From 9f40cb32ac31283f8636d516e7b10f3ad921955c Mon Sep 17 00:00:00 2001
From: Nadav Rotem <nrotem@apple.com>
Date: Sun, 2 Sep 2012 12:10:19 +0000
Subject: [PATCH] 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
---
 include/llvm/Target/TargetLowering.h     | 10 ++++++++
 lib/Target/ARM/ARMISelLowering.h         |  5 ++++
 lib/Transforms/Scalar/CodeGenPrepare.cpp | 29 ++++++++++++++++++------
 test/CodeGen/ARM/2012-08-30-select.ll    |  5 ++--
 4 files changed, 39 insertions(+), 10 deletions(-)

diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index acf0419510e..b8c070bce75 100644
--- 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 13b83de85d3..757c68ee370 100644
--- 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 cfca726f269..57a648f7b97 100644
--- a/lib/Transforms/Scalar/CodeGenPrepare.cpp
+++ b/lib/Transforms/Scalar/CodeGenPrepare.cpp
@@ -1174,16 +1174,31 @@ 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())
+  bool VectorCond = !SI->getCondition()->getType()->isIntegerTy(1);
+
+  // Can we convert the 'select' to CF ?
+  if (DisableSelectToBranch || OptSize || !TLI || VectorCond)
     return false;
 
-  if (!SI->getCondition()->getType()->isIntegerTy(1) ||
-      !isFormingBranchFromSelectProfitable(SI))
-    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;
 
diff --git a/test/CodeGen/ARM/2012-08-30-select.ll b/test/CodeGen/ARM/2012-08-30-select.ll
index 4c94ac9dbf0..8471be5330b 100644
--- 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: