[llvm] r192302 - Fix a bug in Dead Argument Elimination.
Shuxin Yang
shuxin.llvm at gmail.com
Wed Oct 9 10:21:44 PDT 2013
Author: shuxin_yang
Date: Wed Oct 9 12:21:44 2013
New Revision: 192302
URL: http://llvm.org/viewvc/llvm-project?rev=192302&view=rev
Log:
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
Added:
llvm/trunk/test/Transforms/DeadArgElim/linkage.ll
Modified:
llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp
Modified: llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp?rev=192302&r1=192301&r2=192302&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/DeadArgumentElimination.cpp Wed Oct 9 12:21:44 2013
@@ -357,6 +357,19 @@ bool DAE::RemoveDeadArgumentsFromCallers
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;
Added: llvm/trunk/test/Transforms/DeadArgElim/linkage.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/DeadArgElim/linkage.ll?rev=192302&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/DeadArgElim/linkage.ll (added)
+++ llvm/trunk/test/Transforms/DeadArgElim/linkage.ll Wed Oct 9 12:21:44 2013
@@ -0,0 +1,21 @@
+; RUN: opt < %s -deadargelim -S | FileCheck %s
+
+; rdar://11546243
+%struct.A = type { i8 }
+
+define available_externally void @_Z17externallyDefinedP1A(%struct.A* %a) {
+entry:
+ call void @_Z3foov()
+ ret void
+}
+
+declare void @_Z3foov()
+
+define void @_Z4testP1A(%struct.A* %a) {
+; CHECK: @_Z4testP1A
+; CHECK: @_Z17externallyDefinedP1A(%struct.A* %a)
+
+entry:
+ call void @_Z17externallyDefinedP1A(%struct.A* %a)
+ ret void
+}
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