[Do not merge][Flang][OpenMP] Fix OpenMP static scheduling when trip count is zero

[mjklemm]

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[z1-cciauto]

PSDB Link: https://compiler-ci.amd.com/job/compiler-psdb-amd-staging/3116

[Copilot]

Pull request overview

This PR fixes a bug in OpenMP static scheduling when the trip count is zero. The fix prevents incorrect upper bound values by explicitly checking for a zero trip count before storing the upper bound.

Key changes:

• Adds a zero trip count check before computing the upper bound
• Uses a select instruction to conditionally set the upper bound to zero when trip count is zero

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[z1-cciauto]

PSDB Link: https://compiler-ci.amd.com/job/compiler-psdb-amd-staging/3123