Use TargetTransformInfo to control switch-to-lookup table transformation

When the switch-to-lookup tables transform landed in SimplifyCFG, it
was pointed out that this could be inappropriate for some targets.
Since there was no way at the time for the pass to know anything about
the target, an awkward reverse-transform was added in CodeGenPrepare
that turned lookup tables back into switches for some targets.

This patch uses the new TargetTransformInfo to determine if a
switch should be transformed, and removes
CodeGenPrepare::ConvertLoadToSwitch.

llvm-svn: 167011

1 files changed, 6 insertions, 1 deletions

diff --git a/llvm/lib/Target/TargetTransformImpl.cpp b/llvm/lib/Target/TargetTransformImpl.cpp
index 27877a9..38c704f 100644
--- a/llvm/lib/Target/TargetTransformImpl.cpp
+++ b/llvm/lib/Target/TargetTransformImpl.cpp
@@ -49,6 +49,12 @@ unsigned ScalarTargetTransformImpl::getJumpBufSize() const {
   return TLI->getJumpBufSize();
 }
 
+bool ScalarTargetTransformImpl::shouldBuildLookupTables() const {
+  return TLI->supportJumpTables() &&
+      (TLI->isOperationLegalOrCustom(ISD::BR_JT, MVT::Other) ||
+       TLI->isOperationLegalOrCustom(ISD::BRIND, MVT::Other));
+}
+
 //===----------------------------------------------------------------------===//
 //
 // Calls used by the vectorizers.
@@ -313,4 +319,3 @@ VectorTargetTransformImpl::getNumberOfParts(Type *Tp) const {
     getTypeLegalizationCost(Tp->getContext(), TLI->getValueType(Tp));
   return LT.first;
 }
-