R600: Implement getRecipEstimate

This requires a new hook to prevent expanding sqrt in terms
of rsqrt and reciprocal. v_rcp_f32, v_rsq_f32, and v_sqrt_f32 are
all the same rate, so this expansion would just double the number
of instructions and cycles.

llvm-svn: 225828

2 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 171ee1e3488..e57c5a2b1ac 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7538,7 +7538,8 @@ SDValue DAGCombiner::visitFREM(SDNode *N) {
 }
 
 SDValue DAGCombiner::visitFSQRT(SDNode *N) {
-  if (DAG.getTarget().Options.UnsafeFPMath) {
+  if (DAG.getTarget().Options.UnsafeFPMath &&
+      !TLI.isFsqrtCheap()) {
     // Compute this as X * (1/sqrt(X)) = X * (X ** -0.5)
     if (SDValue RV = BuildRsqrtEstimate(N->getOperand(0))) {
       EVT VT = RV.getValueType();
diff --git a/llvm/lib/CodeGen/TargetLoweringBase.cpp b/llvm/lib/CodeGen/TargetLoweringBase.cpp
index fae54d2c304..9b2fdffa87c 100644
--- a/llvm/lib/CodeGen/TargetLoweringBase.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringBase.cpp
@@ -710,6 +710,7 @@ TargetLoweringBase::TargetLoweringBase(const TargetMachine &tm)
   HasMultipleConditionRegisters = false;
   HasExtractBitsInsn = false;
   IntDivIsCheap = false;
+  FsqrtIsCheap = false;
   Pow2SDivIsCheap = false;
   JumpIsExpensive = false;
   PredictableSelectIsExpensive = false;