[all-commits] [llvm/llvm-project] 514f5b: [ConstantFolding] Fix dropped bits in non-integer-...

[lijinpei-amd via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 514f5b766667c4c696b260f783403e8b41bc8798
      https://github.com/llvm/llvm-project/commit/514f5b766667c4c696b260f783403e8b41bc8798
  Author: lijinpei-amd <jinpli at amd.com>
  Date:   2026-06-09 (Tue, 09 Jun 2026)

  Changed paths:
    M llvm/lib/Analysis/ConstantFolding.cpp
    M llvm/test/Transforms/InstSimplify/bitcast-vector-fold.ll

  Log Message:
  -----------
  [ConstantFolding] Fix dropped bits in non-integer-ratio bitcast with undef lane (#202282)

When constant-folding a vector bitcast(e.g. <4 x i24> -> <3 x i32>), an
undef source element inserted a DstBitSize-wide zero placeholder into
the bit buffer. This could clobber defined source element, producing a
wrong result on big-endian targets.

Fix by inserting SrcBitSize-wide zero instead.

Alive2 proof:
  before (unsound): https://alive2.llvm.org/ce/z/R_ZQ75
  after  (verified): https://alive2.llvm.org/ce/z/VuV3mz



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