[llvm] r191000 - DAGCombiner: Don't fold vector muls with constants that look like a splat of a power of 2 but differ in bit width.

[Benjamin Kramer]

Author: d0k
Date: Thu Sep 19 08:28:20 2013
New Revision: 191000

URL: http://llvm.org/viewvc/llvm-project?rev=191000&view=rev
Log:
DAGCombiner: Don't fold vector muls with constants that look like a splat of a power of 2 but differ in bit width.

PR17283.

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    llvm/trunk/test/CodeGen/X86/avx2-arith.ll

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=191000&r1=190999&r2=191000&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Thu Sep 19 08:28:20 2013
@@ -1824,20 +1824,24 @@ SDValue DAGCombiner::visitMUL(SDNode *N)
   // fold (mul x, 0) -> 0
   if (N1IsConst && ConstValue1 == 0)
     return N1;
+  // We require a splat of the entire scalar bit width for non-contiguous
+  // bit patterns.
+  bool IsFullSplat =
+    ConstValue1.getBitWidth() == VT.getScalarType().getSizeInBits();
   // fold (mul x, 1) -> x
-  if (N1IsConst && ConstValue1 == 1)
+  if (N1IsConst && ConstValue1 == 1 && IsFullSplat)
     return N0;
   // fold (mul x, -1) -> 0-x
   if (N1IsConst && ConstValue1.isAllOnesValue())
     return DAG.getNode(ISD::SUB, SDLoc(N), VT,
                        DAG.getConstant(0, VT), N0);
   // fold (mul x, (1 << c)) -> x << c
-  if (N1IsConst && ConstValue1.isPowerOf2())
+  if (N1IsConst && ConstValue1.isPowerOf2() && IsFullSplat)
     return DAG.getNode(ISD::SHL, SDLoc(N), VT, N0,
                        DAG.getConstant(ConstValue1.logBase2(),
                                        getShiftAmountTy(N0.getValueType())));
   // fold (mul x, -(1 << c)) -> -(x << c) or (-x) << c
-  if (N1IsConst && (-ConstValue1).isPowerOf2()) {
+  if (N1IsConst && (-ConstValue1).isPowerOf2() && IsFullSplat) {
     unsigned Log2Val = (-ConstValue1).logBase2();
     // FIXME: If the input is something that is easily negated (e.g. a
     // single-use add), we should put the negate there.

Modified: llvm/trunk/test/CodeGen/X86/avx2-arith.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/avx2-arith.ll?rev=191000&r1=190999&r2=191000&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/avx2-arith.ll (original)
+++ llvm/trunk/test/CodeGen/X86/avx2-arith.ll Thu Sep 19 08:28:20 2013
@@ -148,3 +148,21 @@ define <8 x i32> @mul_const9(<8 x i32> %
   %y = mul <8 x i32> %x, <i32 2, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0>
   ret <8 x i32> %y
 }
+
+; CHECK: mul_const10
+; CHECK: vpmulld
+; CHECK: ret
+define <4 x i32> @mul_const10(<4 x i32> %x) {
+  ; %x * 0x01010101
+  %m = mul <4 x i32> %x, <i32 16843009, i32 16843009, i32 16843009, i32 16843009>
+  ret <4 x i32> %m
+}
+
+; CHECK: mul_const11
+; CHECK: vpmulld
+; CHECK: ret
+define <4 x i32> @mul_const11(<4 x i32> %x) {
+  ; %x * 0x80808080
+  %m = mul <4 x i32> %x, <i32 2155905152, i32 2155905152, i32 2155905152, i32 2155905152>
+  ret <4 x i32> %m
+}