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Diffstat (limited to 'docs/LinkTimeOptimization.html')
| -rw-r--r-- | docs/LinkTimeOptimization.html | 59 |
1 files changed, 33 insertions, 26 deletions
diff --git a/docs/LinkTimeOptimization.html b/docs/LinkTimeOptimization.html index 289da236270a..a1e8bba74d05 100644 --- a/docs/LinkTimeOptimization.html +++ b/docs/LinkTimeOptimization.html @@ -79,7 +79,7 @@ conservative escape analysis. <p>The following example illustrates the advantages of LTO's integrated approach and clean interface. This example requires a system linker which supports LTO through the interface described in this document. Here, - llvm-gcc transparently invokes system linker. </p> + clang transparently invokes system linker. </p> <ul> <li> Input source file <tt>a.c</tt> is compiled into LLVM bitcode form. <li> Input source file <tt>main.c</tt> is compiled into native object code. @@ -89,27 +89,29 @@ conservative escape analysis. extern int foo1(void); extern void foo2(void); extern void foo4(void); + --- a.c --- #include "a.h" static signed int i = 0; void foo2(void) { - i = -1; + i = -1; } static int foo3() { -foo4(); -return 10; + foo4(); + return 10; } int foo1(void) { -int data = 0; + int data = 0; -if (i < 0) { data = foo3(); } + if (i < 0) + data = foo3(); -data = data + 42; -return data; + data = data + 42; + return data; } --- main.c --- @@ -117,30 +119,35 @@ return data; #include "a.h" void foo4(void) { - printf ("Hi\n"); + printf("Hi\n"); } int main() { - return foo1(); + return foo1(); } --- command lines --- -$ llvm-gcc --emit-llvm -c a.c -o a.o # <-- a.o is LLVM bitcode file -$ llvm-gcc -c main.c -o main.o # <-- main.o is native object file -$ llvm-gcc a.o main.o -o main # <-- standard link command without any modifications +$ clang -emit-llvm -c a.c -o a.o # <-- a.o is LLVM bitcode file +$ clang -c main.c -o main.o # <-- main.o is native object file +$ clang a.o main.o -o main # <-- standard link command without any modifications </pre> - <p>In this example, the linker recognizes that <tt>foo2()</tt> is an - externally visible symbol defined in LLVM bitcode file. The linker completes - its usual symbol resolution - pass and finds that <tt>foo2()</tt> is not used anywhere. This information - is used by the LLVM optimizer and it removes <tt>foo2()</tt>. As soon as - <tt>foo2()</tt> is removed, the optimizer recognizes that condition - <tt>i < 0</tt> is always false, which means <tt>foo3()</tt> is never - used. Hence, the optimizer removes <tt>foo3()</tt>, also. And this in turn, - enables linker to remove <tt>foo4()</tt>. This example illustrates the - advantage of tight integration with the linker. Here, the optimizer can not - remove <tt>foo3()</tt> without the linker's input. - </p> + +<ul> + <li>In this example, the linker recognizes that <tt>foo2()</tt> is an + externally visible symbol defined in LLVM bitcode file. The linker + completes its usual symbol resolution pass and finds that <tt>foo2()</tt> + is not used anywhere. This information is used by the LLVM optimizer and + it removes <tt>foo2()</tt>.</li> + <li>As soon as <tt>foo2()</tt> is removed, the optimizer recognizes that condition + <tt>i < 0</tt> is always false, which means <tt>foo3()</tt> is never + used. Hence, the optimizer also removes <tt>foo3()</tt>.</li> + <li>And this in turn, enables linker to remove <tt>foo4()</tt>.</li> +</ul> + +<p>This example illustrates the advantage of tight integration with the + linker. Here, the optimizer can not remove <tt>foo3()</tt> without the + linker's input.</p> + </div> <!-- ======================================================================= --> @@ -385,7 +392,7 @@ of the native object files.</p> Devang Patel and Nick Kledzik<br> <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br> - Last modified: $Date: 2011-04-23 02:30:22 +0200 (Sat, 23 Apr 2011) $ + Last modified: $Date: 2011-09-18 14:51:05 +0200 (Sun, 18 Sep 2011) $ </address> </body> |