Memory Dependence Analysis (not mem-dep test) take advantage of "invariant.load" metadata.

The "invariant.load" metadata indicates the memory unit being accessed is immutable.
A load annotated with this metadata can be moved across any store.

As I am not sure if it is legal to move such loads across barrier/fence, this
change dose not allow such transformation.

rdar://11311484

Thank Arnold for code review.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176562 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 7 insertions, 3 deletions

diff --git a/include/llvm/Analysis/MemoryDependenceAnalysis.h b/include/llvm/Analysis/MemoryDependenceAnalysis.h
index b87f886c00..47afd1b77b 100644
--- a/include/llvm/Analysis/MemoryDependenceAnalysis.h
+++ b/include/llvm/Analysis/MemoryDependenceAnalysis.h
@@ -391,14 +391,17 @@ namespace llvm {
     /// getPointerDependencyFrom - Return the instruction on which a memory
     /// location depends.  If isLoad is true, this routine ignores may-aliases
     /// with read-only operations.  If isLoad is false, this routine ignores
-    /// may-aliases with reads from read-only locations.
+    /// may-aliases with reads from read-only locations. If possible, pass
+    /// the query instruction as well; this function may take advantage of 
+    /// the metadata annotated to the query instruction to refine the result.
     ///
     /// Note that this is an uncached query, and thus may be inefficient.
     ///
     MemDepResult getPointerDependencyFrom(const AliasAnalysis::Location &Loc,
                                           bool isLoad,
                                           BasicBlock::iterator ScanIt,
-                                          BasicBlock *BB);
+                                          BasicBlock *BB,
+                                          Instruction *QueryInst = 0);
 
 
     /// getLoadLoadClobberFullWidthSize - This is a little bit of analysis that
diff --git a/include/llvm/IR/LLVMContext.h b/include/llvm/IR/LLVMContext.h
index b3c558bbcd..ae81e5b1c3 100644
--- a/include/llvm/IR/LLVMContext.h
+++ b/include/llvm/IR/LLVMContext.h
@@ -46,7 +46,8 @@ public:
     MD_prof = 2,  // "prof"
     MD_fpmath = 3,  // "fpmath"
     MD_range = 4, // "range"
-    MD_tbaa_struct = 5 // "tbaa.struct"
+    MD_tbaa_struct = 5, // "tbaa.struct"
+    MD_invariant_load = 6 // "invariant.load"
   };
   
   /// getMDKindID - Return a unique non-zero ID for the specified metadata kind.