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

diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index acf0419510e939b9e5c7f5f19de79a9b483ebc41..b8c070bce75948fdacf6369a4d2c9a95b00b4f8d 100644 (file)
--- a/include/llvm/Target/TargetLowering.h
+++ b/include/llvm/Target/TargetLowering.h
@@ -107,6 +107,14 @@ public:
     ZeroOrNegativeOneBooleanContent // All bits equal to bit 0.
   };
 
+  enum SelectSupportKind {
+    ScalarValSelect,      // The target supports scalar selects (ex: cmov).
+    ScalarCondVectorVal,  // The target supports selects with a scalar condition
+                          // and vector values (ex: cmov).
+    VectorMaskSelect      // The target supports vector selects with a vector
+                          // mask (ex: x86 blends).
+  };
+
   static ISD::NodeType getExtendForContent(BooleanContent Content) {
     switch (Content) {
     case UndefinedBooleanContent:
@@ -140,6 +148,8 @@ public:
   /// this target.
   bool isSelectExpensive() const { return SelectIsExpensive; }
 
+  virtual bool isSelectSupported(SelectSupportKind kind) const { return true; }
+
   /// isIntDivCheap() - Return true if integer divide is usually cheaper than
   /// a sequence of several shifts, adds, and multiplies for this target.
   bool isIntDivCheap() const { return IntDivIsCheap; }

diff --git a/lib/Target/ARM/ARMISelLowering.h b/lib/Target/ARM/ARMISelLowering.h
index 13b83de85d3c62a5fa419b2511cff9e877fde774..757c68ee3700162feddff42441b46fc8329e1445 100644 (file)
--- a/lib/Target/ARM/ARMISelLowering.h
+++ b/lib/Target/ARM/ARMISelLowering.h
@@ -257,6 +257,11 @@ namespace llvm {
 
     virtual const char *getTargetNodeName(unsigned Opcode) const;
 
+    virtual bool isSelectSupported(SelectSupportKind Kind) const {
+      // ARM does not support scalar condition selects on vectors.
+      return (Kind != ScalarCondVectorVal);
+    }
+
     /// getSetCCResultType - Return the value type to use for ISD::SETCC.
     virtual EVT getSetCCResultType(EVT VT) const;
 

diff --git a/lib/Transforms/Scalar/CodeGenPrepare.cpp b/lib/Transforms/Scalar/CodeGenPrepare.cpp
index cfca726f2697d27224af7974fcf3422e2f7529ba..57a648f7b9714e2bc4b65c44339fbce4d9464bc1 100644 (file)
--- 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.

diff --git a/test/CodeGen/ARM/2012-08-30-select.ll b/test/CodeGen/ARM/2012-08-30-select.ll
index 4c94ac9dbf0599ce7027d9fd067a08fbcabe744e..8471be5330b85175e2975f1bf534aca09b37183d 100644 (file)
--- a/test/CodeGen/ARM/2012-08-30-select.ll
+++ b/test/CodeGen/ARM/2012-08-30-select.ll
@@ -2,9 +2,8 @@
 ; rdar://12201387
 
 ;CHECK: select_s_v_v
-;CHECK: it  eq
-;CHECK-NEXT: moveq.w r2, #-1
-;CHECK: vbsl
+;CHECK: it  ne
+;CHECK-NEXT: vmovne.i32
 ;CHECK: bx
 define <16 x i8> @select_s_v_v(i32 %avail, i8* %bar) {
 entry: