ARM IAS: support emitting constant values in target expressions

A 32-bit immediate value can be formed from a constant expression and loaded
into a register.  Add support to emit this into an object file.  Because this
value is a constant, a relocation must *not* be produced for it.

llvm-svn: 199023

1 files changed, 15 insertions, 0 deletions

diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
index 25a3d4df435..4c0098f8e9d 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
@@ -26,6 +26,7 @@
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCSubtargetInfo.h"
+#include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace llvm;
@@ -912,6 +913,20 @@ ARMMCCodeEmitter::getHiLo16ImmOpValue(const MCInst &MI, unsigned OpIdx,
     const ARMMCExpr *ARM16Expr = cast<ARMMCExpr>(E);
     E = ARM16Expr->getSubExpr();
 
+    if (const MCConstantExpr *MCE = dyn_cast<MCConstantExpr>(E)) {
+      const int64_t Value = MCE->getValue();
+      if (Value > UINT32_MAX)
+        report_fatal_error("constant value truncated (limited to 32-bit)");
+
+      switch (ARM16Expr->getKind()) {
+      case ARMMCExpr::VK_ARM_HI16:
+        return (int32_t(Value) & 0xffff0000) >> 16;
+      case ARMMCExpr::VK_ARM_LO16:
+        return (int32_t(Value) & 0x0000ffff);
+      default: llvm_unreachable("Unsupported ARMFixup");
+      }
+    }
+
     switch (ARM16Expr->getKind()) {
     default: llvm_unreachable("Unsupported ARMFixup");
     case ARMMCExpr::VK_ARM_HI16: