[X86] Teach 'getTargetShuffleMask' how to look through ISD::WrapperRIP when decoding a PSHUFB mask.

The function 'getTargetShuffleMask' already knows how to deal with PSHUFB nodes
where the mask node is a load from constant pool, and the constant pool node
is wrapped by a X86ISD::Wrapper node. This patch extends that logic by teaching
it how to also look through X86ISD::WrapperRIP.

This helps function combineX86ShufflesRecusively to combine more shuffle
sequences containing PSHUFB nodes if we are in RIPRel PIC mode.

Before this change, llc (with -relocation-model=pic -march=x86-64) was unable
to decode a pshufb where the mask was loaded from a constant pool. For example,
the no-op shuffle from test 'x86-fold-pshufb.ll' was not folded into its
operand, so instead of generating a single 'movaps' the backend always
generated a sub-optimal 'movdqa + pshufb' sequence.

Added test x86-fold-pshufb.ll.

llvm-svn: 236863

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index cac5b54187b..35517212acc 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -4352,7 +4352,8 @@ static bool getTargetShuffleMask(SDNode *N, MVT VT,
       return false;
 
     SDValue Ptr = MaskLoad->getBasePtr();
-    if (Ptr->getOpcode() == X86ISD::Wrapper)
+    if (Ptr->getOpcode() == X86ISD::Wrapper ||
+        Ptr->getOpcode() == X86ISD::WrapperRIP)
       Ptr = Ptr->getOperand(0);
 
     auto *MaskCP = dyn_cast<ConstantPoolSDNode>(Ptr);