Not all targets have efficient ISel code generation for select instructions.

For example, the ARM target does not have efficient ISel handling for vector
selects with scalar conditions. This patch adds a TLI hook which allows the
different targets to report which selects are supported well and which selects
should be converted to CF duting codegen prepare.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163093 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 7 deletions

diff --git a/lib/Transforms/Scalar/CodeGenPrepare.cpp b/lib/Transforms/Scalar/CodeGenPrepare.cpp
index cfca726f26..57a648f7b9 100644
--- a/lib/Transforms/Scalar/CodeGenPrepare.cpp
+++ b/lib/Transforms/Scalar/CodeGenPrepare.cpp
@@ -1174,17 +1174,32 @@ static bool isFormingBranchFromSelectProfitable(SelectInst *SI) {
 }
 
 
+/// If we have a SelectInst that will likely profit from branch prediction,
+/// turn it into a branch.
 bool CodeGenPrepare::OptimizeSelectInst(SelectInst *SI) {
-  // If we have a SelectInst that will likely profit from branch prediction,
-  // turn it into a branch.
-  if (DisableSelectToBranch || OptSize || !TLI ||
-      !TLI->isPredictableSelectExpensive())
-    return false;
+  bool VectorCond = !SI->getCondition()->getType()->isIntegerTy(1);
 
-  if (!SI->getCondition()->getType()->isIntegerTy(1) ||
-      !isFormingBranchFromSelectProfitable(SI))
+  // Can we convert the 'select' to CF ?
+  if (DisableSelectToBranch || OptSize || !TLI || VectorCond)
     return false;
 
+  TargetLowering::SelectSupportKind SelectKind;
+  if (VectorCond)
+    SelectKind = TargetLowering::VectorMaskSelect;
+  else if (SI->getType()->isVectorTy())
+    SelectKind = TargetLowering::ScalarCondVectorVal;
+  else
+    SelectKind = TargetLowering::ScalarValSelect;
+
+  // Do we have efficient codegen support for this kind of 'selects' ?
+  if (TLI->isSelectSupported(SelectKind)) {
+    // We have efficient codegen support for the select instruction.
+    // Check if it is profitable to keep this 'select'.
+    if (!TLI->isPredictableSelectExpensive() ||
+        !isFormingBranchFromSelectProfitable(SI))
+      return false;
+  }
+
   ModifiedDT = true;
 
   // First, we split the block containing the select into 2 blocks.