From 36597a5ddb11d9f84638a8e1e8cfa28292eeced0 Mon Sep 17 00:00:00 2001
From: Chris Lattner
Date: Wed, 12 Sep 2007 17:53:10 +0000
Subject: Change llvm.gcroot to not init the root to null at runtime, this
prevents using it for live-in values etc.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@41879 91177308-0d34-0410-b5e6-96231b3b80d8
---
docs/GarbageCollection.html | 7 ++++---
lib/Transforms/Scalar/LowerGC.cpp | 5 +----
2 files changed, 5 insertions(+), 7 deletions(-)
diff --git a/docs/GarbageCollection.html b/docs/GarbageCollection.html
index 0accd0c78a..e39e85ce3c 100644
--- a/docs/GarbageCollection.html
+++ b/docs/GarbageCollection.html
@@ -166,9 +166,7 @@ interface that front-end authors should generate code for.
The llvm.gcroot 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 must be a constant or global value address). At
-runtime, the llvm.gcroot intrinsic stores a null pointer into the
-specified location to initialize the pointer.
+with the pointer (which must be a constant or global value address).
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:
diff --git a/lib/Transforms/Scalar/LowerGC.cpp b/lib/Transforms/Scalar/LowerGC.cpp
index 98070995af..bac7ac799b 100644
--- a/lib/Transforms/Scalar/LowerGC.cpp
+++ b/lib/Transforms/Scalar/LowerGC.cpp
@@ -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]);
}
--
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