[PATCH] D63471: AArch64: Add support for reading pc using llvm.read_register.

[Peter Collingbourne via Phabricator via llvm-commits]

pcc updated this revision to Diff 206111.
pcc added a comment.

- Instead of defining a pseudo-instruction, simply use the immediate form of the ADR instruction


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D63471/new/

https://reviews.llvm.org/D63471

Files:
  llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
  llvm/test/CodeGen/AArch64/read-pc.ll


Index: llvm/test/CodeGen/AArch64/read-pc.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AArch64/read-pc.ll
@@ -0,0 +1,11 @@
+; RUN: llc < %s -mtriple=arm64-linux-gnu | FileCheck %s
+
+define i64 @read_pc() {
+  ; CHECK: adr x0, #0
+  %pc = call i64 @llvm.read_register.i64(metadata !0)
+  ret i64 %pc
+}
+
+declare i64 @llvm.read_register.i64(metadata) nounwind
+
+!0 = !{!"pc"}
Index: llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
===================================================================
--- llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
+++ llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
@@ -2678,6 +2678,14 @@
     return true;
   }
 
+  if (RegString->getString() == "pc") {
+    ReplaceNode(N, CurDAG->getMachineNode(
+                       AArch64::ADR, DL, N->getSimpleValueType(0), MVT::Other,
+                       CurDAG->getTargetConstant(0, DL, MVT::i32),
+                       N->getOperand(0)));
+    return true;
+  }
+
   return false;
 }
 


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