1 // Copyright 2018 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4
5 The codegen directory contains code generation tests for the gc
6 compiler.
7
8
9 - Introduction
10
11 The test harness compiles Go code inside files in this directory and
12 matches the generated assembly (the output of `go tool compile -S`)
13 against a set of regexps to be specified in comments that follow a
14 special syntax (described below). The test driver is implemented as
15 an action within the GOROOT/test test suite, called "asmcheck".
16
17 The codegen harness is part of the all.bash test suite, but for
18 performance reasons only the codegen tests for the host machine's
19 GOARCH are enabled by default, and only on GOOS=linux.
20
21 To perform comprehensive tests for all the supported architectures
22 (even on a non-Linux system), one can run the following command:
23
24 $ ../../bin/go test cmd/internal/testdir -run='Test/codegen' -all_codegen -v
25
26 This is recommended after any change that affect the compiler's code.
27
28 The test harness compiles the tests with the same go toolchain that is
29 used to run the test. After writing tests for a newly added codegen
30 transformation, it can be useful to first run the test harness with a
31 toolchain from a released Go version (and verify that the new tests
32 fail), and then re-running the tests using the devel toolchain.
33
34
35 - Regexps comments syntax
36
37 Instructions to match are specified inside plain comments that start
38 with an architecture tag, followed by a colon and a quoted Go-style
39 regexp to be matched. For example, the following test:
40
41 func Sqrt(x float64) float64 {
42 // amd64:"SQRTSD"
43 // arm64:"FSQRTD"
44 return math.Sqrt(x)
45 }
46
47 verifies that math.Sqrt calls are intrinsified to a SQRTSD instruction
48 on amd64, and to a FSQRTD instruction on arm64.
49
50 It is possible to put multiple architectures checks into the same
51 line, as:
52
53 // amd64:"SQRTSD" arm64:"FSQRTD"
54
55 although this form should be avoided when doing so would make the
56 regexps line excessively long and difficult to read.
57
58 Comments that are on their own line will be matched against the first
59 subsequent non-comment line. Inline comments are also supported; the
60 regexp will be matched against the code found on the same line:
61
62 func Sqrt(x float64) float64 {
63 return math.Sqrt(x) // arm:"SQRTD"
64 }
65
66 It's possible to specify a space-separated list of regexps to be
67 matched. For example, the following test:
68
69 func TZ8(n uint8) int {
70 // amd64:"BSFL" "ORL [$]256"
71 return bits.TrailingZeros8(n)
72 }
73
74 verifies that the code generated for a bits.TrailingZeros8 call on
75 amd64 contains both a "BSFL" instruction and an "ORL $256".
76
77 Note that spaces are special - they will match any sequence of
78 whitespace (including tabs) in the printed assembly.
79
80 Regexps can be quoted using either " or `. Special characters must be
81 escaped accordingly. All of these are accepted, and equivalent:
82
83 // amd64:"ADDQ \\$3"
84 // amd64:`ADDQ \$3`
85 // amd64:"ADDQ [$]3"
86
87 and they'll match this assembly line:
88
89 ADDQ $3
90
91 Negative matches can be specified using a - before the quoted regexp.
92 For example:
93
94 func MoveSmall() {
95 x := [...]byte{1, 2, 3, 4, 5, 6, 7}
96 copy(x[1:], x[:]) // arm64:-".*memmove"
97 }
98
99 verifies that NO memmove call is present in the assembly generated for
100 the copy() line.
101
102 The expected number of matches for the regexp can be specified using a
103 positive number:
104
105 func fb(a [4]int) (r [4]int) {
106 // amd64:2`MOVUPS[^,]+, X0$` 2`MOVUPS X0,[^\n]+$`
107 return a
108 }
109
110 - Architecture specifiers
111
112 There are three different ways to specify on which architecture a test
113 should be run:
114
115 * Specify only the architecture (eg: "amd64"). This indicates that the
116 check should be run on all the supported architecture variants. For
117 instance, arm checks will be run against all supported GOARM
118 variations (5,6,7).
119 * Specify both the architecture and a variant, separated by a slash
120 (eg: "arm/7"). This means that the check will be run only on that
121 specific variant.
122 * Specify the operating system, the architecture and the variant,
123 separated by slashes (eg: "plan9/386/sse2", "plan9/amd64/"). This is
124 needed in the rare case that you need to do a codegen test affected
125 by a specific operating system; by default, tests are compiled only
126 targeting linux.
127
128
129 - Remarks, and Caveats
130
131 -- Write small test functions
132
133 As a general guideline, test functions should be small, to avoid
134 possible interactions between unrelated lines of code that may be
135 introduced, for example, by the compiler's optimization passes.
136
137 Any given line of Go code could get assigned more instructions than it
138 may appear from reading the source. In particular, matching all MOV
139 instructions should be avoided; the compiler may add them for
140 unrelated reasons and this may render the test ineffective.
141
142 -- Line matching logic
143
144 Regexps are always matched from the start of the instructions line.
145 This means, for example, that the "MULQ" regexp is equivalent to
146 "^MULQ" (^ representing the start of the line), and it will NOT match
147 the following assembly line:
148
149 IMULQ $99, AX
150
151 To force a match at any point of the line, ".*MULQ" should be used.
152
153 For the same reason, a negative regexp like -"memmove" is not enough
154 to make sure that no memmove call is included in the assembly. A
155 memmove call looks like this:
156
157 CALL runtime.memmove(SB)
158
159 To make sure that the "memmove" symbol does not appear anywhere in the
160 assembly, the negative regexp to be used is -".*memmove".
161
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