From c02780eed1f78130e8ebff3c3800fcbb1cc79cfd Mon Sep 17 00:00:00 2001
From: Duraid Madina <duraid@octopus.com.au>
Date: Wed, 13 Apr 2005 04:50:54 +0000
Subject: [PATCH] * if ANDing with a constant of the form:

  0x00000..00FFF..FF
      ^      ^
      ^      ^
    any number of
    0's followed by
    some number of
    1's

    then we use dep.z to just paste zeros over the input. For the special
    cases where this is zxt1/zxt2/zxt4, we use those instructions instead,
    because we're all about readability!!!
    that's what it's about!! readability!

  *twitch* ;D


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21279 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/IA64/IA64ISelPattern.cpp | 47 +++++++++++++++++++++++++++--
 1 file changed, 45 insertions(+), 2 deletions(-)

diff --git a/lib/Target/IA64/IA64ISelPattern.cpp b/lib/Target/IA64/IA64ISelPattern.cpp
index c2623d020cf..c501fa1c331 100644
--- a/lib/Target/IA64/IA64ISelPattern.cpp
+++ b/lib/Target/IA64/IA64ISelPattern.cpp
@@ -445,7 +445,7 @@ void ISel::InstructionSelectBasicBlock(SelectionDAG &DAG) {
 
 /// ExactLog2 - This function solves for (Val == 1 << (N-1)) and returns N.  It
 /// returns zero when the input is not exactly a power of two.
-static uint64_t ExactLog2(uint64_t Val) {
+static unsigned ExactLog2(uint64_t Val) {
   if (Val == 0 || (Val & (Val-1))) return 0;
   unsigned Count = 0;
   while (Val != 1) {
@@ -455,6 +455,17 @@ static uint64_t ExactLog2(uint64_t Val) {
   return Count;
 }
 
+/// ExactLog2sub1 - This function solves for (Val == (1 << (N-1))-1)
+/// and returns N.  It returns 666 if Val is not 2^n -1 for some n.
+static unsigned ExactLog2sub1(uint64_t Val) {
+  unsigned int n;
+  for(n=0; n<64; n++) {
+    if(Val==(uint64_t)((1<<n)-1))
+      return n;
+  }
+  return 666;
+}
+
 /// ponderIntegerDivisionBy - When handling integer divides, if the divide
 /// is by a constant such that we can efficiently codegen it, this
 /// function says what to do. Currently, it returns 0 if the division must
@@ -474,6 +485,19 @@ static unsigned ponderIntegerDivisionBy(SDOperand N, bool isSigned,
   return 0; // fallthrough
 }
 
+static unsigned ponderIntegerAndWith(SDOperand N, unsigned& Imm) {
+  if (N.getOpcode() != ISD::Constant) return 0; // if not ANDing with
+                                                // a constant, give up.
+
+  int64_t v = (int64_t)cast<ConstantSDNode>(N)->getSignExtended();
+
+  if ((Imm = ExactLog2sub1(v))!=666) { // if ANDing with ((2^n)-1) for some n
+    return 1; // say so
+  } 
+  
+  return 0; // fallthrough
+}
+
 static unsigned ponderIntegerAdditionWith(SDOperand N, unsigned& Imm) {
   if (N.getOpcode() != ISD::Constant) return 0; // if not adding a
                                                 // constant, give up.
@@ -967,15 +991,34 @@ assert(0 && "hmm, ISD::SIGN_EXTEND: shouldn't ever be reached. bad luck!\n");
 	.addReg(bogusTemp1).addReg(IA64::r0).addReg(IA64::r0).addReg(pTemp);
       break;
     }
+    
     // if not a bool, we just AND away:
     case MVT::i8:
     case MVT::i16:
     case MVT::i32:
     case MVT::i64: {
       Tmp1 = SelectExpr(N.getOperand(0));
+      switch (ponderIntegerAndWith(N.getOperand(1), Tmp3)) {
+        case 1: // ANDing a constant that is 2^n-1 for some n
+	  switch (Tmp3) {
+	    case 8:  // if AND 0x00000000000000FF, be quaint and use zxt1
+	      BuildMI(BB, IA64::ZXT1, 1, Result).addReg(Tmp1);
+	      break;
+	    case 16: // if AND 0x000000000000FFFF, be quaint and use zxt2
+	      BuildMI(BB, IA64::ZXT2, 1, Result).addReg(Tmp1);
+	      break;
+	    case 32: // if AND 0x00000000FFFFFFFF, be quaint and use zxt4
+	      BuildMI(BB, IA64::ZXT4, 1, Result).addReg(Tmp1);
+	      break;
+	    default: // otherwise, use dep.z to paste zeros
+	      BuildMI(BB, IA64::DEPZ, 3, Result).addReg(Tmp1)
+		.addImm(0).addImm(Tmp3);
+	      break;
+	  }
+	  return Result; // early exit
+      } // fallthrough and emit a simple AND:
       Tmp2 = SelectExpr(N.getOperand(1));
       BuildMI(BB, IA64::AND, 2, Result).addReg(Tmp1).addReg(Tmp2);
-      break;
     }
     }
     return Result;