[Beignet] [PATCH 02/18] GBE: Remove BBs if it only has a label instruction.

[Zhigang Gong]

Signed-off-by: Zhigang Gong <zhigang.gong at intel.com>
---
 backend/src/ir/context.cpp  |  3 +-
 backend/src/ir/function.cpp | 75 +++++++++++++++++++++++++++++++++++++++++++++
 backend/src/ir/function.hpp |  4 +++
 3 files changed, 81 insertions(+), 1 deletion(-)

diff --git a/backend/src/ir/context.cpp b/backend/src/ir/context.cpp
index 15d3b0a..0fd6803 100644
--- a/backend/src/ir/context.cpp
+++ b/backend/src/ir/context.cpp
@@ -75,7 +75,8 @@ namespace ir {
     // Remove all returns and insert one unique return block at the end of the
     // function
     lowerReturn(unit, fn->getName());
-
+    // Remove empty labels at first
+    fn->removeEmptyLabels();
     // Properly order labels and compute the CFG, it's needed by FunctionArgumentLower
     fn->sortLabels();
     fn->computeCFG();
diff --git a/backend/src/ir/function.cpp b/backend/src/ir/function.cpp
index a6aecb5..7ea3b1a 100644
--- a/backend/src/ir/function.cpp
+++ b/backend/src/ir/function.cpp
@@ -64,6 +64,81 @@ namespace ir {
     loops.push_back(GBE_NEW(Loop, bbs, exits));
   }
 
+  void Function::removeBlock(BasicBlock *BB) {
+    GBE_ASSERTM(BB->begin() == BB->end(), "BB to be removed is not empty");
+    if (BB->getPrevBlock() != NULL && BB->getNextBlock() != NULL) {
+      BB->getPrevBlock()->nextBlock = BB->getNextBlock();
+      BB->getNextBlock()->prevBlock = BB->getPrevBlock();
+    }
+    for(auto it = blocks.begin(); it != blocks.end(); it++) {
+      if (*it == BB) {
+        blocks.erase(it);
+        break;
+      }
+    }
+  }
+
+  void Function::removeEmptyLabels(void) {
+    // Empty label map, we map the removed label to the next label.
+    map<LabelIndex, LabelIndex> labelMap;
+    map<LabelIndex, LabelIndex> revLabelMap;
+    foreachBlock([&](BasicBlock &BB) {
+      Instruction * insn = BB.getLastInstruction();
+      if (insn->getOpcode() == OP_LABEL) {
+        const LabelIndex index = BB.getLabelIndex();
+        const LabelIndex next = LabelIndex(((uint16_t)index) + 1);
+        labelMap.insert(std::make_pair(index, next));
+        auto needFixIt = revLabelMap.find(index);
+        if (needFixIt != revLabelMap.end()) {
+          // Fix up the previous map with the new next label.
+          labelMap.erase(needFixIt->second);
+          labelMap.insert(std::make_pair(needFixIt->second, next));
+        }
+        revLabelMap.insert(std::make_pair(next, index));
+        insn->remove();
+        removeBlock(&BB);
+      }
+    });
+
+    // fix labels for loops
+    for (auto &x : loops) {
+      for (auto &y : x->bbs) {
+        if (labelMap.find(y) != labelMap.end())
+          y = labelMap.find(y)->second;
+      }
+
+      for (auto &z : x->exits) {
+        if (labelMap.find(z.first) != labelMap.end())
+          z.first = labelMap.find(z.first)->second;
+        if (labelMap.find(z.second) != labelMap.end())
+          z.second = labelMap.find(z.second)->second;
+      }
+    }
+
+
+    // Patch all branch instructions with the new labels
+    foreachInstruction([&](Instruction &insn) {
+      if (insn.getOpcode() != OP_BRA)
+        return;
+
+      // Get the current branch instruction
+      BranchInstruction &bra = cast<BranchInstruction>(insn);
+      const LabelIndex index = bra.getLabelIndex();
+      if (labelMap.find(index) == labelMap.end())
+        return;
+      const LabelIndex newIndex = labelMap.find(index)->second;
+
+      // Insert the patched branch instruction
+      if (bra.isPredicated() == true) {
+        const Instruction newBra = BRA(newIndex, bra.getPredicateIndex());
+        newBra.replace(&insn);
+      } else {
+        const Instruction newBra = BRA(newIndex);
+        newBra.replace(&insn);
+      }
+    });
+  }
+
   void Function::sortLabels(void) {
     uint32_t last = 0;
 
diff --git a/backend/src/ir/function.hpp b/backend/src/ir/function.hpp
index 03aeaeb..ad4773e 100644
--- a/backend/src/ir/function.hpp
+++ b/backend/src/ir/function.hpp
@@ -281,6 +281,10 @@ namespace ir {
     void computeCFG(void);
     /*! Sort labels in increasing orders (top block has the smallest label) */
     void sortLabels(void);
+    /*! Remove empty block. */
+    void removeBlock(BasicBlock *BB);
+    /*! Remove empty Label. */
+    void removeEmptyLabels(void);
     /*! Get the pointer family */
     RegisterFamily getPointerFamily(void) const;
     /*! Number of registers in the register file */
-- 
1.8.3.2