Add TRI::getSubRegIndexLaneMask().

Sub-register lane masks are bitmasks that can be used to determine if
two sub-registers of a virtual register will overlap. For example, ARM's
ssub0 and ssub1 sub-register indices don't overlap each other, but both
overlap dsub0 and qsub0.

The lane masks will be accurate on most targets, but on targets that use
sub-register indexes in an irregular way, the masks may conservatively
report that two sub-register indices overlap when the eventually
allocated physregs don't.

Irregular register banks also mean that the bits in a lane mask can't be
mapped onto register units, but the concept is similar.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163630 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 30 insertions, 1 deletions

diff --git a/include/llvm/Target/TargetRegisterInfo.h b/include/llvm/Target/TargetRegisterInfo.h
index d6d5409835..942ee44827 100644
--- a/include/llvm/Target/TargetRegisterInfo.h
+++ b/include/llvm/Target/TargetRegisterInfo.h
@@ -221,13 +221,17 @@ public:
 private:
   const TargetRegisterInfoDesc *InfoDesc;     // Extra desc array for codegen
   const char *const *SubRegIndexNames;        // Names of subreg indexes.
+  // Pointer to array of lane masks, one per sub-reg index.
+  const unsigned *SubRegIndexLaneMasks;
+
   regclass_iterator RegClassBegin, RegClassEnd;   // List of regclasses
 
 protected:
   TargetRegisterInfo(const TargetRegisterInfoDesc *ID,
                      regclass_iterator RegClassBegin,
                      regclass_iterator RegClassEnd,
-                     const char *const *subregindexnames);
+                     const char *const *SRINames,
+                     const unsigned *SRILaneMasks);
   virtual ~TargetRegisterInfo();
 public:
 
@@ -332,6 +336,31 @@ public:
     return SubRegIndexNames[SubIdx-1];
   }
 
+  /// getSubRegIndexLaneMask - Return a bitmask representing the parts of a
+  /// register that are covered by SubIdx.
+  ///
+  /// Lane masks for sub-register indices are similar to register units for
+  /// physical registers. The individual bits in a lane mask can't be assigned
+  /// any specific meaning. They can be used to check if two sub-register
+  /// indices overlap.
+  ///
+  /// If the target has a register such that:
+  ///
+  ///   getSubReg(Reg, A) overlaps getSubReg(Reg, B)
+  ///
+  /// then:
+  ///
+  ///   getSubRegIndexLaneMask(A) & getSubRegIndexLaneMask(B) != 0
+  ///
+  /// The converse is not necessarily true. If two lane masks have a common
+  /// bit, the corresponding sub-registers may not overlap, but it can be
+  /// assumed that they usually will.
+  unsigned getSubRegIndexLaneMask(unsigned SubIdx) const {
+    // SubIdx == 0 is allowed, it has the lane mask ~0u.
+    assert(SubIdx < getNumSubRegIndices() && "This is not a subregister index");
+    return SubRegIndexLaneMasks[SubIdx];
+  }
+
   /// regsOverlap - Returns true if the two registers are equal or alias each
   /// other. The registers may be virtual register.
   bool regsOverlap(unsigned regA, unsigned regB) const {