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Change llvm.gcroot to not init the root to null at runtime, this prevents

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using it for live-in values etc.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@41879 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-09-12 17:53:10 +00:00
parent ea58310496
commit 36597a5ddb
2 changed files with 5 additions and 7 deletions
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7
docs/GarbageCollection.html
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@ -166,9 +166,7 @@ interface that front-end authors should generate code for.
The <tt>llvm.gcroot</tt> intrinsic is used to inform LLVM of a pointer variable
on the stack. The first argument contains the address of the variable on the
stack, and the second contains a pointer to metadata that should be associated
with the pointer (which <b>must</b> be a constant or global value address). At
runtime, the <tt>llvm.gcroot</tt> intrinsic stores a null pointer into the
specified location to initialize the pointer.</p>
with the pointer (which <b>must</b> be a constant or global value address).</p>
<p>
Consider the following fragment of Java code:
@ -193,6 +191,9 @@ Entry:
%X = alloca %Object*
...
;; Java null-initializes pointers.
store %Object* null, %Object** %X
;; "CodeBlock" is the block corresponding to the start
;; of the scope above.
CodeBlock:

5
lib/Transforms/Scalar/LowerGC.cpp
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@ -284,10 +284,7 @@ bool LowerGC::runOnFunction(Function &F) {
new StoreInst(Null, RootPtrPtr, IP);
// Each occurrance of the llvm.gcroot intrinsic now turns into an
// initialization of the slot with the address and a zeroing out of the
// address specified.
new StoreInst(Constant::getNullValue(PtrLocTy->getElementType()),
GCRoots[i]->getOperand(1), GCRoots[i]);
// initialization of the slot with the address.
new StoreInst(GCRoots[i]->getOperand(1), RootPtrPtr, GCRoots[i]);
}