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cmd/compile: replace magic numbers "2" and "1" with named constant 

This was originally done for a #next-encoding-based check for
misbehaving loops, but it's a good idea anyhow because it makes
the code slightly easier to follow or change (we may decide to
check for errors the "other way" anyhow, later).

Change-Id: I2ba8f6e0f9146f0ff148a900eabdefd0fffebf8b
Reviewed-on: https://go-review.googlesource.com/c/go/+/540261
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
This commit is contained in:
David Chase 2023-11-07 16:37:17 -05:00
parent fdc21f3eaf
commit 6f5aba995f
1 changed files with 10 additions and 3 deletions
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13
src/cmd/compile/internal/rangefunc/rewrite.go
View File

@ -640,6 +640,13 @@ func (r *rewriter) editReturn(x *syntax.ReturnStmt) syntax.Stmt {
return bl
}
// perLoopStep is part of the encoding of loop-spanning control flow
// for function range iterators. Each multiple of two encodes a "return false"
// passing control to an enclosing iterator; a terminal value of 1 encodes
// "return true" (i.e., local continue) from the body function, and a terminal
// value of 0 encodes executing the remainder of the body function.
const perLoopStep = 2
// editBranch returns the replacement for the branch statement x,
// or x itself if it should be left alone.
// See the package doc comment above for more context.
@ -734,7 +741,7 @@ func (r *rewriter) editBranch(x *syntax.BranchStmt) syntax.Stmt {
// Set next to break the appropriate number of times;
// the final time may be a continue, not a break.
next = 2 * depth
next = perLoopStep * depth
if x.Tok == syntax.Continue {
next--
}
@ -948,10 +955,10 @@ func (r *rewriter) checks(loop *forLoop, pos syntax.Pos) []syntax.Stmt {
list = append(list, r.ifNext(syntax.Lss, 0, retStmt(r.useVar(r.false))))
}
if loop.checkBreak {
list = append(list, r.ifNext(syntax.Geq, 2, retStmt(r.useVar(r.false))))
list = append(list, r.ifNext(syntax.Geq, perLoopStep, retStmt(r.useVar(r.false))))
}
if loop.checkContinue {
list = append(list, r.ifNext(syntax.Eql, 1, retStmt(r.useVar(r.true))))
list = append(list, r.ifNext(syntax.Eql, perLoopStep-1, retStmt(r.useVar(r.true))))
}
}