[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

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;

llvm/test/CodeGen/PowerPC/addi-licm.ll

@@ -0,0 +1,55 @@
+; RUN: llc -mcpu=pwr7 < %s | FileCheck %s
+target datalayout = "E-m:e-i64:64-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+; Function Attrs: nounwind
+define double @foo() #1 {
+entry:
+  %x = alloca [2048 x float], align 4
+  %y = alloca [2048 x float], align 4
+  %0 = bitcast [2048 x float]* %x to i8*
+  call void @llvm.lifetime.start(i64 8192, i8* %0) #2
+  %1 = bitcast [2048 x float]* %y to i8*
+  call void @llvm.lifetime.start(i64 8192, i8* %1) #2
+  br label %for.body.i
+
+; CHECK-LABEL: @foo
+; CHECK: addi [[REG1:[0-9]+]], 1,
+; CHECK: addi [[REG2:[0-9]+]], 1,
+; CHECK: %for.body.i
+; CHECK-DAG: lfsx {{[0-9]+}}, [[REG1]],
+; CHECK-DAG: lfsx {{[0-9]+}}, [[REG2]],
+; CHECK: blr
+
+for.body.i:                                       ; preds = %for.body.i.preheader, %for.body.i
+  %accumulator.09.i = phi double [ %add.i, %for.body.i ], [ 0.000000e+00, %entry ]
+  %i.08.i = phi i64 [ %inc.i, %for.body.i ], [ 0, %entry ]
+  %arrayidx.i = getelementptr inbounds [2048 x float]* %x, i64 0, i64 %i.08.i
+  %v14 = load float* %arrayidx.i, align 4
+  %conv.i = fpext float %v14 to double
+  %arrayidx1.i = getelementptr inbounds [2048 x float]* %y, i64 0, i64 %i.08.i
+  %v15 = load float* %arrayidx1.i, align 4
+  %conv2.i = fpext float %v15 to double
+  %mul.i = fmul double %conv.i, %conv2.i
+  %add.i = fadd double %accumulator.09.i, %mul.i
+  %inc.i = add nuw nsw i64 %i.08.i, 1
+  %exitcond.i = icmp eq i64 %i.08.i, 2047
+  br i1 %exitcond.i, label %loop.exit, label %for.body.i
+
+loop.exit:                                        ; preds = %for.body.i
+  ret double %accumulator.09.i
+}
+
+; Function Attrs: nounwind
+declare void @llvm.lifetime.start(i64, i8* nocapture) #2
+
+declare void @bar(float*, float*)
+
+; Function Attrs: nounwind
+declare void @llvm.lifetime.end(i64, i8* nocapture) #2
+
+attributes #0 = { nounwind readonly }
+attributes #1 = { nounwind }
+attributes #2 = { nounwind }
+
+