[SystemZ] Reclassify f32 subregs of f64 registers

At the moment, all subregs defined by the SystemZ target can be modified
independently of the wider register.  E.g. writing to a GR32 does not
change the upper 32 bits of the GR64.  Writing to an FP32 does not change
the lower 32 bits of the FP64.

Hoewver, the upcoming support for the vector extension redefines FP64 as
one half of a V128.  Floating-point operations leave the other half of
a V128 in an unpredictable state, so it's no longer the case that writing
to an FP32 leaves the bits of the underlying register (the V128) alone.
I'd prefer to have separate subreg_ names for this situation, so that
it's obvious at a glance whether we're talking about a subreg that leaves
the other parts of the register alone.

No behavioral change intended.

Patch originally by Richard Sandiford.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236433 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/SystemZ/SystemZISelLowering.cpp

@@ -2159,12 +2159,12 @@ SDValue SystemZTargetLowering::lowerBITCAST(SDValue Op,
                          DAG.getConstant(32, DL, MVT::i64));
     }
     SDValue Out64 = DAG.getNode(ISD::BITCAST, DL, MVT::f64, In64);
-    return DAG.getTargetExtractSubreg(SystemZ::subreg_h32,
+    return DAG.getTargetExtractSubreg(SystemZ::subreg_r32,
                                       DL, MVT::f32, Out64);
   }
   if (InVT == MVT::f32 && ResVT == MVT::i32) {
     SDNode *U64 = DAG.getMachineNode(TargetOpcode::IMPLICIT_DEF, DL, MVT::f64);
-    SDValue In64 = DAG.getTargetInsertSubreg(SystemZ::subreg_h32, DL,
+    SDValue In64 = DAG.getTargetInsertSubreg(SystemZ::subreg_r32, DL,
                                              MVT::f64, SDValue(U64, 0), In);
     SDValue Out64 = DAG.getNode(ISD::BITCAST, DL, MVT::i64, In64);
     if (Subtarget.hasHighWord())

lib/Target/SystemZ/SystemZInstrFP.td

@@ -141,7 +141,7 @@ def LDXBRA : UnaryRRF4<"ldxbra", 0xB345, FP128, FP128>,
              Requires<[FeatureFPExtension]>;
 
 def : Pat<(f32 (fround FP128:$src)),
-          (EXTRACT_SUBREG (LEXBR FP128:$src), subreg_hh32)>;
+          (EXTRACT_SUBREG (LEXBR FP128:$src), subreg_hr32)>;
 def : Pat<(f64 (fround FP128:$src)),
           (EXTRACT_SUBREG (LDXBR FP128:$src), subreg_h64)>;
 
@@ -345,13 +345,13 @@ def MDB  : BinaryRXE<"mdb",  0xED1C, fmul, FP64, load, 8>;
 def MDEBR : BinaryRRE<"mdeb", 0xB30C, null_frag, FP64, FP32>;
 def : Pat<(fmul (f64 (fextend FP32:$src1)), (f64 (fextend FP32:$src2))),
           (MDEBR (INSERT_SUBREG (f64 (IMPLICIT_DEF)),
-                                FP32:$src1, subreg_h32), FP32:$src2)>;
+                                FP32:$src1, subreg_r32), FP32:$src2)>;
 
 // f64 multiplication of an FP32 register and an f32 memory.
 def MDEB : BinaryRXE<"mdeb", 0xED0C, null_frag, FP64, load, 4>;
 def : Pat<(fmul (f64 (fextend FP32:$src1)),
                 (f64 (extloadf32 bdxaddr12only:$addr))),
-          (MDEB (INSERT_SUBREG (f64 (IMPLICIT_DEF)), FP32:$src1, subreg_h32),
+          (MDEB (INSERT_SUBREG (f64 (IMPLICIT_DEF)), FP32:$src1, subreg_r32),
                 bdxaddr12only:$addr)>;
 
 // f128 multiplication of two FP64 registers.

lib/Target/SystemZ/SystemZRegisterInfo.td

@@ -25,8 +25,10 @@ def subreg_l32   : SubRegIndex<32, 0>;  // Also acts as subreg_ll32.
 def subreg_h32   : SubRegIndex<32, 32>; // Also acts as subreg_lh32.
 def subreg_l64   : SubRegIndex<64, 0>;
 def subreg_h64   : SubRegIndex<64, 64>;
+def subreg_r32   : SubRegIndex<32, 32>; // Reinterpret a wider reg as 32 bits.
 def subreg_hh32  : ComposedSubRegIndex<subreg_h64, subreg_h32>;
 def subreg_hl32  : ComposedSubRegIndex<subreg_h64, subreg_l32>;
+def subreg_hr32  : ComposedSubRegIndex<subreg_h64, subreg_r32>;
 }
 
 // Define a register class that contains values of type TYPE and an
@@ -151,7 +153,7 @@ class FPR32<bits<16> num, string n> : SystemZReg<n> {
 class FPR64<bits<16> num, string n, FPR32 low>
  : SystemZRegWithSubregs<n, [low]> {
   let HWEncoding = num;
-  let SubRegIndices = [subreg_h32];
+  let SubRegIndices = [subreg_r32];
 }
 
 // 8 pairs of FPR64s, with a one-register gap inbetween.