R600: Make cttz / ctlz cheap to speculate

Speculating things is generally good. SI+ has instructions for these
for 32-bit values. This is still probably better even with the expansion
for 64-bit values, although it is odd that this callback doesn't have
the size as a parameter.

llvm-svn: 225822

2 files changed, 15 insertions, 0 deletions

diff --git a/llvm/lib/Target/R600/AMDGPUISelLowering.cpp b/llvm/lib/Target/R600/AMDGPUISelLowering.cpp
index 82d15ada668..b8dc83b8fb1 100644
--- a/llvm/lib/Target/R600/AMDGPUISelLowering.cpp
+++ b/llvm/lib/Target/R600/AMDGPUISelLowering.cpp
@@ -471,6 +471,18 @@ bool AMDGPUTargetLowering::isLoadBitCastBeneficial(EVT LoadTy,
           (LScalarSize < 32));
 }
 
+// SI+ has instructions for cttz / ctlz for 32-bit values. This is probably also
+// profitable with the expansion for 64-bit since it's generally good to
+// speculate things.
+// FIXME: These should really have the size as a parameter.
+bool AMDGPUTargetLowering::isCheapToSpeculateCttz() const {
+  return true;
+}
+
+bool AMDGPUTargetLowering::isCheapToSpeculateCtlz() const {
+  return true;
+}
+
 //===---------------------------------------------------------------------===//
 // Target Properties
 //===---------------------------------------------------------------------===//
diff --git a/llvm/lib/Target/R600/AMDGPUISelLowering.h b/llvm/lib/Target/R600/AMDGPUISelLowering.h
index 6571c0b00a5..a653ae5a7ff 100644
--- a/llvm/lib/Target/R600/AMDGPUISelLowering.h
+++ b/llvm/lib/Target/R600/AMDGPUISelLowering.h
@@ -129,6 +129,9 @@ public:
                              EVT ExtVT) const override;
 
   bool isLoadBitCastBeneficial(EVT, EVT) const override;
+  bool isCheapToSpeculateCttz() const override;
+  bool isCheapToSpeculateCtlz() const override;
+
   SDValue LowerReturn(SDValue Chain, CallingConv::ID CallConv,
                       bool isVarArg,
                       const SmallVectorImpl<ISD::OutputArg> &Outs,