blob: b3cfe1158208f9c14dd883d89c1a6f58353f6592 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
|
package transform
import (
"tinygo.org/x/go-llvm"
)
// OptimizeStringToBytes transforms runtime.stringToBytes(...) calls into const
// []byte slices whenever possible. This optimizes the following pattern:
//
// w.Write([]byte("foo"))
//
// where Write does not store to the slice.
func OptimizeStringToBytes(mod llvm.Module) {
stringToBytes := mod.NamedFunction("runtime.stringToBytes")
if stringToBytes.IsNil() {
// nothing to optimize
return
}
for _, call := range getUses(stringToBytes) {
strptr := call.Operand(0)
strlen := call.Operand(1)
// strptr is always constant because strings are always constant.
convertedAllUses := true
for _, use := range getUses(call) {
if use.IsAExtractValueInst().IsNil() {
// Expected an extractvalue, but this is something else.
convertedAllUses = false
continue
}
switch use.Type().TypeKind() {
case llvm.IntegerTypeKind:
// A length (len or cap). Propagate the length value.
use.ReplaceAllUsesWith(strlen)
use.EraseFromParentAsInstruction()
case llvm.PointerTypeKind:
// The string pointer itself.
if !isReadOnly(use) {
convertedAllUses = false
continue
}
use.ReplaceAllUsesWith(strptr)
use.EraseFromParentAsInstruction()
default:
// should not happen
panic("unknown return type of runtime.stringToBytes: " + use.Type().String())
}
}
if convertedAllUses {
// Call to runtime.stringToBytes can be eliminated: both the input
// and the output is constant.
call.EraseFromParentAsInstruction()
}
}
}
|
