[llvm-commits] [llvm] r48057 - /llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

[Chris Lattner]

Author: lattner
Date: Sat Mar  8 16:59:52 2008
New Revision: 48057

URL: http://llvm.org/viewvc/llvm-project?rev=48057&view=rev
Log:
1) Improve comments.
2) Don't try to insert an i64 value into the low part of a 
   vector with movq on an x86-32 target.  This allows us to 
   compile:

__m128i doload64(short x) {return _mm_set_epi16(0,0,0,0,0,0,0,1);}

into:

_doload64:
	movaps	LCPI1_0, %xmm0
	ret

instead of:

_doload64:
	subl	$28, %esp
	movl	$0, 4(%esp)
	movl	$1, (%esp)
	movq	(%esp), %xmm0
	addl	$28, %esp
	ret

Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=48057&r1=48056&r2=48057&view=diff

==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Sat Mar  8 16:59:52 2008
@@ -3055,7 +3055,15 @@
   if (NumNonZero == 1 && NumElems <= 4) {
     unsigned Idx = CountTrailingZeros_32(NonZeros);
     SDOperand Item = Op.getOperand(Idx);
-    if (Idx == 0) {
+    
+    // If we have a constant or non-constant insertion into the low element of
+    // a vector, we can do this with SCALAR_TO_VECTOR + shuffle of zero into
+    // the rest of the elements.  This will be matched as movd/movq/movss/movsd
+    // depending on what the source datatype is.  Because we can only get here
+    // when NumElems <= 4, this only needs to handle i32/f32/i64/f64.
+    if (Idx == 0 &&
+        // Don't do this for i64 values on x86-32.
+        (EVT != MVT::i64 || Subtarget->is64Bit())) {
       Item = DAG.getNode(ISD::SCALAR_TO_VECTOR, VT, Item);
       // Turn it into a MOVL (i.e. movss, movsd, or movd) to a zero vector.
       return getShuffleVectorZeroOrUndef(Item, VT, NumElems, Idx,
@@ -3065,6 +3073,11 @@
     if (IsAllConstants) // Otherwise, it's better to do a constpool load.
       return SDOperand();
 
+    // Otherwise, if this is a vector with i32 or f32 elements, and the element
+    // is a non-constant being inserted into an element other than the low one,
+    // we can't use a constant pool load.  Instead, use SCALAR_TO_VECTOR (aka
+    // movd/movss) to move this into the low element, then shuffle it into
+    // place.
     if (EVTBits == 32) {
       Item = DAG.getNode(ISD::SCALAR_TO_VECTOR, VT, Item);