[PATCH] Optimize memcmp(x, y, n)==0 for small n and suitably aligned x/y.

[David Majnemer]

================
Comment at: lib/Transforms/Utils/SimplifyLibCalls.cpp:955
@@ +954,3 @@
+  // (And same for 16/32 bit.)
+  if (Len <= 8 && !(Len & (Len-1))
+      && isOnlyUsedInZeroEqualityComparison(CI)
----------------
Isn't the RHS just `isPowerOf2_64`?

Also, '8' sounds awfully target specific.  I doubt this is the correct number for the MSP430 target.

================
Comment at: lib/Transforms/Utils/SimplifyLibCalls.cpp:956-958
@@ +955,5 @@
+  if (Len <= 8 && !(Len & (Len-1))
+      && isOnlyUsedInZeroEqualityComparison(CI)
+      && getKnownAlignment(LHS, DL, nullptr, CI) >= Len
+      && getKnownAlignment(RHS, DL, nullptr, CI) >= Len) {
+
----------------
This seems strangely formatted, consider running clang-format over these lines.

================
Comment at: lib/Transforms/Utils/SimplifyLibCalls.cpp:960
@@ +959,3 @@
+
+    if (Type *IntType = IntegerType::get(CI->getContext(), Len << 3)) {
+
----------------
There is no need to manually strength-reduce multiplication by eight.  Also, this can never fail.

================
Comment at: lib/Transforms/Utils/SimplifyLibCalls.cpp:962-965
@@ +961,6 @@
+
+      Type *LHSPtrTy = PointerType::get(IntType,
+        cast<PointerType>(LHS->getType())->getAddressSpace());
+      Type *RHSPtrTy = PointerType::get(IntType,
+        cast<PointerType>(RHS->getType())->getAddressSpace());
+
----------------
Perhaps:
  Type *LHSPtrTy =
      IntType->getPointerTo(LHS->getType()->getPointerAddressSpace());
  Type *RHSPtrTy =
      IntType->getPointerTo(RHS->getType()->getPointerAddressSpace());

http://reviews.llvm.org/D6952

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