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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 all interprocedural GlobalOptimzation optimizations"
href="https://bugs.llvm.org/show_bug.cgi?id=33657">33657</a>
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<th>Summary</th>
<td>ThinLTO doesn't apply all interprocedural GlobalOptimzation optimizations
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Interprocedural Optimizations
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>charles.saternos@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<pre>LTO will apply the globalopt pass, but ThinLTO can't apply all these
optimizations right now.
$ cat a.cc
#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
char x = 0; // shrunk to bool
char b = 1; // localized
bool c = false; // deleted
int p[] = {1, 2, 3}; // scalarized
void bb() {
if(rand() % 8) {
x = 1;
}
}
int jj() {
b = (rand() % 2);
return b == 0;
}
$ cat b.cc
#include <stdio.h>
#include <stdlib.h>
extern char x;
extern bool c;
extern int p[];
extern int jj();
extern void bb();
void cc() {
if(rand() % 8) {
x = 1;
}
}
int main(void) {
printf("%d\n", p[1]++);
bb();
cc();
if(x) {
puts("Hi");
}
for(int i = 0; i < 200; i++) {
printf("%d\n", jj());
}
if(c)
puts("yo");
}
$ ../build/bin/clang++ a.cc b.cc -O3 --for-linker=-mllvm --for-linker=-stats
-flto=thin -fuse-ld=lld -o thin &>&1 | grep globalopt
1 globalopt - Number of globals deleted
$ ../build/bin/clang++ a.cc b.cc -O3 --for-linker=-mllvm --for-linker=-stats
-flto -fuse-ld=lld -o lto &>&1 | grep globalopt
1 globalopt - Number of globals deleted
2 globalopt - Number of functions converted to fastcc
1 globalopt - Number of globals localized
1 globalopt - Number of aggregate globals broken into scalars
1 globalopt - Number of global vars shrunk to booleans
6 globalopt - Number of globals marked unnamed_addr</pre>
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