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
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
index b8ee555..7320f40 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
@@ -304,6 +304,28 @@
return Binary;
}
+ unsigned getModImmOpValue(const MCInst &MI, unsigned Op,
+ SmallVectorImpl<MCFixup> &Fixups,
+ const MCSubtargetInfo &ST) const {
+ const MCOperand &MO = MI.getOperand(Op);
+
+ // Support for fixups (MCFixup)
+ if (MO.isExpr()) {
+ const MCExpr *Expr = MO.getExpr();
+ // In instruction code this value always encoded as lowest 12 bits,
+ // so we don't have to perform any specific adjustments.
+ // Due to requirements of relocatable records we have to use FK_Data_4.
+ // See ARMELFObjectWriter::ExplicitRelSym and
+ // ARMELFObjectWriter::GetRelocTypeInner for more details.
+ MCFixupKind Kind = MCFixupKind(FK_Data_4);
+ Fixups.push_back(MCFixup::Create(0, Expr, Kind, MI.getLoc()));
+ return 0;
+ }
+
+ // Immediate is already in its encoded format
+ return MO.getImm();
+ }
+
/// getT2SOImmOpValue - Return an encoded 12-bit shifted-immediate value.
unsigned getT2SOImmOpValue(const MCInst &MI, unsigned Op,
SmallVectorImpl<MCFixup> &Fixups,