[AArch64] Add Tiny Code Model for AArch64

This adds the plumbing for the Tiny code model for the AArch64 backend. This,
instead of loading addresses through the normal ADRP;ADD pair used in the Small
model, uses a single ADR. The 21 bit range of an ADR means that the code and
its statically defined symbols need to be within 1MB of each other.

This makes it mostly interesting for embedded applications where we want to fit
as much as we can in as small a space as possible.

Differential Revision: https://reviews.llvm.org/D49673

llvm-svn: 340397

1 files changed, 44 insertions, 25 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64ExpandPseudoInsts.cpp b/llvm/lib/Target/AArch64/AArch64ExpandPseudoInsts.cpp
index 9226a9dd879..f7190d58fbf 100644
--- a/llvm/lib/Target/AArch64/AArch64ExpandPseudoInsts.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ExpandPseudoInsts.cpp
@@ -835,36 +835,55 @@ bool AArch64ExpandPseudo::expandMI(MachineBasicBlock &MBB,
   }
 
   case AArch64::LOADgot: {
-    // Expand into ADRP + LDR.
+    MachineFunction *MF = MBB.getParent();
     unsigned DstReg = MI.getOperand(0).getReg();
     const MachineOperand &MO1 = MI.getOperand(1);
     unsigned Flags = MO1.getTargetFlags();
-    MachineInstrBuilder MIB1 =
-        BuildMI(MBB, MBBI, MI.getDebugLoc(), TII->get(AArch64::ADRP), DstReg);
-    MachineInstrBuilder MIB2 =
-        BuildMI(MBB, MBBI, MI.getDebugLoc(), TII->get(AArch64::LDRXui))
-            .add(MI.getOperand(0))
-            .addReg(DstReg);
-
-    if (MO1.isGlobal()) {
-      MIB1.addGlobalAddress(MO1.getGlobal(), 0, Flags | AArch64II::MO_PAGE);
-      MIB2.addGlobalAddress(MO1.getGlobal(), 0,
-                            Flags | AArch64II::MO_PAGEOFF | AArch64II::MO_NC);
-    } else if (MO1.isSymbol()) {
-      MIB1.addExternalSymbol(MO1.getSymbolName(), Flags | AArch64II::MO_PAGE);
-      MIB2.addExternalSymbol(MO1.getSymbolName(),
-                             Flags | AArch64II::MO_PAGEOFF | AArch64II::MO_NC);
+
+    if (MF->getTarget().getCodeModel() == CodeModel::Tiny) {
+      // Tiny codemodel expand to LDR
+      MachineInstrBuilder MIB = BuildMI(MBB, MBBI, MI.getDebugLoc(),
+                                        TII->get(AArch64::LDRXl), DstReg);
+
+      if (MO1.isGlobal()) {
+        MIB.addGlobalAddress(MO1.getGlobal(), 0, Flags);
+      } else if (MO1.isSymbol()) {
+        MIB.addExternalSymbol(MO1.getSymbolName(), Flags);
+      } else {
+        assert(MO1.isCPI() &&
+               "Only expect globals, externalsymbols, or constant pools");
+        MIB.addConstantPoolIndex(MO1.getIndex(), MO1.getOffset(), Flags);
+      }
     } else {
-      assert(MO1.isCPI() &&
-             "Only expect globals, externalsymbols, or constant pools");
-      MIB1.addConstantPoolIndex(MO1.getIndex(), MO1.getOffset(),
-                                Flags | AArch64II::MO_PAGE);
-      MIB2.addConstantPoolIndex(MO1.getIndex(), MO1.getOffset(),
-                                Flags | AArch64II::MO_PAGEOFF |
-                                    AArch64II::MO_NC);
+      // Small codemodel expand into ADRP + LDR.
+      MachineInstrBuilder MIB1 =
+          BuildMI(MBB, MBBI, MI.getDebugLoc(), TII->get(AArch64::ADRP), DstReg);
+      MachineInstrBuilder MIB2 =
+          BuildMI(MBB, MBBI, MI.getDebugLoc(), TII->get(AArch64::LDRXui))
+              .add(MI.getOperand(0))
+              .addReg(DstReg);
+
+      if (MO1.isGlobal()) {
+        MIB1.addGlobalAddress(MO1.getGlobal(), 0, Flags | AArch64II::MO_PAGE);
+        MIB2.addGlobalAddress(MO1.getGlobal(), 0,
+                              Flags | AArch64II::MO_PAGEOFF | AArch64II::MO_NC);
+      } else if (MO1.isSymbol()) {
+        MIB1.addExternalSymbol(MO1.getSymbolName(), Flags | AArch64II::MO_PAGE);
+        MIB2.addExternalSymbol(MO1.getSymbolName(), Flags |
+                                                        AArch64II::MO_PAGEOFF |
+                                                        AArch64II::MO_NC);
+      } else {
+        assert(MO1.isCPI() &&
+               "Only expect globals, externalsymbols, or constant pools");
+        MIB1.addConstantPoolIndex(MO1.getIndex(), MO1.getOffset(),
+                                  Flags | AArch64II::MO_PAGE);
+        MIB2.addConstantPoolIndex(MO1.getIndex(), MO1.getOffset(),
+                                  Flags | AArch64II::MO_PAGEOFF |
+                                      AArch64II::MO_NC);
+      }
+
+      transferImpOps(MI, MIB1, MIB2);
     }
-
-    transferImpOps(MI, MIB1, MIB2);
     MI.eraseFromParent();
     return true;
   }