Update llvm/clang to trunk r126547.

There are several bugfixes in this update, but the most important one is
to ensure __start_ and __stop_ symbols for linker sets and kernel module
metadata are always emitted in object files:

  http://llvm.org/bugs/show_bug.cgi?id=9292

Before this fix, if you compiled kernel modules with clang, they would
not be properly processed by kldxref, and if they had any dependencies,
the kernel would fail to load those.  Another problem occurred when
attempting to mount a tmpfs filesystem, which would result in 'operation
not supported by device'.

1 files changed, 15 insertions, 3 deletions

diff --git a/contrib/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp b/contrib/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
index d7fa149..f8ce214 100644
--- a/contrib/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
+++ b/contrib/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
@@ -31,6 +31,11 @@
 //   void foo(_Complex float *P)
 //     for (i) { __real__(*P) = 0;  __imag__(*P) = 0; }
 //
+// We should enhance this to handle negative strides through memory.
+// Alternatively (and perhaps better) we could rely on an earlier pass to force
+// forward iteration through memory, which is generally better for cache
+// behavior.  Negative strides *do* happen for memset/memcpy loops.
+//
 // This could recognize common matrix multiplies and dot product idioms and
 // replace them with calls to BLAS (if linked in??).
 //
@@ -272,10 +277,17 @@ bool LoopIdiomRecognize::processLoopStore(StoreInst *SI, const SCEV *BECount) {
   unsigned StoreSize = (unsigned)SizeInBits >> 3; 
   const SCEVConstant *Stride = dyn_cast<SCEVConstant>(StoreEv->getOperand(1));
   
-  // TODO: Could also handle negative stride here someday, that will require the
-  // validity check in mayLoopAccessLocation to be updated though.
-  if (Stride == 0 || StoreSize != Stride->getValue()->getValue())
+  if (Stride == 0 || StoreSize != Stride->getValue()->getValue()) {
+    // TODO: Could also handle negative stride here someday, that will require
+    // the validity check in mayLoopAccessLocation to be updated though.
+    // Enable this to print exact negative strides.
+    if (0 && Stride && StoreSize == -Stride->getValue()->getValue()) {
+      dbgs() << "NEGATIVE STRIDE: " << *SI << "\n";
+      dbgs() << "BB: " << *SI->getParent();
+    }
+    
     return false;
+  }
 
   // See if we can optimize just this store in isolation.
   if (processLoopStridedStore(StorePtr, StoreSize, SI->getAlignment(),