f9865a08bc
This optimizes a common pattern like:
if s != "" {
...
}
to:
if len(s) != 0 {
...
}
This avoids a runtime call and thus produces slightly better code.
87 строки
2,4 КиБ
Go
87 строки
2,4 КиБ
Go
package transform
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// This file implements several small optimizations of runtime calls.
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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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// OptimizeStringEqual transforms runtime.stringEqual(...) calls into simple
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// integer comparisons if at least one of the sides of the comparison is zero.
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// Ths converts str == "" into len(str) == 0 and "" == "" into false.
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func OptimizeStringEqual(mod llvm.Module) {
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stringEqual := mod.NamedFunction("runtime.stringEqual")
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if stringEqual.IsNil() {
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// nothing to optimize
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return
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}
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builder := mod.Context().NewBuilder()
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defer builder.Dispose()
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for _, call := range getUses(stringEqual) {
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str1len := call.Operand(1)
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str2len := call.Operand(3)
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zero := llvm.ConstInt(str1len.Type(), 0, false)
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if str1len == zero || str2len == zero {
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builder.SetInsertPointBefore(call)
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icmp := builder.CreateICmp(llvm.IntEQ, str1len, str2len, "")
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call.ReplaceAllUsesWith(icmp)
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call.EraseFromParentAsInstruction()
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continue
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}
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}
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}
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