Enhance ComputeMaskedBits to know that aligned frameindexes

have their low bits set to zero.  This allows us to optimize
out explicit stack alignment code like in stack-align.ll:test4 when
it is redundant.

Doing this causes the code generator to start turning FI+cst into
FI|cst all over the place, which is general goodness (that is the
canonical form) except that various pieces of the code generator
don't handle OR aggressively.  Fix this by introducing a new
SelectionDAG::isBaseWithConstantOffset predicate, and using it
in places that are looking for ADD(X,CST).  The ARM backend in
particular was missing a lot of addressing mode folding opportunities
around OR.

llvm-svn: 125470

1 files changed, 1 insertions, 2 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 596f010ec12..d5b4a1eb910 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -4201,8 +4201,7 @@ X86TargetLowering::LowerAsSplatVectorLoad(SDValue SrcOp, EVT VT, DebugLoc dl,
     if (FrameIndexSDNode *FINode = dyn_cast<FrameIndexSDNode>(Ptr)) {
       FI = FINode->getIndex();
       Offset = 0;
-    } else if (Ptr.getOpcode() == ISD::ADD &&
-               isa<ConstantSDNode>(Ptr.getOperand(1)) &&
+    } else if (DAG.isBaseWithConstantOffset(Ptr) &&
                isa<FrameIndexSDNode>(Ptr.getOperand(0))) {
       FI = cast<FrameIndexSDNode>(Ptr.getOperand(0))->getIndex();
       Offset = Ptr.getConstantOperandVal(1);