Ignore dead code

[turbolent]

Description

Don't just report, but also ignore dead code. This reduces checking time, and actually has the side-effect of improving errors: Checking dead code was poisoning the data flow analysis (a function activation's return info tracks if the function definitely returned/jumped/halted), so e.g. a missing return statement error was not reported.

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• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[codecov-commenter]

Codecov Report

Merging #1345 (0002edd) into master (b07c80c) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1345      +/-   ##
==========================================
- Coverage   75.70%   75.70%   -0.01%     
==========================================
  Files         280      280              
  Lines       38585    38584       -1     
==========================================
- Hits        29211    29210       -1     
  Misses       8028     8028              
  Partials     1346     1346              

Flag	Coverage Δ
unittests	75.70% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
runtime/sema/function_activations.go	93.93% <ø> (ø)
runtime/sema/check_block.go	100.00% <100.00%> (ø)

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[github-actions]

Cadence Benchstat comparison

This branch with compared with the base branch onflow:master commit b07c80c
The command for i in {1..N}; do go test ./... -run=XXX -bench=. -shuffle=on; done was used.
Bench tests were run a total of 7 times on each branch.

Results

	old.txt	new.txt
	time/op		delta
RuntimeResourceDictionaryValues-2	15.0ms ± 5%	14.7ms ± 1%	~	(p=0.318 n=7+7)
RuntimeFungibleTokenTransfer-2	1.20ms ±35%	1.31ms ±25%	~	(p=1.000 n=7+7)
ParseInfix-2	9.93µs ± 5%	9.67µs ± 1%	~	(p=0.053 n=7+7)
ParseDeploy/byte_array-2	22.6ms ± 6%	22.6ms ± 9%	~	(p=0.805 n=7+7)
ParseDeploy/decode_hex-2	1.17ms ± 2%	1.17ms ± 0%	~	(p=0.366 n=7+6)
QualifiedIdentifierCreation/One_level-2	2.68ns ± 0%	2.68ns ± 0%	~	(p=0.793 n=7+7)
QualifiedIdentifierCreation/Three_levels-2	141ns ± 4%	140ns ± 2%	~	(p=0.734 n=7+7)
ContractInterfaceFungibleToken-2	40.3µs ± 3%	40.0µs ± 2%	~	(p=0.310 n=6+6)
CheckContractInterfaceFungibleTokenConformance-2	135µs ± 4%	132µs ± 2%	~	(p=0.181 n=7+6)
NewInterpreter/new_interpreter-2	1.02µs ± 1%	1.02µs ± 1%	~	(p=0.589 n=6+6)
NewInterpreter/new_sub-interpreter-2	2.03µs ± 2%	2.03µs ± 1%	~	(p=0.805 n=7+6)
InterpretRecursionFib-2	2.47ms ± 3%	2.44ms ± 2%	~	(p=0.073 n=7+7)
ParseFungibleToken-2	186µs ± 3%	181µs ± 1%	−2.40%	(p=0.002 n=7+6)
ParseArray-2	14.1ms ± 5%	13.3ms ± 2%	−6.29%	(p=0.004 n=6+6)
	alloc/op		delta
RuntimeResourceDictionaryValues-2	4.05MB ± 0%	4.05MB ± 0%	~	(p=0.805 n=7+7)
RuntimeFungibleTokenTransfer-2	273kB ± 0%	273kB ± 0%	~	(p=0.477 n=7+7)
QualifiedIdentifierCreation/One_level-2	0.00B	0.00B	~	(all equal)
QualifiedIdentifierCreation/Three_levels-2	64.0B ± 0%	64.0B ± 0%	~	(all equal)
CheckContractInterfaceFungibleTokenConformance-2	65.7kB ± 0%	65.7kB ± 0%	~	(p=0.462 n=7+7)
NewInterpreter/new_interpreter-2	720B ± 0%	720B ± 0%	~	(all equal)
NewInterpreter/new_sub-interpreter-2	1.18kB ± 0%	1.18kB ± 0%	~	(all equal)
InterpretRecursionFib-2	1.24MB ± 0%	1.24MB ± 0%	~	(p=0.538 n=7+6)
ContractInterfaceFungibleToken-2	26.5kB ± 0%	26.5kB ± 0%	−0.00%	(p=0.042 n=7+6)
	allocs/op		delta
RuntimeResourceDictionaryValues-2	102k ± 0%	102k ± 0%	~	(p=0.685 n=7+7)
RuntimeFungibleTokenTransfer-2	4.54k ± 0%	4.54k ± 0%	~	(p=0.499 n=7+7)
QualifiedIdentifierCreation/One_level-2	0.00	0.00	~	(all equal)
QualifiedIdentifierCreation/Three_levels-2	2.00 ± 0%	2.00 ± 0%	~	(all equal)
ContractInterfaceFungibleToken-2	457 ± 0%	457 ± 0%	~	(all equal)
CheckContractInterfaceFungibleTokenConformance-2	1.07k ± 0%	1.07k ± 0%	~	(all equal)
NewInterpreter/new_interpreter-2	11.0 ± 0%	11.0 ± 0%	~	(all equal)
NewInterpreter/new_sub-interpreter-2	36.0 ± 0%	36.0 ± 0%	~	(all equal)
InterpretRecursionFib-2	25.0k ± 0%	25.0k ± 0%	~	(all equal)