Fix PR7174, a couple o Mips fixes:

- Fix a typo for PIC check during jmp table lowering
- Also fix the "first jump table basic block is not
considered only reachable by fall through" problem, use this
ad-hoc solution until I come up with something better.

Patch by stetorvs@gmail.com

llvm-svn: 108820

llvm/lib/Target/Mips/AsmPrinter/MipsAsmPrinter.cpp

@@ -18,6 +18,8 @@
 #include "MipsInstrInfo.h"
 #include "MipsTargetMachine.h"
 #include "MipsMachineFunction.h"
+#include "llvm/BasicBlock.h"
+#include "llvm/Instructions.h"
 #include "llvm/CodeGen/AsmPrinter.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineConstantPool.h"
@@ -75,6 +77,7 @@ namespace {
     }
     virtual void EmitFunctionBodyStart();
     virtual void EmitFunctionBodyEnd();
+    virtual bool isBlockOnlyReachableByFallthrough(const MachineBasicBlock *MBB) const;
     static const char *getRegisterName(unsigned RegNo);
 
     virtual void EmitFunctionEntryLabel();
@@ -227,6 +230,23 @@ void MipsAsmPrinter::EmitFunctionBodyEnd() {
 }
 
 
+/// isBlockOnlyReachableByFallthough - Return true if the basic block has
+/// exactly one predecessor and the control transfer mechanism between
+/// the predecessor and this block is a fall-through.
+bool MipsAsmPrinter::isBlockOnlyReachableByFallthrough(const MachineBasicBlock *MBB) 
+    const {
+  // The predecessor has to be immediately before this block.
+  const MachineBasicBlock *Pred = *MBB->pred_begin();
+
+  // If the predecessor is a switch statement, assume a jump table
+  // implementation, so it is not a fall through.
+  if (const BasicBlock *bb = Pred->getBasicBlock())
+    if (isa<SwitchInst>(bb->getTerminator()))
+      return false;
+  
+  return AsmPrinter::isBlockOnlyReachableByFallthrough(MBB);
+}
+
 // Print out an operand for an inline asm expression.
 bool MipsAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNo, 
                                      unsigned AsmVariant,const char *ExtraCode,

llvm/lib/Target/Mips/MipsISelLowering.cpp

@@ -542,7 +542,7 @@ LowerJumpTable(SDValue Op, SelectionDAG &DAG) const
 
   SDValue JTI = DAG.getTargetJumpTable(JT->getIndex(), PtrVT, OpFlag);
 
-  if (IsPIC) {
+  if (!IsPIC) {
     SDValue Ops[] = { JTI };
     HiPart = DAG.getNode(MipsISD::Hi, dl, DAG.getVTList(MVT::i32), Ops, 1);
   } else // Emit Load from Global Pointer

llvm/test/CodeGen/Mips/2010-07-20-Switch.ll

@@ -0,0 +1,33 @@
+; RUN: llc < %s -march=mips -relocation-model=static | FileCheck %s
+
+define i32 @main() nounwind readnone {
+entry:
+  %x = alloca i32, align 4                        ; <i32*> [#uses=2]
+  volatile store i32 2, i32* %x, align 4
+  %0 = volatile load i32* %x, align 4             ; <i32> [#uses=1]
+; CHECK: lui $3, %hi($JTI0_0)
+; CHECK: sll $2, $2, 2
+; CHECK: addiu $3, $3, %lo($JTI0_0)
+  switch i32 %0, label %bb4 [
+    i32 0, label %bb5
+    i32 1, label %bb1
+    i32 2, label %bb2
+    i32 3, label %bb3
+  ]
+
+bb1:                                              ; preds = %entry
+  ret i32 2
+
+; CHECK: $BB0_2
+bb2:                                              ; preds = %entry
+  ret i32 0
+
+bb3:                                              ; preds = %entry
+  ret i32 3
+
+bb4:                                              ; preds = %entry
+  ret i32 4
+
+bb5:                                              ; preds = %entry
+  ret i32 1
+}