Some enhancements for memcpy / memset inline expansion.

1. Teach it to use overlapping unaligned load / store to copy / set the trailing
   bytes. e.g. On 86, use two pairs of movups / movaps for 17 - 31 byte copies.
2. Use f64 for memcpy / memset on targets where i64 is not legal but f64 is. e.g.
   x86 and ARM.
3. When memcpy from a constant string, do *not* replace the load with a constant
   if it's not possible to materialize an integer immediate with a single
   instruction (required a new target hook: TLI.isIntImmLegal()).
4. Use unaligned load / stores more aggressively if target hooks indicates they
   are "fast".
5. Update ARM target hooks to use unaligned load / stores. e.g. vld1.8 / vst1.8.
   Also increase the threshold to something reasonable (8 for memset, 4 pairs
   for memcpy).

This significantly improves Dhrystone, up to 50% on ARM iOS devices.

rdar://12760078

llvm-svn: 169791

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 84e5677d6c1..90bee41e35d 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -1412,6 +1412,13 @@ X86TargetLowering::getOptimalMemOpType(uint64_t Size,
   return MVT::i32;
 }
 
+bool
+X86TargetLowering::allowsUnalignedMemoryAccesses(EVT VT, bool *Fast) const {
+  if (Fast)
+    *Fast = Subtarget->isUnalignedMemAccessFast();
+  return true;
+}
+
 /// getJumpTableEncoding - Return the entry encoding for a jump table in the
 /// current function.  The returned value is a member of the
 /// MachineJumpTableInfo::JTEntryKind enum.