Add support for getRegisterByName.

[sidneym]

Summary

Support required to build the Hexagon Linux kernel.
Code like this:
register int r19 asm("r19");
int foo() {

return r19;

}

[sidneym]

Hexagon only supports named register, r19.

lib/Target/Hexagon/HexagonISelLowering.h

 
     bool mayBeEmittedAsTailCall(const CallInst *CI) const override;
 
+    unsigned getRegisterByName(const char* RegName, EVT VT,
+                               SelectionDAG &DAG) const override;
+
     /// If a physical register, this returns the register that receives the
     /// exception address on entry to an EH pad.
     unsigned

lib/Target/Hexagon/HexagonISelLowering.cpp

 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringSwitch.h"
 #include "llvm/CodeGen/CallingConvLower.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"

   return true;
 }
 
+unsigned  HexagonTargetLowering::getRegisterByName(const char* RegName, EVT VT,
+                                              SelectionDAG &DAG) const {
+  unsigned Reg = StringSwitch<unsigned>(RegName)
+                     .Case("r0", Hexagon::R0)
+                     .Case("r1", Hexagon::R1)
+                     .Case("r2", Hexagon::R2)
+                     .Case("r3", Hexagon::R3)
+                     .Case("r4", Hexagon::R4)
+                     .Case("r5", Hexagon::R5)
+                     .Case("r6", Hexagon::R6)
+                     .Case("r7", Hexagon::R7)
+                     .Case("r8", Hexagon::R8)
+                     .Case("r9", Hexagon::R9)
+                     .Case("r10", Hexagon::R10)
+                     .Case("r11", Hexagon::R11)
+                     .Case("r12", Hexagon::R12)
+                     .Case("r13", Hexagon::R13)
+                     .Case("r14", Hexagon::R14)
+                     .Case("r15", Hexagon::R15)
+                     .Case("r16", Hexagon::R16)
+                     .Case("r17", Hexagon::R17)
+                     .Case("r18", Hexagon::R18)
+                     .Case("r19", Hexagon::R19)
+                     .Case("r20", Hexagon::R20)
+                     .Case("r21", Hexagon::R21)
+                     .Case("r22", Hexagon::R22)
+                     .Case("r23", Hexagon::R23)
+                     .Case("r24", Hexagon::R24)
+                     .Case("r25", Hexagon::R25)
+                     .Case("r26", Hexagon::R26)
+                     .Case("r27", Hexagon::R27)
+                     .Case("r28", Hexagon::R28)
+                     .Case("r29", Hexagon::R29)
+                     .Case("sp", Hexagon::R29)
+                     .Case("r30", Hexagon::R30)
+                     .Case("fp", Hexagon::R30)
+                     .Case("r31", Hexagon::R31)
+                     .Case("sp", Hexagon::R31)
+                     .Default(0);
+  if (Reg)
+    return Reg;
+
+  report_fatal_error("Invalid register name global variable");
+}
+
 /// LowerCallResult - Lower the result values of an ISD::CALL into the
 /// appropriate copies out of appropriate physical registers.  This assumes that
 /// Chain/Glue are the input chain/glue to use, and that TheCall is the call

test/CodeGen/Hexagon/namedreg.ll

+; RUN: llc -march=hexagon < %s | FileCheck %s
+define dso_local i32 @r19f() #0 {
+entry:
+  %0 = call i32 @llvm.read_register.i32(metadata !0)
+  ret i32 %0
+}
+
+; Function Attrs: noinline nounwind optnone
+define dso_local i32 @spf() #0 {
+entry:
+  %0 = call i32 @llvm.read_register.i32(metadata !1)
+  ret i32 %0
+}
+
+declare i32 @llvm.read_register.i32(metadata) #1
+
+!llvm.named.register.r19 = !{!0}
+!llvm.named.register.sp = !{!1}
+
+!0 = !{!"r19"}
+!1 = !{!"sp"}
+; CHECK: r0 = r19
+; CHECK: r0 = r29