Remove redundant range checks in Uri scheme parsing

[MihaZupan]

Now that #121262 is fixed, these are no longer needed (and are in fact just overhead)

[MihaZupan]

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[Copilot]

Pull request overview

This PR removes redundant bounds checks in Uri scheme parsing now that the JIT can elide dependent range checks correctly (per #121262), reducing unnecessary overhead in a hot parsing path.

Changes:

• Simplified the early validation condition in ParseSchemeCheckImplicitFile by removing now-redundant (uint)i / (uint)(i + 1) range checks.

[stephentoub]

🤖 Copilot Code Review — PR #124284

Holistic Assessment

Motivation: ✅ The PR is justified. PR #124242 (merged today) improved the JIT to recognize that (uint)(i + cns) < (uint)length implies (uint)(i + smallerCns) < (uint)length. The redundant checks being removed here were explicit hints for bounds check elimination that are no longer needed.

Approach: ✅ Correct approach. The remaining condition (uint)(i + 2) >= (uint)uriString.Length || colonOffset == 0 properly guards all subsequent accesses to uriString[i], uriString[i+1], and uriString[i+2] in lines 3567-3596.

Summary: ✅ LGTM. Simple, correct cleanup that removes dead code following a JIT optimization. The change is a net positive — it removes unnecessary overhead and improves code clarity.

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Detailed Findings

✅ Correctness — Bounds checks remain valid

Verified that after the simplified guard at line 3555-3556, all subsequent accesses are safe:

• uriString[i] — accessed at lines 3570, 3586
• uriString[i + 1] — accessed at lines 3567, 3583, 3589
• uriString[i + 2] — accessed at line 3572

The check (uint)(i + 2) >= (uint)uriString.Length returning early ensures i, i+1, and i+2 are all valid indices when execution continues past the guard.

✅ JIT Fix Verification — Dependency merged

Confirmed that PR #124242 ("Remove bounds checks for 'i + cns < len' pattern") was merged at 2026-02-11T16:18:03Z, which is the prerequisite for this cleanup.

💡 Minor — Comment could be removed

The comment // NB: A string must have at least 3 characters and at least 1 before ':' at line 3554 is still accurate, but the now-deleted comment // Redundant checks to eliminate range checks below is the one that explained why those checks existed. No action needed since the deleted lines and their comment are being removed together.