From 36ae6c182759871a4af71d9af85f970b29a669f1 Mon Sep 17 00:00:00 2001
From: Bill Wendling <isanbard@gmail.com>
Date: Wed, 4 Mar 2009 00:18:06 +0000
Subject: [PATCH] The DAG combiner was performing a BT combine. The BT combine
 had a value of -1, so it changed it into a 31 via the
 TLO.ShrinkDemandedConstant() call. Then it would go through the DAG combiner
 again. This time it had a value of 31, which was turned into a -1 by
 TLI.SimplifyDemandedBits(). This would ping pong forever.

Teach the TLO.ShrinkDemandedConstant() call not to lower a value if the demanded
value is an XOR of all ones.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@65985 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/SelectionDAG/TargetLowering.cpp | 33 ++++++++++++------
 test/CodeGen/X86/2009-03-03-BTHang.ll       | 37 +++++++++++++++++++++
 2 files changed, 59 insertions(+), 11 deletions(-)
 create mode 100644 test/CodeGen/X86/2009-03-03-BTHang.ll

diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index e92932b186f..7913c019631 100644
--- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -746,23 +746,34 @@ TargetLowering::isOffsetFoldingLegal(const GlobalAddressSDNode *GA) const {
 bool TargetLowering::TargetLoweringOpt::ShrinkDemandedConstant(SDValue Op, 
                                                         const APInt &Demanded) {
   DebugLoc dl = Op.getDebugLoc();
+
   // FIXME: ISD::SELECT, ISD::SELECT_CC
   switch (Op.getOpcode()) {
   default: break;
-  case ISD::AND:
-  case ISD::OR:
   case ISD::XOR:
-    if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Op.getOperand(1)))
-      if (C->getAPIntValue().intersects(~Demanded)) {
-        MVT VT = Op.getValueType();
-        SDValue New = DAG.getNode(Op.getOpcode(), dl, VT, Op.getOperand(0),
-                                    DAG.getConstant(Demanded &
-                                                      C->getAPIntValue(), 
-                                                    VT));
-        return CombineTo(Op, New);
-      }
+  case ISD::AND:
+  case ISD::OR: {
+    ConstantSDNode *C = dyn_cast<ConstantSDNode>(Op.getOperand(1));
+    if (!C) return false;
+
+    if (Op.getOpcode() == ISD::XOR &&
+        (C->getAPIntValue() | (~Demanded)).isAllOnesValue())
+      return false;
+
+    // if we can expand it to have all bits set, do it
+    if (C->getAPIntValue().intersects(~Demanded)) {
+      MVT VT = Op.getValueType();
+      SDValue New = DAG.getNode(Op.getOpcode(), dl, VT, Op.getOperand(0),
+                                DAG.getConstant(Demanded &
+                                                C->getAPIntValue(), 
+                                                VT));
+      return CombineTo(Op, New);
+    }
+
     break;
   }
+  }
+
   return false;
 }
 
diff --git a/test/CodeGen/X86/2009-03-03-BTHang.ll b/test/CodeGen/X86/2009-03-03-BTHang.ll
new file mode 100644
index 00000000000..0f338d8eadf
--- /dev/null
+++ b/test/CodeGen/X86/2009-03-03-BTHang.ll
@@ -0,0 +1,37 @@
+; RUN: llvm-as < %s | llc -march=x86
+; rdar://6642541
+
+ 	%struct.HandleBlock = type { [30 x i32], [990 x i8*], %struct.HandleBlockTrailer }
+ 	%struct.HandleBlockTrailer = type { %struct.HandleBlock* }
+
+define hidden zeroext i8 @IsHandleAllocatedFromPool(i8** %h) nounwind optsize {
+entry:
+	%0 = ptrtoint i8** %h to i32		; <i32> [#uses=2]
+	%1 = and i32 %0, -4096		; <i32> [#uses=1]
+	%2 = inttoptr i32 %1 to %struct.HandleBlock*		; <%struct.HandleBlock*> [#uses=3]
+	%3 = getelementptr %struct.HandleBlock* %2, i32 0, i32 0, i32 0		; <i32*> [#uses=1]
+	%4 = load i32* %3, align 4096		; <i32> [#uses=1]
+	%5 = icmp eq i32 %4, 1751280747		; <i1> [#uses=1]
+	br i1 %5, label %bb, label %bb1
+
+bb:		; preds = %entry
+	%6 = getelementptr %struct.HandleBlock* %2, i32 0, i32 1		; <[990 x i8*]*> [#uses=1]
+	%7 = ptrtoint [990 x i8*]* %6 to i32		; <i32> [#uses=1]
+	%8 = sub i32 %0, %7		; <i32> [#uses=2]
+	%9 = lshr i32 %8, 2		; <i32> [#uses=1]
+	%10 = ashr i32 %8, 7		; <i32> [#uses=1]
+	%11 = and i32 %10, 134217727		; <i32> [#uses=1]
+	%12 = getelementptr %struct.HandleBlock* %2, i32 0, i32 0, i32 %11		; <i32*> [#uses=1]
+	%not.i = and i32 %9, 31		; <i32> [#uses=1]
+	%13 = xor i32 %not.i, 31		; <i32> [#uses=1]
+	%14 = shl i32 1, %13		; <i32> [#uses=1]
+	%15 = load i32* %12, align 4		; <i32> [#uses=1]
+	%16 = and i32 %15, %14		; <i32> [#uses=1]
+	%17 = icmp eq i32 %16, 0		; <i1> [#uses=1]
+	%tmp = zext i1 %17 to i8		; <i8> [#uses=1]
+	ret i8 %tmp
+
+bb1:		; preds = %entry
+	ret i8 0
+}
+
-- 
2.34.1