AArch64: allow MOV (imm) alias to be printed

The backend has been around for years, it's pretty ridiculous that we can't
even use the preferred form for printing "MOV" aliases. Unfortunately, TableGen
can't handle the complex predicates when printing so it's a bunch of nasty C++.
Oh well.

llvm-svn: 272865

1 files changed, 48 insertions, 0 deletions

diff --git a/llvm/lib/Target/AArch64/InstPrinter/AArch64InstPrinter.cpp b/llvm/lib/Target/AArch64/InstPrinter/AArch64InstPrinter.cpp
index 06883712e7a..a3669cf18e7 100644
--- a/llvm/lib/Target/AArch64/InstPrinter/AArch64InstPrinter.cpp
+++ b/llvm/lib/Target/AArch64/InstPrinter/AArch64InstPrinter.cpp
@@ -219,6 +219,54 @@ void AArch64InstPrinter::printInst(const MCInst *MI, raw_ostream &O,
     return;
   }
 
+  // MOVZ, MOVN and "ORR wzr, #imm" instructions are aliases for MOV, but their
+  // domains overlap so they need to be prioritized. The chain is "MOVZ lsl #0 >
+  // MOVZ lsl #N > MOVN lsl #0 > MOVN lsl #N > ORR". The highest instruction
+  // that can represent the move is the MOV alias, and the rest get printed
+  // normally.
+  if ((Opcode == AArch64::MOVZXi || Opcode == AArch64::MOVZWi) &&
+      MI->getOperand(1).isImm() && MI->getOperand(2).isImm()) {
+    int RegWidth = Opcode == AArch64::MOVZXi ? 64 : 32;
+    int Shift = MI->getOperand(2).getImm();
+    uint64_t Value = (uint64_t)MI->getOperand(1).getImm() << Shift;
+
+    if (AArch64_AM::isMOVZMovAlias(Value, Shift,
+                                   Opcode == AArch64::MOVZXi ? 64 : 32)) {
+      O << "\tmov\t" << getRegisterName(MI->getOperand(0).getReg()) << ", #"
+        << formatImm(SignExtend64(Value, RegWidth));
+      return;
+    }
+  }
+
+  if ((Opcode == AArch64::MOVNXi || Opcode == AArch64::MOVNWi) &&
+      MI->getOperand(1).isImm() && MI->getOperand(2).isImm()) {
+    int RegWidth = Opcode == AArch64::MOVNXi ? 64 : 32;
+    int Shift = MI->getOperand(2).getImm();
+    uint64_t Value = ~((uint64_t)MI->getOperand(1).getImm() << Shift);
+    if (RegWidth == 32)
+      Value = Value & 0xffffffff;
+
+    if (AArch64_AM::isMOVNMovAlias(Value, Shift, RegWidth)) {
+      O << "\tmov\t" << getRegisterName(MI->getOperand(0).getReg()) << ", #"
+        << formatImm(SignExtend64(Value, RegWidth));
+      return;
+    }
+  }
+
+  if ((Opcode == AArch64::ORRXri || Opcode == AArch64::ORRWri) &&
+      (MI->getOperand(1).getReg() == AArch64::XZR ||
+       MI->getOperand(1).getReg() == AArch64::WZR) &&
+      MI->getOperand(2).isImm()) {
+    int RegWidth = Opcode == AArch64::ORRXri ? 64 : 32;
+    uint64_t Value = AArch64_AM::decodeLogicalImmediate(
+        MI->getOperand(2).getImm(), RegWidth);
+    if (!AArch64_AM::isAnyMOVWMovAlias(Value, RegWidth)) {
+      O << "\tmov\t" << getRegisterName(MI->getOperand(0).getReg()) << ", #"
+        << formatImm(SignExtend64(Value, RegWidth));
+      return;
+    }
+  }
+
   if (!printAliasInstr(MI, STI, O))
     printInstruction(MI, STI, O);