Fix a bug in Dead Argument Elimination.
If a function seen at compile time is not necessarily the one linked to
the binary being built, it is illegal to change the actual arguments
passing to it.
e.g.
--------------------------
void foo(int lol) {
// foo() has linkage satisifying isWeakForLinker()
// "lol" is not used at all.
}
void bar(int lo2) {
// xform to foo(undef) is illegal, as compiler dose not know which
// instance of foo() will be linked to the the binary being built.
foo(lol2);
}
-----------------------------
Such functions can be captured by isWeakForLinker(). NOTE that
mayBeOverridden() is insufficient for this purpose as it dosen't include
linkage types like AvailableExternallyLinkage and LinkOnceODRLinkage.
Take link_odr* as an example, it indicates a set of *EQUIVALENT* globals
that can be merged at link-time. However, the semantic of
*EQUIVALENT*-functions includes parameters. Changing parameters breaks
the assumption.
Thank John McCall for help, especially for the explanation of subtle
difference between linkage types.
rdar://11546243
llvm-svn: 192302
diff --git a/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp b/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
index 6ee6162..8621f1a 100644
--- a/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
+++ b/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
@@ -357,6 +357,19 @@
if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg())
return false;
+ // If a function seen at compile time is not necessarily the one linked to
+ // the binary being built, it is illegal to change the actual arguments
+ // passing to it. These functions can be captured by isWeakForLinker().
+ // *NOTE* that mayBeOverridden() is insufficient for this purpose as it
+ // dosen't include linkage types like AvailableExternallyLinkage and
+ // LinkOnceODRLinkage. Take link_odr* as an example, it indicates a set of
+ // *EQUIVALENT* globals that can be merged at link-time. However, the
+ // semantic of *EQUIVALENT*-functions includes parameters. Changing
+ // parameters breaks the assumption.
+ //
+ if (Fn.isWeakForLinker())
+ return false;
+
if (Fn.use_empty())
return false;