[PowerPC] Enable speculation of cttz/ctlz

PPC has an instruction for ctlz with defined zero behavior, and our lowering of
cttz (provided by DAGCombine) is also efficient and branchless, so speculating
these makes sense.

llvm-svn: 225150

2 files changed, 49 insertions, 0 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index d9142c7e7d0..dd2431e9579 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -387,6 +387,14 @@ namespace llvm {
 
     MVT getScalarShiftAmountTy(EVT LHSTy) const override { return MVT::i32; }
 
+    bool isCheapToSpeculateCttz() const override {
+      return true;
+    }
+
+    bool isCheapToSpeculateCtlz() const override {
+      return true;
+    }
+
     /// getSetCCResultType - Return the ISD::SETCC ValueType
     EVT getSetCCResultType(LLVMContext &Context, EVT VT) const override;
 
diff --git a/llvm/test/CodeGen/PowerPC/cttz-ctlz-spec.ll b/llvm/test/CodeGen/PowerPC/cttz-ctlz-spec.ll
new file mode 100644
index 00000000000..13b017a746e
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/cttz-ctlz-spec.ll
@@ -0,0 +1,41 @@
+; RUN: opt -S -codegenprepare < %s | FileCheck %s
+target datalayout = "E-m:e-i64:64-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+define i64 @test1(i64 %A) {
+; CHECK-LABEL: @test1(
+; CHECK: [[CTLZ:%[A-Za-z0-9]+]] = call i64 @llvm.ctlz.i64(i64 %A, i1 false)
+; CHECK-NEXT: ret i64 [[CTLZ]]
+entry:
+  %tobool = icmp eq i64 %A, 0
+  br i1 %tobool, label %cond.end, label %cond.true
+
+cond.true:                                        ; preds = %entry
+  %0 = tail call i64 @llvm.ctlz.i64(i64 %A, i1 true)
+  br label %cond.end
+
+cond.end:                                         ; preds = %entry, %cond.true
+  %cond = phi i64 [ %0, %cond.true ], [ 64, %entry ]
+  ret i64 %cond
+}
+
+define i64 @test1b(i64 %A) {
+; CHECK-LABEL: @test1b(
+; CHECK: [[CTTZ:%[A-Za-z0-9]+]] = call i64 @llvm.cttz.i64(i64 %A, i1 false)
+; CHECK-NEXT: ret i64 [[CTTZ]]
+entry:
+  %tobool = icmp eq i64 %A, 0
+  br i1 %tobool, label %cond.end, label %cond.true
+
+cond.true:                                        ; preds = %entry
+  %0 = tail call i64 @llvm.cttz.i64(i64 %A, i1 true)
+  br label %cond.end
+
+cond.end:                                         ; preds = %entry, %cond.true
+  %cond = phi i64 [ %0, %cond.true ], [ 64, %entry ]
+  ret i64 %cond
+}
+
+declare i64 @llvm.ctlz.i64(i64, i1)
+declare i64 @llvm.cttz.i64(i64, i1)
+