Add support for ARM modified-immediate assembly syntax.

Certain ARM instructions accept 32-bit immediate operands encoded as a 8-bit
integer value (0-255) and a 4-bit rotation (0-30, even). Current ARM assembly
syntax support in LLVM allows the decoded (32-bit) immediate to be specified
as a single immediate operand for such instructions:

mov r0, #4278190080

The ARMARM defines an extended assembly syntax allowing the encoding to be made
more explicit, as in:

mov r0, #255, #8 ; (same 32-bit value as above)

The behaviour of the two instructions can be different w.r.t flags, which is
documented under "Modified immediate constants" in ARMARM. This patch enables
support for this extended syntax at the MC layer.

llvm-svn: 223113

1 files changed, 46 insertions, 0 deletions

diff --git a/llvm/lib/Target/ARM/InstPrinter/ARMInstPrinter.cpp b/llvm/lib/Target/ARM/InstPrinter/ARMInstPrinter.cpp
index 03e4e0a5e17..16eea335261 100644
--- a/llvm/lib/Target/ARM/InstPrinter/ARMInstPrinter.cpp
+++ b/llvm/lib/Target/ARM/InstPrinter/ARMInstPrinter.cpp
@@ -1318,6 +1318,52 @@ void ARMInstPrinter::printRotImmOperand(const MCInst *MI, unsigned OpNum,
   O << markup(">");
 }
 
+void ARMInstPrinter::printModImmOperand(const MCInst *MI, unsigned OpNum,
+                                        raw_ostream &O) {
+  MCOperand Op = MI->getOperand(OpNum);
+
+  // Support for fixups (MCFixup)
+  if (Op.isExpr())
+    return printOperand(MI, OpNum, O);
+
+  unsigned Bits = Op.getImm() & 0xFF;
+  unsigned Rot = (Op.getImm() & 0xF00) >> 7;
+
+  bool  PrintUnsigned = false;
+  switch (MI->getOpcode()){
+  case ARM::MOVi:
+    // Movs to PC should be treated unsigned
+    PrintUnsigned = (MI->getOperand(OpNum - 1).getReg() == ARM::PC);
+    break;
+  case ARM::MSRi:
+    // Movs to special registers should be treated unsigned
+    PrintUnsigned = true;
+    break;
+  }
+
+  int32_t Rotated = ARM_AM::rotr32(Bits, Rot);
+  if (ARM_AM::getSOImmVal(Rotated) == Op.getImm()) {
+    // #rot has the least possible value
+    O << "#" << markup("<imm:");
+    if (PrintUnsigned)
+      O << static_cast<uint32_t>(Rotated);
+    else
+      O << Rotated;
+    O << markup(">");
+    return;
+  }
+
+  // Explicit #bits, #rot implied
+  O << "#"
+    << markup("<imm:")
+    << Bits
+    << markup(">")
+    << ", #"
+    << markup("<imm:")
+    << Rot
+    << markup(">");
+}
+
 void ARMInstPrinter::printFBits16(const MCInst *MI, unsigned OpNum,
                                   raw_ostream &O) {
   O << markup("<imm:")