-08 (Mon, 08 Jun 2026)

  Changed paths:
    M clang/lib/CodeGen/CGBuiltin.cpp
    A clang/test/CodeGen/prefetch-poison-arg.c

  Log Message:
  -----------
  [Clang][CodeGen] Avoid emitting poison immargs for __builtin_prefetch (#201623)

Fixes #201448

This PR fixes invalid clang CodeGen when lowering `__builtin_prefetch`
that is called with a constant expression that produces a poison value.

The code currently assumes that the immediate operands are
`ConstantInt`s. This is not always true as poison values may come from
UB expressions (e.g., `__builtin_prefetch(0, 2 >> 32)`) due to the use
of `EmitScalarExpr`. This would cause the subsequent downcast
`cast<ConstantInt>` in `SelectionDAGBuilder` to fail.

This PR replaces `EmitScalarExpr` with `EmitScalarOrConstFoldImmArg` to
obtain an integer constant instead of emitting a poison value for the
corresponding arguments of `llvm.prefetch`.

A regression test is also added to cover the poison immediate argument
case.

I used GPT-5.5 while working on this PR for understanding the issue and
drafting the PR description / test plan. The actual code changes and
tests are written by me, and I have noted the AI tool usage in the PR
description.



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