[Opt] [ir] [refactor] Remove exceptions from DIE pass

[TH3CHARLie]

Related issue = #1059

This is the only pass remained that can be modified simply, the others would require making changes to DelayedIRModifier(adding functions like replace_with). I'll make them in another PR.

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[xumingkuan]

Cool! Maybe also make die return if it modifies the IR so that passes like full_simplify can have a better sense of whether the IR is changed?

[codecov]

Codecov Report

Merging #1262 into master will increase coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1262      +/-   ##
==========================================
+ Coverage   84.78%   84.86%   +0.07%     
==========================================
  Files          18       18              
  Lines        3267     3271       +4     
  Branches      613      613              
==========================================
+ Hits         2770     2776       +6     
  Misses        360      360              
+ Partials      137      135       -2     

Impacted Files	Coverage Δ
python/taichi/lang/__init__.py	73.13% <0.00%> (+0.43%)	⬆️
python/taichi/lang/snode.py	77.33% <0.00%> (+1.97%)	⬆️

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[yuanming-hu]

LGTM! Thanks. Let's merge this after v0.6.11 is released. @xumingkuan Feel free to merge IR-optimization related PRs without my approval - you understand this part very well and I trust your decision.

[xumingkuan]

LGTM!