[Beignet] [PATCH 1/2] Backend: Add optimization for negtive modifier

[rander.wang]

         LLVM transform Mad(a, -b, c) to
         Add b, -b, 0
         Mad val, a, b, c

         pow(a,-b) and other buildin math function to the same instruction sequence like above

         for Gen support negtive modifier, mad(a, -b, c) is native suppoted.
         Do it just like a:  mov b, -b, so it is a Mov operation like LocalCopyPropagation

Signed-off-by: rander.wang <rander.wang at intel.com>
---
 .../src/backend/gen_insn_selection_optimize.cpp    | 35 +++++++++++++++++++---
 1 file changed, 31 insertions(+), 4 deletions(-)

diff --git a/backend/src/backend/gen_insn_selection_optimize.cpp b/backend/src/backend/gen_insn_selection_optimize.cpp
index 512a5bd..d1c302d 100644
--- a/backend/src/backend/gen_insn_selection_optimize.cpp
+++ b/backend/src/backend/gen_insn_selection_optimize.cpp
@@ -74,8 +74,7 @@ namespace gbe
                   const GenRegister& replacement) :
                   insn(insn), intermedia(intermedia), replacement(replacement)
       {
-        assert(insn.opcode == SEL_OP_MOV);
-        assert(&(insn.src(0)) == &replacement);
+        assert(insn.opcode == SEL_OP_MOV || insn.opcode == SEL_OP_ADD);
         assert(&(insn.dst(0)) == &intermedia);
         this->elements = CalculateElements(intermedia, insn.state.execWidth);
         replacementOverwritten = false;
@@ -102,6 +101,7 @@ namespace gbe
     void doReplacement(ReplaceInfo* info);
     bool CanBeReplaced(const ReplaceInfo* info, const SelectionInstruction& insn, const GenRegister& var);
     void cleanReplaceInfoMap();
+    void doNegAddOptimization(SelectionInstruction& insn);
 
     SelectionBlock &bb;
     const ir::Liveness::LiveOut& liveout;
@@ -159,8 +159,14 @@ namespace gbe
 
   void SelBasicBlockOptimizer::addToReplaceInfoMap(SelectionInstruction& insn)
   {
-    assert(insn.opcode == SEL_OP_MOV);
-    const GenRegister& src = insn.src(0);
+    assert(insn.opcode == SEL_OP_MOV || insn.opcode == SEL_OP_ADD);
+    GenRegister& src = insn.src(0);
+    if(insn.opcode == SEL_OP_ADD)
+    {
+      if(src.file == GEN_IMMEDIATE_VALUE)
+        src = insn.src(1);
+    }
+
     const GenRegister& dst = insn.dst(0);
     if (src.type != dst.type || src.file != dst.file || src.hstride != dst.hstride)
       return;
@@ -246,10 +252,31 @@ namespace gbe
 
       if (insn.opcode == SEL_OP_MOV)
         addToReplaceInfoMap(insn);
+
+      doNegAddOptimization(insn);
     }
     cleanReplaceInfoMap();
   }
 
+  /* LLVM transform Mad(a, -b, c) to
+     Add b, -b, 0
+     Mad val, a, b, c
+     for Gen support negtive modifier, mad(a, -b, c) is native suppoted.
+     Also it can be used for the same like instruction sequence.
+     Do it just like a:  mov b, -b, so it is a Mov operation like LocalCopyPropagation
+  */
+  void SelBasicBlockOptimizer::doNegAddOptimization(SelectionInstruction& insn)
+  {
+      if(insn.opcode == SEL_OP_ADD)
+      {
+          GenRegister src0 = insn.src(0);
+          GenRegister src1 = insn.src(1);
+          if((src0.negation && src1.file == GEN_IMMEDIATE_VALUE && src1.value.f == 0.0f) ||
+              (src1.negation && src0.file == GEN_IMMEDIATE_VALUE && src0.value.f == 0.0f))
+              addToReplaceInfoMap(insn);
+      }
+  }
+
   void SelBasicBlockOptimizer::run()
   {
     for (size_t i = 0; i < MaxTries; ++i) {
-- 
2.7.4