[PATCH] D73378: [SystemZ] Add implementation for the intrinsic llvm.read_register

[Yusra Syeda via Phabricator via llvm-commits]

yusra.syeda created this revision.
yusra.syeda added reviewers: uweigand, Kai.
yusra.syeda added a project: LLVM.
Herald added subscribers: llvm-commits, hiraditya, kristof.beyls.

This change implements the llvm intrinsic llvm.read_register for the SystemZ platform which returns the value of the specified register (http://llvm.org/docs/LangRef.html#llvm-read-register-and-llvm-write-register-intrinsics). This implementation returns the value of the stack register, and can be extended to return the value of other registers. The implementation for this intrinsic exists on various other platforms including Power, x86, ARM, etc. but missing on SystemZ.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73378

Files:
  llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
  llvm/lib/Target/SystemZ/SystemZISelLowering.h
  llvm/test/CodeGen/SystemZ/stackpointer.ll


Index: llvm/test/CodeGen/SystemZ/stackpointer.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/SystemZ/stackpointer.ll
@@ -0,0 +1,15 @@
+; RUN: llc < %s -mtriple=s390x-linux-gnu | FileCheck %s
+
+define i8* @get_stack() nounwind {
+entry:
+; CHECK-LABEL: get_stack:
+; CHECK: lgr %r2, %r15
+; CHECK-NEXT: br %r14
+        %0 = call i64 @llvm.read_register.i64(metadata !0)
+        %1 = inttoptr i64 %0 to i8*
+  ret i8* %1
+}
+
+declare i64 @llvm.read_register.i64(metadata) nounwind
+
+!0 = !{!"r15"}
Index: llvm/lib/Target/SystemZ/SystemZISelLowering.h
===================================================================
--- llvm/lib/Target/SystemZ/SystemZISelLowering.h
+++ llvm/lib/Target/SystemZ/SystemZISelLowering.h
@@ -471,6 +471,9 @@
     return TargetLowering::getInlineAsmMemConstraint(ConstraintCode);
   }
 
+  Register getRegisterByName(const char *RegName, LLT Ty,
+                             const MachineFunction &MF) const override;
+
   /// If a physical register, this returns the register that receives the
   /// exception address on entry to an EH pad.
   unsigned
Index: llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
===================================================================
--- llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
+++ llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
@@ -1179,6 +1179,19 @@
   return TargetLowering::getRegForInlineAsmConstraint(TRI, Constraint, VT);
 }
 
+// FIXME? Maybe this could be a TableGen attribute on some registers and
+// this table could be generated automatically from RegInfo.
+Register SystemZTargetLowering::getRegisterByName(const char *RegName, LLT Ty,
+                                                  const MachineFunction &MF) const {
+
+  Register Reg = StringSwitch<Register>(RegName)
+                   .Case("r15", SystemZ::R15D)
+                   .Default(0);
+  if (Reg)
+    return Reg;
+  report_fatal_error("Invalid register name global variable");
+}
+
 void SystemZTargetLowering::
 LowerAsmOperandForConstraint(SDValue Op, std::string &Constraint,
                              std::vector<SDValue> &Ops,


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