[stdlib] Encourage more inlining on String’s UTF-8 decoding fast path

lorentey · lorentey · commit 90d58fef8c05 · 2020-12-04T02:06:21.000-08:00
diff --git a/stdlib/public/core/String.swift b/stdlib/public/core/String.swift
@@ -458,6 +458,7 @@ extension String {
       contigBytes._providesContiguousBytesNoCopy
     {
       self = contigBytes.withUnsafeBytes { rawBufPtr in
+        Builtin.onFastPath() // encourage SIL Optimizer to inline this closure
         return String._fromUTF8Repairing(
           UnsafeBufferPointer(
             start: rawBufPtr.baseAddress?.assumingMemoryBound(to: UInt8.self),

Original file line number	Diff line number	Diff line change
`@@ -458,6 +458,7 @@ extension String {`
`458`	`458`	`contigBytes._providesContiguousBytesNoCopy`
`459`	`459`	`{`
`460`	`460`	`self = contigBytes.withUnsafeBytes { rawBufPtr in`
	`461`	`+ Builtin.onFastPath() // encourage SIL Optimizer to inline this closure`
`461`	`462`	`return String._fromUTF8Repairing(`
`462`	`463`	`UnsafeBufferPointer(`
`463`	`464`	`start: rawBufPtr.baseAddress?.assumingMemoryBound(to: UInt8.self),`