* tree-ssa-strlen vs. zero-length strings
@ 2011-10-27 8:40 Ian Lance Taylor
0 siblings, 0 replies; only message in thread
From: Ian Lance Taylor @ 2011-10-27 8:40 UTC (permalink / raw)
To: jakub; +Cc: gcc
The file tree-ssa-strlen.c causes several warnings when compiling the Go
library. The warnings look like:
../../../gccgo2/libgo/go/http/transport.go: In function ‘http.String.pN29_libgo_http.http.connectMethod’:
../../../gccgo2/libgo/go/http/transport.go:437:1: warning: offset outside bounds of constant string [enabled by default]
They are occurring because Go uses strings which are not null
terminated. Some of those strings are zero length. The code in
tree-ssa-srlen in strlen_enter_block calls get_stridx on the PHI
arguments. get_stridx calls c_strlen. c_strlen issues the above
warning.
I don't think it is possible to trigger this using C because I don't
think it is possible to have a zero-length STRING_CST in C.
Here is a Go file which will trigger the warning when compiling with
-O2.
package p
func A(b bool) string {
s := ""
if b {
s = "a"
}
return s
}
foo.go: In function ‘p.A’:
foo.go:2:1: warning: offset outside bounds of constant string [enabled by default]
I'm not quite sure what get_stridx is doing here. Perhaps the fix is as
simple as checking TREE_STRING_LENGTH before calling c_strlen.
Ian
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2011-10-27 8:40 tree-ssa-strlen vs. zero-length strings Ian Lance Taylor
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