[llvm] AMDGPU: Add baseline tests for bitcast + readlane intrinsics (PR #128493)

[Matt Arsenault via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -mtriple=amdgcn-amd-amdhsa -mcpu=gfx1010 -passes=instcombine -S < %s | FileCheck %s
+
+define i32 @test_bitcast_f32_to_i32_readfirstlane(float %val) {
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arsenm wrote:

It won't be a negative test, the divergence does not matter 

https://github.com/llvm/llvm-project/pull/128493