tree f98d69219d8620cea9240bd46670d0fc519cd990
parent b4c9e713fa40621c0f49b4a868a06d8bb6d06806
author Iris Shi <0.0@owo.li> 1778511098 +0800
committer GitHub <noreply@github.com> 1778511098 +0800
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[DAGCombiner] Fix abs(add) to abdu miscompile in foldABSToABD (#196782)

The abs(add(x, y)) → abdu(x, -y) fold added in #186659 is incorrect when
both operands are known non-negative and their sum does not overflow
signed.

When both x and y are non-negative and `x + y < 2^31`, `abs(x + y) = x +
y`, but `abdu(x, -y) = 2^32 - y - x ≠ x + y`.
For example, `abs(add(0, 1)) = 1`, but `abdu(0, -1) = 0xFFFFFFFF`. 

Related: #185467 #175801