1Checker is a testing tool which compiles a given test file and compares the 2state of the control-flow graph before and after each optimization pass 3against a set of assertions specified alongside the tests. 4 5Tests are written in Java or Smali, turned into DEX and compiled with the 6Optimizing compiler. "Check lines" are assertions formatted as comments of the 7source file. They begin with prefix "/// CHECK" or "## CHECK", respectively, 8followed by a pattern that the engine attempts to match in the compiler output. 9 10Assertions are tested in groups which correspond to the individual compiler 11passes. Each group of check lines therefore must start with a 'CHECK-START' 12header which specifies the output group it should be tested against. The group 13name must exactly match one of the groups recognized in the output (they can 14be listed with the '--list-passes' command-line flag). 15 16Matching of check lines is carried out in the order of appearance in the 17source file. There are three types of check lines: 18 - CHECK: Must match an output line which appears in the output group 19 later than lines matched against any preceeding checks. Output 20 lines must therefore match the check lines in the same order. 21 These are referred to as "in-order" checks in the code. 22 - CHECK-DAG: Must match an output line which appears in the output group 23 later than lines matched against any preceeding in-order checks. 24 In other words, the order of output lines does not matter 25 between consecutive DAG checks. 26 - CHECK-NOT: Must not match any output line which appears in the output group 27 later than lines matched against any preceeding checks and 28 earlier than lines matched against any subsequent checks. 29 Surrounding non-negative checks (or boundaries of the group) 30 therefore create a scope within which the assertion is verified. 31 - CHECK-NEXT: Must match the output line which comes right after the line which 32 matched the previous check. Cannot be used after any but the 33 in-order CHECK. 34 - CHECK-EVAL: Specifies a Python expression which must evaluate to 'True'. 35 36Check-line patterns are treated as plain text rather than regular expressions 37but are whitespace agnostic. 38 39Actual regex patterns can be inserted enclosed in '{{' and '}}' brackets. If 40curly brackets need to be used inside the body of the regex, they need to be 41enclosed in round brackets. For example, the pattern '{{foo{2}}}' will parse 42the invalid regex 'foo{2', but '{{(fo{2})}}' will match 'foo'. 43 44Regex patterns can be named and referenced later. A new variable is defined 45with '<<name:regex>>' and can be referenced with '<<name>>'. Variables are 46only valid within the scope of the defining group. Within a group they cannot 47be redefined or used undefined. 48 49Example: 50 The following assertions can be placed in a Java source file: 51 52 /// CHECK-START: int MyClass.MyMethod() constant_folding (after) 53 /// CHECK: <<ID:i\d+>> IntConstant {{11|22}} 54 /// CHECK: Return [<<ID>>] 55 56 The engine will attempt to match the check lines against the output of the 57 group named on the first line. Together they verify that the CFG after 58 constant folding returns an integer constant with value either 11 or 22. 59 60 61Of the language constructs above, 'CHECK-EVAL' lines support only referencing of 62variables. Any other surrounding text will be passed to Python's `eval` as is. 63 64Example: 65 /// CHECK-START: int MyClass.MyMethod() liveness (after) 66 /// CHECK: InstructionA liveness:<<VarA:\d+>> 67 /// CHECK: InstructionB liveness:<<VarB:\d+>> 68 /// CHECK-EVAL: <<VarA>> != <<VarB>> 69 70 71A group of check lines can be made architecture-specific by inserting '-<arch>' 72after the 'CHECK-START' keyword. The previous example can be updated to run for 73arm64 only with: 74 75Example: 76 /// CHECK-START-ARM64: int MyClass.MyMethod() constant_folding (after) 77 /// CHECK: <<ID:i\d+>> IntConstant {{11|22}} 78 /// CHECK: Return [<<ID>>] 79 80For convenience, several architectures can be specified as set after the 81'CHECK-START' keyword. Any listed architecture will match in that case, 82thereby avoiding to repeat the check lines if some, but not all architectures 83match. An example line looks like: 84 85 /// CHECK-START-{MIPS,ARM,ARM64}: int MyClass.MyMethod() constant_folding (after) 86