[PowerPC] Use true offset value in "memrix" machine operands

This is the second part of the change to always return "true"
offset values from getPreIndexedAddressParts, tackling the
case of "memrix" type operands.

This is about instructions like LD/STD that only have a 14-bit
field to encode immediate offsets, which are implicitly extended
by two zero bits by the machine, so that in effect we can access
16-bit offsets as long as they are a multiple of 4.

The PowerPC back end currently handles such instructions by
carrying the 14-bit value (as it will get encoded into the
actual machine instructions) in the machine operand fields
for such instructions.  This means that those values are
in fact not the true offset, but rather the offset divided
by 4 (and then truncated to an unsigned 14-bit value).

Like in the case fixed in r182012, this makes common code
operations on such offset values not work as expected.
Furthermore, there doesn't really appear to be any strong
reason why we should encode machine operands this way.

This patch therefore changes the encoding of "memrix" type
machine operands to simply contain the "true" offset value
as a signed immediate value, while enforcing the rules that
it must fit in a 16-bit signed value and must also be a
multiple of 4.

This change must be made simultaneously in all places that
access machine operands of this type.  However, just about
all those changes make the code simpler; in many cases we
can now just share the same code for memri and memrix
operands.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182032 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 3 insertions, 8 deletions

diff --git a/lib/Target/PowerPC/PPCISelLowering.h b/lib/Target/PowerPC/PPCISelLowering.h
index fc4314c..e21f322 100644
--- a/lib/Target/PowerPC/PPCISelLowering.h
+++ b/lib/Target/PowerPC/PPCISelLowering.h
@@ -366,21 +366,16 @@ namespace llvm {
 
     /// SelectAddressRegImm - Returns true if the address N can be represented
     /// by a base register plus a signed 16-bit displacement [r+imm], and if it
-    /// is not better represented as reg+reg.
+    /// is not better represented as reg+reg.  If Aligned is true, only accept
+    /// displacements suitable for STD and friends, i.e. multiples of 4.
     bool SelectAddressRegImm(SDValue N, SDValue &Disp, SDValue &Base,
-                             SelectionDAG &DAG) const;
+                             SelectionDAG &DAG, bool Aligned) const;
 
     /// SelectAddressRegRegOnly - Given the specified addressed, force it to be
     /// represented as an indexed [r+r] operation.
     bool SelectAddressRegRegOnly(SDValue N, SDValue &Base, SDValue &Index,
                                  SelectionDAG &DAG) const;
 
-    /// SelectAddressRegImmShift - Returns true if the address N can be
-    /// represented by a base register plus a signed 14-bit displacement
-    /// [r+imm*4].  Suitable for use by STD and friends.
-    bool SelectAddressRegImmShift(SDValue N, SDValue &Disp, SDValue &Base,
-                                  SelectionDAG &DAG) const;
-
     Sched::Preference getSchedulingPreference(SDNode *N) const;
 
     /// LowerOperation - Provide custom lowering hooks for some operations.