From 12f52faf934d71e74e204a6b5d86e3d728885ed2 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Tue, 19 Sep 2006 06:18:21 +0000
Subject: [PATCH] implement select.ll:test19-22

llvm-svn: 30482
---
 .../Scalar/InstructionCombining.cpp           | 49 ++++++++++++++++---
 1 file changed, 43 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index 7a3b97783b26..40dfb4163c83 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -5690,12 +5690,48 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
         return new CastInst(NotCond, SI.getType());
       }
 
-      // If one of the constants is zero (we know they can't both be) and we
-      // have a setcc instruction with zero, and we have an 'and' with the
-      // non-constant value, eliminate this whole mess.  This corresponds to
-      // cases like this: ((X & 27) ? 27 : 0)
-      if (TrueValC->isNullValue() || FalseValC->isNullValue())
-        if (SetCondInst *IC = dyn_cast<SetCondInst>(SI.getCondition()))
+      if (SetCondInst *IC = dyn_cast<SetCondInst>(SI.getCondition())) {
+
+        // (x <s 0) ? -1 : 0 -> sra x, 31
+        // (x >u 2147483647) ? -1 : 0 -> sra x, 31
+        if (TrueValC->isAllOnesValue() && FalseValC->isNullValue())
+          if (ConstantInt *CmpCst = dyn_cast<ConstantInt>(IC->getOperand(1))) {
+            bool CanXForm = false;
+            if (CmpCst->getType()->isSigned())
+              CanXForm = CmpCst->isNullValue() && 
+                         IC->getOpcode() == Instruction::SetLT;
+            else {
+              unsigned Bits = CmpCst->getType()->getPrimitiveSizeInBits();
+              CanXForm = (CmpCst->getRawValue() == ~0ULL >> (64-Bits+1)) &&
+                         IC->getOpcode() == Instruction::SetGT;
+            }
+            
+            // The comparison constant and the result are not neccessarily the
+            // same width.  In any case, the first step to do is make sure that
+            // X is signed.
+            Value *X = IC->getOperand(0);
+            if (!X->getType()->isSigned())
+              X = InsertCastBefore(X, X->getType()->getSignedVersion(), SI);
+            
+            // Now that X is signed, we have to make the all ones value.  Do
+            // this by inserting a new SRA.
+            unsigned Bits = X->getType()->getPrimitiveSizeInBits();
+            Constant *ShAmt = ConstantUInt::get(Type::UByteTy, Bits-1);
+            Instruction *SRA = new ShiftInst(Instruction::Shr, X, ShAmt,"ones");
+            InsertNewInstBefore(SRA, SI);
+            
+            // Finally, convert to the type of the select RHS.  If this is
+            // smaller than the compare value, it will truncate the ones to fit.
+            // If it is larger, it will sext the ones to fit.
+            return new CastInst(SRA, SI.getType());
+          }
+
+
+        // If one of the constants is zero (we know they can't both be) and we
+        // have a setcc instruction with zero, and we have an 'and' with the
+        // non-constant value, eliminate this whole mess.  This corresponds to
+        // cases like this: ((X & 27) ? 27 : 0)
+        if (TrueValC->isNullValue() || FalseValC->isNullValue())
           if (IC->isEquality() && isa<ConstantInt>(IC->getOperand(1)) &&
               cast<Constant>(IC->getOperand(1))->isNullValue())
             if (Instruction *ICA = dyn_cast<Instruction>(IC->getOperand(0)))
@@ -5715,6 +5751,7 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
                                   Instruction::Xor, V, ICA->getOperand(1)), SI);
                 return ReplaceInstUsesWith(SI, V);
               }
+      }
     }
 
   // See if we are selecting two values based on a comparison of the two values.