[PowerPC] Mark all instructions as non-cheap for MachineLICM

MachineLICM uses a callback named hasLowDefLatency to determine if an
instruction def operand has a 'low' latency. If all relevant operands have a
'low' latency, the instruction is considered too cheap to hoist out of loops
even in low-register-pressure situations. On PowerPC cores, both the embedded
cores and the others, there is no reason to believe that this is a good choice:
all instructions have a cost inside a loop, and hoisting them when not limited
by register pressure is a reasonable default.

llvm-svn: 225471

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.h b/llvm/lib/Target/PowerPC/PPCInstrInfo.h
index 4d310fee47b..4add6f9781e 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.h
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.h
@@ -106,6 +106,15 @@ public:
                                               UseNode, UseIdx);
   }
 
+  bool hasLowDefLatency(const InstrItineraryData *ItinData,
+                        const MachineInstr *DefMI,
+                        unsigned DefIdx) const override {
+    // Machine LICM should hoist all instructions in low-register-pressure
+    // situations; none are sufficiently free to justify leaving in a loop
+    // body.
+    return false;
+  }
+
   bool isCoalescableExtInstr(const MachineInstr &MI,
                              unsigned &SrcReg, unsigned &DstReg,
                              unsigned &SubIdx) const override;