[llvm-commits] [patch] call libc memcpy/memset for big arrays

[Rafael Espindola]

Currently we expand a memcpy/memset node to a call to the libc implementation if

  if ((Align & 3) != 0 ||
      (I && I->getValue() < Subtarget->getMinRepStrSizeThreshold())) {

Shouldn't this be a ">". The libc memcpy/memset are very fast for big arrays.

If I compile

---------------------------------------
#include <string.h>
void f1(long *a, long *b) {
  memcpy(a, b, 8 * 16);
}

void f2(long *a, long *b) {
  memcpy(a, b, 8 * 32);
}
---------------------------------------

with gcc 4.2 (-O2), it will call memcpy for f2 and not for f1.

Cheers,
-- 
Rafael Avila de Espindola

Google Ireland Ltd.
Gordon House
Barrow Street
Dublin 4
Ireland

Registered in Dublin, Ireland
Registration Number: 368047

Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp	(revision 41327)
+++ lib/Target/X86/X86ISelLowering.cpp	(working copy)
@@ -3753,10 +3753,10 @@
   if (Align == 0) Align = 1;
 
   ConstantSDNode *I = dyn_cast<ConstantSDNode>(Op.getOperand(3));
-  // If not DWORD aligned, call memset if size is less than the threshold.
+  // If not DWORD aligned or size is more than the threshold, call memset.
   // It knows how to align to the right boundary first.
   if ((Align & 3) != 0 ||
-      (I && I->getValue() < Subtarget->getMinRepStrSizeThreshold())) {
+      (I && I->getValue() > Subtarget->getMinRepStrSizeThreshold())) {
     MVT::ValueType IntPtr = getPointerTy();
     const Type *IntPtrTy = getTargetData()->getIntPtrType();
     TargetLowering::ArgListTy Args; 
@@ -3909,10 +3909,10 @@
   if (Align == 0) Align = 1;
 
   ConstantSDNode *I = dyn_cast<ConstantSDNode>(Op.getOperand(3));
-  // If not DWORD aligned, call memcpy if size is less than the threshold.
+  // If not DWORD aligned or size is more than the threshold, call memcpy.
   // It knows how to align to the right boundary first.
   if ((Align & 3) != 0 ||
-      (I && I->getValue() < Subtarget->getMinRepStrSizeThreshold())) {
+      (I && I->getValue() > Subtarget->getMinRepStrSizeThreshold())) {
     MVT::ValueType IntPtr = getPointerTy();
     TargetLowering::ArgListTy Args;
     TargetLowering::ArgListEntry Entry;

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