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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - ThinLTO doesn't apply interprocedural FunctionAttrs optimization"
href="https://bugs.llvm.org/show_bug.cgi?id=33648">33648</a>
</td>
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<tr>
<th>Summary</th>
<td>ThinLTO doesn't apply interprocedural FunctionAttrs optimization
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Interprocedural Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>charles.saternos@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>LTO will apply the funcitonattrs pass, but ThinLTO can't apply this
optimization right now.
$ cat a.cc
#include <stdio.h>
#include <assert.h>
int some_global = 100;
const int garr[] = {1,2,3};
int garr2[] = {1,2,3};
__attribute__((noinline))
int a() {
return 10;
}
__attribute__((noinline))
void b(const int **x) {
printf("%p", x[0]);
}
__attribute__((noinline))
const int *c(const int *x) { // alias
return &some_global;
}
__attribute__((noinline))
int *d(int **x) { // alias, readonly arg
return x[0];
}
$ cat b.cc
#include <stdio.h>
extern int a();
extern void b(const int **x);
extern const int *c(const int *x);
extern int *d(int **x);
int main(void) {
const int arr2[] = {1,2};
int x = 3;
int y = 4;
int *arr[] = {&x, &y};
printf("%d\n", a());
b((const int **) arr);
printf("%p\n", c(&x));
printf("%p\n", d(arr));
}
$ ../build/bin/clang++ a.cc b.cc -O3 --for-linker=-mllvm --for-linker=-stats
-flto=thin -fuse-ld=lld -o thin &>&1 | grep funcitonattrs
# nothing
$ ../build/bin/clang++ a.cc b.cc -O3 --for-linker=-mllvm --for-linker=-stats
-flto -fuse-ld=lld -o lto &>&1 | grep funcitonattrs</pre>
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