1 files changed, 10 insertions, 3 deletions
diff --git a/llvm/lib/CodeGen/RegisterClassInfo.cpp b/llvm/lib/CodeGen/RegisterClassInfo.cpp
index 1523bd4d1649..0488db3d09cb 100644
--- a/llvm/lib/CodeGen/RegisterClassInfo.cpp
+++ b/llvm/lib/CodeGen/RegisterClassInfo.cpp
@@ -188,7 +188,14 @@ unsigned RegisterClassInfo::computePSetLimit(unsigned Idx) const {
   }
   assert(RC && "Failed to find register class");
   compute(RC);
-  unsigned NReserved = RC->getNumRegs() - getNumAllocatableRegs(RC);
-  return TRI->getRegPressureSetLimit(*MF, Idx) -
-         TRI->getRegClassWeight(RC).RegWeight * NReserved;
+  unsigned NAllocatableRegs = getNumAllocatableRegs(RC);
+  unsigned RegPressureSetLimit = TRI->getRegPressureSetLimit(*MF, Idx);
+  // If all the regs are reserved, return raw RegPressureSetLimit.
+  // One example is VRSAVERC in PowerPC.
+  // Avoid returning zero, getRegPressureSetLimit(Idx) assumes computePSetLimit
+  // return non-zero value.
+  if (NAllocatableRegs == 0)
+    return RegPressureSetLimit;
+  unsigned NReserved = RC->getNumRegs() - NAllocatableRegs;
+  return RegPressureSetLimit - TRI->getRegClassWeight(RC).RegWeight * NReserved;
 }