[Beignet] [PATCH] GBE: Handle empty basicblock in Instruction selection

[Ruiling Song]

I meet a corner case which leads to empty bb.

Lable $12
add %3, %2, 1

and what's more %3 is not used anymore later, so we will not select
instruction for this line of code. Then only Label instruction left
in the bb, which leads to wrong endifLabel used. The fix simply
generate endif instruction if needed at first in matchBasicBlock().

Signed-off-by: Ruiling Song <ruiling.song at intel.com>
---
 backend/src/backend/gen_insn_selection.cpp |   19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/backend/src/backend/gen_insn_selection.cpp b/backend/src/backend/gen_insn_selection.cpp
index ecb64cd..77d3177 100644
--- a/backend/src/backend/gen_insn_selection.cpp
+++ b/backend/src/backend/gen_insn_selection.cpp
@@ -402,7 +402,7 @@ namespace gbe
     /*! Build a DAG for the basic block (return number of instructions) */
     uint32_t buildBasicBlockDAG(const ir::BasicBlock &bb);
     /*! Perform the selection on the basic block */
-    void matchBasicBlock(uint32_t insnNum);
+    void matchBasicBlock(const ir::BasicBlock &bb, uint32_t insnNum);
     /*! A root instruction needs to be generated */
     bool isRoot(const ir::Instruction &insn) const;
 
@@ -1530,10 +1530,16 @@ namespace gbe
     return insnNum;
   }
 
-  void Selection::Opaque::matchBasicBlock(uint32_t insnNum)
+  void Selection::Opaque::matchBasicBlock(const ir::BasicBlock &bb, uint32_t insnNum)
   {
     // Bottom up code generation
     bool needEndif = this->block->hasBranch == false && !this->block->hasBarrier;
+
+    if(needEndif) {
+      const ir::BasicBlock *next = bb.getNextBlock();
+      this->ENDIF(GenRegister::immd(0), next->getLabelIndex());
+    }
+
     for (int32_t insnID = insnNum-1; insnID >= 0; --insnID) {
       // Process all possible patterns for this instruction
       SelectionDAG &dag = *insnDAG[insnID];
@@ -1570,13 +1576,6 @@ namespace gbe
           this->block->isLargeBlock = true;
         }
 
-        if (needEndif) {
-          const ir::BasicBlock *curr = insn.getParent();
-          const ir::BasicBlock *next = curr->getNextBlock();
-          this->ENDIF(GenRegister::immd(0), next->getLabelIndex());
-          needEndif = false;
-        }
-
         // Output the code in the current basic block
         this->endBackwardGeneration();
       }
@@ -1593,7 +1592,7 @@ namespace gbe
       this->dagPool.rewind();
       this->appendBlock(bb);
       const uint32_t insnNum = this->buildBasicBlockDAG(bb);
-      this->matchBasicBlock(insnNum);
+      this->matchBasicBlock(bb, insnNum);
     });
    }
 
-- 
1.7.10.4