[PATCH] D138615: [llvm] Teach FastISel for AArch64 about tagged globals

[Leonard Chan via Phabricator via llvm-commits]

leonardchan created this revision.
leonardchan added reviewers: pcc, vitalybuka, eugenis.
leonardchan added a project: LLVM.
Herald added subscribers: hiraditya, kristof.beyls.
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leonardchan requested review of this revision.

This addresses https://github.com/llvm/llvm-project/issues/57750. For some globals, the tag wasn't propagated correctly because the necessary `movk` wasn't emitted sometimes.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D138615

Files:
  llvm/lib/Target/AArch64/AArch64FastISel.cpp


Index: llvm/lib/Target/AArch64/AArch64FastISel.cpp
===================================================================
--- llvm/lib/Target/AArch64/AArch64FastISel.cpp
+++ llvm/lib/Target/AArch64/AArch64FastISel.cpp
@@ -496,6 +496,20 @@
             ADRPReg)
         .addGlobalAddress(GV, 0, AArch64II::MO_PAGE | OpFlags);
 
+    if (OpFlags & AArch64II::MO_TAGGED) {
+      // MO_TAGGED on the page indicates a tagged address. Set the tag now.
+      // We do so by creating a MOVK that sets bits 48-63 of the register to
+      // (global address + 0x100000000 - PC) >> 48. This assumes that we're in
+      // the small code model so we can assume a binary size of <= 4GB, which
+      // makes the untagged PC relative offset positive. The binary must also be
+      // loaded into address range [0, 2^48). Both of these properties need to
+      // be ensured at runtime when using tagged addresses.
+      BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, MIMD, TII.get(AArch64::MOVKXi), ADRPReg)
+          .addReg(ADRPReg)
+          .addGlobalAddress(GV, /*Offset=*/0x100000000, AArch64II::MO_PREL | AArch64II::MO_G3)
+          .addImm(48);
+    }
+
     ResultReg = createResultReg(&AArch64::GPR64spRegClass);
     BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, MIMD, TII.get(AArch64::ADDXri),
             ResultReg)


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