Add a comment about using libc memset/memcpy or generating inline code.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@41502 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 75fbd44..2e9dce3 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -3754,7 +3754,8 @@
ConstantSDNode *I = dyn_cast<ConstantSDNode>(Op.getOperand(3));
// If not DWORD aligned or size is more than the threshold, call memset.
- // It knows how to align to the right boundary first.
+ // The libc version is likely to be faster for these cases. It can use the
+ // address value and run time information about the CPU.
if ((Align & 3) != 0 ||
(I && I->getValue() > Subtarget->getMinRepStrSizeThreshold())) {
MVT::ValueType IntPtr = getPointerTy();
@@ -3910,7 +3911,9 @@
ConstantSDNode *I = dyn_cast<ConstantSDNode>(Op.getOperand(3));
// If not DWORD aligned or size is more than the threshold, call memcpy.
- // It knows how to align to the right boundary first.
+ // The libc version is likely to be faster for these cases. It can use the
+ // address value and run time information about the CPU.
+ // With glibc 2.6.1 on a core 2, coping an array of 100M longs was 30% faster
if ((Align & 3) != 0 ||
(I && I->getValue() > Subtarget->getMinRepStrSizeThreshold())) {
MVT::ValueType IntPtr = getPointerTy();