From: Chris Lattner <sabre@nondot.org>
Date: Wed, 14 Dec 2005 19:05:06 +0000 (+0000)
Subject: Fix the (zext (zextload)) case to trigger, similarly for sign extends.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=ad25d4e2df3fe01541d62ab0fd22c7de22ce3a42;p=oota-llvm.git

Fix the (zext (zextload)) case to trigger, similarly for sign extends.
Allow (zext (truncate)) to apply after legalize if the target supports
AND (which all do).

This compiles
short %foo() {
        %tmp.0 = load ubyte* %X         ; <ubyte> [#uses=1]
        %tmp.3 = cast ubyte %tmp.0 to short             ; <short> [#uses=1]
        ret short %tmp.3
}

to:
_foo:
        movzbl _X, %eax
        ret

instead of:

_foo:
        movzbl _X, %eax
        movzbl %al, %eax
        ret

thanks to Evan for pointing this out.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@24709 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index c7cc6916ab9..8077709c94a 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1543,9 +1543,6 @@ SDOperand DAGCombiner::visitSIGN_EXTEND(SDNode *N) {
   // fold (sext (sext x)) -> (sext x)
   if (N0.getOpcode() == ISD::SIGN_EXTEND)
     return DAG.getNode(ISD::SIGN_EXTEND, VT, N0.getOperand(0));
-  // fold (sext (sextload x)) -> (sextload x)
-  if (N0.getOpcode() == ISD::SEXTLOAD && VT == N0.getValueType())
-    return N0;
   // fold (sext (truncate x)) -> (sextinreg x) iff x size == sext size.
   if (N0.getOpcode() == ISD::TRUNCATE && N0.getOperand(0).getValueType() == VT&&
       (!AfterLegalize || 
@@ -1562,6 +1559,20 @@ SDOperand DAGCombiner::visitSIGN_EXTEND(SDNode *N) {
               ExtLoad.getValue(1));
     return SDOperand();
   }
+
+  // fold (sext (sextload x)) -> (sext (truncate (sextload x)))
+  // fold (sext ( extload x)) -> (sext (truncate (sextload x)))
+  if ((N0.getOpcode() == ISD::SEXTLOAD || N0.getOpcode() == ISD::EXTLOAD) &&
+      N0.hasOneUse()) {
+    SDOperand ExtLoad = DAG.getNode(ISD::SEXTLOAD, VT, N0.getOperand(0),
+                                    N0.getOperand(1), N0.getOperand(2),
+                                    N0.getOperand(3));
+    WorkList.push_back(N);
+    CombineTo(N0.Val, DAG.getNode(ISD::TRUNCATE, N0.getValueType(), ExtLoad),
+              ExtLoad.getValue(1));
+    return SDOperand();
+  }
+  
   return SDOperand();
 }
 
@@ -1576,12 +1587,9 @@ SDOperand DAGCombiner::visitZERO_EXTEND(SDNode *N) {
   // fold (zext (zext x)) -> (zext x)
   if (N0.getOpcode() == ISD::ZERO_EXTEND)
     return DAG.getNode(ISD::ZERO_EXTEND, VT, N0.getOperand(0));
-  // fold (zext (zextload x)) -> (zextload x)
-  if (N0.getOpcode() == ISD::ZEXTLOAD && VT == N0.getValueType())
-    return N0;
   // fold (zext (truncate x)) -> (zextinreg x) iff x size == zext size.
   if (N0.getOpcode() == ISD::TRUNCATE && N0.getOperand(0).getValueType() == VT&&
-      !AfterLegalize)
+      (!AfterLegalize || TLI.isOperationLegal(ISD::AND, N0.getValueType())))
     return DAG.getZeroExtendInReg(N0.getOperand(0), N0.getValueType());
   // fold (zext (load x)) -> (zext (truncate (zextload x)))
   if (N0.getOpcode() == ISD::LOAD && N0.hasOneUse()) {
@@ -1593,6 +1601,19 @@ SDOperand DAGCombiner::visitZERO_EXTEND(SDNode *N) {
               ExtLoad.getValue(1));
     return SDOperand();
   }
+
+  // fold (zext (zextload x)) -> (zext (truncate (zextload x)))
+  // fold (zext ( extload x)) -> (zext (truncate (zextload x)))
+  if ((N0.getOpcode() == ISD::ZEXTLOAD || N0.getOpcode() == ISD::EXTLOAD) &&
+      N0.hasOneUse()) {
+    SDOperand ExtLoad = DAG.getNode(ISD::ZEXTLOAD, VT, N0.getOperand(0),
+                                    N0.getOperand(1), N0.getOperand(2),
+                                    N0.getOperand(3));
+    WorkList.push_back(N);
+    CombineTo(N0.Val, DAG.getNode(ISD::TRUNCATE, N0.getValueType(), ExtLoad),
+              ExtLoad.getValue(1));
+    return SDOperand();
+  }
   return SDOperand();
 }