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cmd/compile: try harder to not use an empty src.XPos for a bogus line
The fix for #35652 did not guarantee that it was using a non-empty src position to replace an empty one. The new code checks again and falls back to a more certain position. (The input in question compiles to a single empty infinite loop, and none of the actual instructions had any source position at all. That is a bug, but given the pathology of this input, not one worth dealing with this late in the release cycle, if ever.) Literally: 00000 (5) TEXT "".f(SB), ABIInternal 00001 (5) PCDATA $0, $-2 00002 (5) PCDATA $1, $-2 00003 (5) FUNCDATA $0, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB) 00004 (5) FUNCDATA $1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB) 00005 (5) FUNCDATA $2, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB) b2 00006 (?) XCHGL AX, AX b6 00007 (+1048575) JMP 6 00008 (?) END TODO: Add runtime.InfiniteLoop(), replace infinite loops with a call to that, and use an eco-friendly runtime.gopark instead. (This was Cherry's excellent idea.) Updates #35652 Fixes #35695 Change-Id: I4b9a841142ee4df0f6b10863cfa0721a7e13b437 Reviewed-on: https://go-review.googlesource.com/c/go/+/207964 Run-TryBot: David Chase <drchase@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Cherry Zhang <cherryyz@google.com>
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@ -6043,6 +6043,9 @@ func genssa(f *ssa.Func, pp *Progs) {
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p.Pos = p.Pos.WithIsStmt()
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if b.Pos == src.NoXPos {
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b.Pos = p.Pos // It needs a file, otherwise a no-file non-zero line causes confusion. See #35652.
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if b.Pos == src.NoXPos {
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b.Pos = pp.Text.Pos // Sometimes p.Pos is empty. See #35695.
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}
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}
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b.Pos = b.Pos.WithBogusLine() // Debuggers are not good about infinite loops, force a change in line number
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}
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@ -6,10 +6,23 @@
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package p
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func f() {
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func e() {
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for true {
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if true {
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continue
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}
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}
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}
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func g() {}
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func f() {
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i := 0
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if true {
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i++
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}
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for true {
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continue
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g()
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}
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}
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