[llvm] [clang] [Instcombine] use zext's nneg flag for icmp folding (PR #70845)

[Léonard Oest O'Leary via cfe-commits]

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+// RUN: %clang_cc1 %s -O2 -triple=x86_64-apple-darwin -emit-llvm -o - | FileCheck %s
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leo-ard wrote:

Out of curiosity, why is end-to-end codegen with clang not used ? Is it too unstable ?

https://github.com/llvm/llvm-project/pull/70845