Mark FPB as a reserved register when needed.

llvm-svn: 205421

2 files changed, 15 insertions, 1 deletions

diff --git a/llvm/lib/Target/MSP430/MSP430RegisterInfo.cpp b/llvm/lib/Target/MSP430/MSP430RegisterInfo.cpp
index 578443167c0..f64017ef253 100644
--- a/llvm/lib/Target/MSP430/MSP430RegisterInfo.cpp
+++ b/llvm/lib/Target/MSP430/MSP430RegisterInfo.cpp
@@ -88,8 +88,10 @@ BitVector MSP430RegisterInfo::getReservedRegs(const MachineFunction &MF) const {
   Reserved.set(MSP430::CGW);
 
   // Mark frame pointer as reserved if needed.
-  if (TFI->hasFP(MF))
+  if (TFI->hasFP(MF)) {
+    Reserved.set(MSP430::FPB);
     Reserved.set(MSP430::FPW);
+  }
 
   return Reserved;
 }
diff --git a/llvm/test/CodeGen/MSP430/fp.ll b/llvm/test/CodeGen/MSP430/fp.ll
index 018090566f1..b6ba22e47cc 100644
--- a/llvm/test/CodeGen/MSP430/fp.ll
+++ b/llvm/test/CodeGen/MSP430/fp.ll
@@ -15,3 +15,15 @@ entry:
 ; CHECK: pop.w r4
   ret void
 }
+
+; Due to FPB not being marked as reserved, the register allocator used to select
+; r4 as the register for the "r" constraint below. This test verifies that this
+; does not happen anymore. Note that the only reason an ISR is used here is that
+; the register allocator selects r4 first instead of fifth in a normal function.
+define msp430_intrcc void @fpb_alloced() #0 {
+; CHECK_LABEL: fpb_alloced:
+; CHECK-NOT: mov.b #0, r4
+; CHECK: nop
+  call void asm sideeffect "nop", "r"(i8 0)
+  ret void
+}