Backend: Add optimization for negative modifier

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@intel.com>
Reviewed-by: Pan Xiuli <xiuli.pan@intel.com>

1 files changed, 28 insertions, 4 deletions

diff --git a/backend/src/backend/gen_insn_selection_optimize.cpp b/backend/src/backend/gen_insn_selection_optimize.cpp
index d2e0fb9b..07547ec4 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 +159,13 @@ 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)
       return;
@@ -249,10 +254,29 @@ 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) {