From 9a3dc552022e0e034ef34da889f6ceb9de260c96 Mon Sep 17 00:00:00 2001
From: Nate Begeman <natebegeman@mac.com>
Date: Fri, 17 Dec 2010 23:12:19 +0000
Subject: [PATCH] Add vector versions of some existing scalar transforms to aid
 codegen in matching psign & pblend operations to the IR produced by clang/gcc
 for their C idioms.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122105 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ValueTracking.cpp                |  7 ++++++
 .../InstCombine/InstCombineCasts.cpp          | 17 ++++++++++++++
 test/Transforms/InstCombine/vec_sext.ll       | 22 +++++++++++++++++++
 3 files changed, 46 insertions(+)
 create mode 100644 test/Transforms/InstCombine/vec_sext.ll

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 75062953cba..f8145cd0e3d 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -678,6 +678,13 @@ unsigned llvm::ComputeNumSignBits(Value *V, const TargetData *TD,
       Tmp += C->getZExtValue();
       if (Tmp > TyBits) Tmp = TyBits;
     }
+    // vector ashr X, <C, C, C, C>  -> adds C sign bits
+    if (ConstantVector *C = dyn_cast<ConstantVector>(U->getOperand(1))) {
+      if (ConstantInt *CI = dyn_cast_or_null<ConstantInt>(C->getSplatValue())) {
+        Tmp += CI->getZExtValue();
+        if (Tmp > TyBits) Tmp = TyBits;
+      }
+    }
     return Tmp;
   case Instruction::Shl:
     if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) {
diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 79a9b09c64d..df2abb5cef2 100644
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1020,6 +1020,23 @@ Instruction *InstCombiner::visitSExt(SExtInst &CI) {
   }
   }
   
+  // vector (x <s 0) ? -1 : 0 -> ashr x, 31   -> all ones if signed
+  if (const VectorType *VTy = dyn_cast<VectorType>(DestTy)) {
+  ICmpInst::Predicate Pred; Value *CmpLHS;
+  if (match(Src, m_ICmp(Pred, m_Value(CmpLHS), m_Zero()))) {
+    if (Pred == ICmpInst::ICMP_SLT && CmpLHS->getType() == DestTy) {
+      const Type *EltTy = VTy->getElementType();
+
+      // splat the shift constant to a cosntant vector
+      Constant *Sh = ConstantInt::get(EltTy, EltTy->getScalarSizeInBits()-1);
+      std::vector<Constant *> Elts(VTy->getNumElements(), Sh);
+      Constant *VSh = ConstantVector::get(Elts);
+      
+      Value *In = Builder->CreateAShr(CmpLHS, VSh, CmpLHS->getName()+".lobit");
+      return ReplaceInstUsesWith(CI, In);
+    }
+  }
+  }
   
   // If the input is a shl/ashr pair of a same constant, then this is a sign
   // extension from a smaller value.  If we could trust arbitrary bitwidth
diff --git a/test/Transforms/InstCombine/vec_sext.ll b/test/Transforms/InstCombine/vec_sext.ll
new file mode 100644
index 00000000000..d7ab96b9cfd
--- /dev/null
+++ b/test/Transforms/InstCombine/vec_sext.ll
@@ -0,0 +1,22 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+define <4 x i32> @psignd_3(<4 x i32> %a, <4 x i32> %b) nounwind ssp {
+entry:
+  %cmp = icmp slt <4 x i32> %b, zeroinitializer
+  %sext = sext <4 x i1> %cmp to <4 x i32>
+  %sub = sub nsw <4 x i32> zeroinitializer, %a
+  %0 = icmp slt <4 x i32> %sext, zeroinitializer
+  %sext3 = sext <4 x i1> %0 to <4 x i32>
+  %1 = xor <4 x i32> %sext3, <i32 -1, i32 -1, i32 -1, i32 -1>
+  %2 = and <4 x i32> %a, %1
+  %3 = and <4 x i32> %sext3, %sub
+  %cond = or <4 x i32> %2, %3
+  ret <4 x i32> %cond
+
+; CHECK:   ashr <4 x i32> %b, <i32 31, i32 31, i32 31, i32 31>
+; CHECK:   sub nsw <4 x i32> zeroinitializer, %a
+; CHECK:   xor <4 x i32> %b.lobit, <i32 -1, i32 -1, i32 -1, i32 -1>
+; CHECK:   and <4 x i32> %a, %0
+; CHECK:   and <4 x i32> %b.lobit, %sub
+; CHECK:   or <4 x i32> %1, %2
+}