[X86] Add a new LOW32_ADDR_ACCESS_RBP register class.

ABIs like NaCl uses 32-bit addresses but have 64-bit frame.
The new register class reflects those constraints when choosing a
register class for a address access.

llvm-svn: 268796

1 files changed, 9 insertions, 1 deletions

diff --git a/llvm/lib/Target/X86/X86RegisterInfo.cpp b/llvm/lib/Target/X86/X86RegisterInfo.cpp
index e32a5fdcdba..cb4170cc623 100644
--- a/llvm/lib/Target/X86/X86RegisterInfo.cpp
+++ b/llvm/lib/Target/X86/X86RegisterInfo.cpp
@@ -166,7 +166,15 @@ X86RegisterInfo::getPointerRegClass(const MachineFunction &MF,
     // we can still use 64-bit register as long as we know the high bits
     // are zeros.
     // Reflect that in the returned register class.
-    return Is64Bit ? &X86::LOW32_ADDR_ACCESSRegClass : &X86::GR32RegClass;
+    if (Is64Bit) {
+      // When the target also allows 64-bit frame pointer and we do have a
+      // frame, this is fine to use it for the address accesses as well.
+      const X86FrameLowering *TFI = getFrameLowering(MF);
+      return TFI->hasFP(MF) && TFI->Uses64BitFramePtr
+                 ? &X86::LOW32_ADDR_ACCESS_RBPRegClass
+                 : &X86::LOW32_ADDR_ACCESSRegClass;
+    }
+    return &X86::GR32RegClass;
   case 1: // Normal GPRs except the stack pointer (for encoding reasons).
     if (Subtarget.isTarget64BitLP64())
       return &X86::GR64_NOSPRegClass;