[clang] [analyzer] Check the correct first and last elements in cstring.UninitializedRead (PR #95408)

[Donát Nagy via cfe-commits]

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@@ -26,16 +50,12 @@ void top(char *dst) {
 
 void *mempcpy(void *restrict s1, const void *restrict s2, size_t n);
 
-void mempcpy14() {
+void mempcpy13() {
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NagyDonat wrote:

Why are you renaming this to `memcpy13`? I see only two `memcpy` tests after this and they have index 15 and 16, which is very random, but at least follows 14 directly.

https://github.com/llvm/llvm-project/pull/95408