65beddafe8
Unfortunately, while doing this I found that it doesn't actually apply in any real-world programs (tested with `make smoketest`), apparently because nil pointer checking messes with the functionattrs pass. I hope to fix that after moving to LLVM 9, which has an optimization that makes nil pointer checking easier to implement.
57 строки
1,5 КиБ
Go
57 строки
1,5 КиБ
Go
package transform
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import (
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"tinygo.org/x/go-llvm"
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)
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// OptimizeStringToBytes transforms runtime.stringToBytes(...) calls into const
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// []byte slices whenever possible. This optimizes the following pattern:
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//
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// w.Write([]byte("foo"))
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//
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// where Write does not store to the slice.
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func OptimizeStringToBytes(mod llvm.Module) {
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stringToBytes := mod.NamedFunction("runtime.stringToBytes")
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if stringToBytes.IsNil() {
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// nothing to optimize
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return
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}
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for _, call := range getUses(stringToBytes) {
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strptr := call.Operand(0)
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strlen := call.Operand(1)
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// strptr is always constant because strings are always constant.
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convertedAllUses := true
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for _, use := range getUses(call) {
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if use.IsAExtractValueInst().IsNil() {
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// Expected an extractvalue, but this is something else.
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convertedAllUses = false
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continue
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}
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switch use.Type().TypeKind() {
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case llvm.IntegerTypeKind:
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// A length (len or cap). Propagate the length value.
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use.ReplaceAllUsesWith(strlen)
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use.EraseFromParentAsInstruction()
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case llvm.PointerTypeKind:
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// The string pointer itself.
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if !isReadOnly(use) {
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convertedAllUses = false
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continue
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}
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use.ReplaceAllUsesWith(strptr)
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use.EraseFromParentAsInstruction()
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default:
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// should not happen
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panic("unknown return type of runtime.stringToBytes: " + use.Type().String())
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}
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}
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if convertedAllUses {
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// Call to runtime.stringToBytes can be eliminated: both the input
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// and the output is constant.
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call.EraseFromParentAsInstruction()
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}
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}
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}
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