[CFG]增加分支优化，为SCCP调用做铺垫，预备修改phi定义

src/SysYIRCFGOpt.cpp

@@ -476,4 +476,90 @@ bool SysYCFGOpt::SysYAddReturn(Function *func, IRBuilder* pBuilder) {
   return changed;
 }
 
+// 条件分支转换为无条件分支
+// 主要针对已知条件值的分支转换为无条件分支
+// 例如 if (cond) { ... } else { ... } 中的 cond 已经
+// 确定为 true 或 false 的情况
+bool SysYCFGOpt::SysYCondBr2Br(Function *func, IRBuilder* pBuilder) {
+  bool changed = false;
+
+  for (auto &basicblock : func->getBasicBlocks()) {
+    if (basicblock->getNumInstructions() == 0)
+      continue;
+    
+    auto thelast = basicblock->getInstructions().end();
+    --thelast;
+
+    if (thelast->get()->isConditional()){
+      ConstantValue *constOperand = dynamic_cast<ConstantValue *>(thelast->get()->getOperand(0));
+      std::string opname;
+      int constint = 0;
+      float constfloat = 0.0F;
+      bool constint_Use = false;
+      bool constfloat_Use = false;
+      if (constOperand != nullptr) {
+        if (constOperand->isFloat()) {
+          constfloat = constOperand->getFloat();
+          constfloat_Use = true;
+        } else {
+          constint = constOperand->getInt();
+          constint_Use = true;
+        }
+      }
+      // 如果可以计算
+      if (constfloat_Use || constint_Use) {
+        changed = true;
+
+        auto thenBlock = dynamic_cast<BasicBlock *>(thelast->get()->getOperand(1));
+        auto elseBlock = dynamic_cast<BasicBlock *>(thelast->get()->getOperand(2));
+        SysYIROptUtils::usedelete(thelast->get());
+        thelast = basicblock->getInstructions().erase(thelast);
+        if ((constfloat_Use && constfloat == 1.0F) || (constint_Use && constint == 1)) {
+
+          pBuilder->setPosition(basicblock.get(), basicblock->end());
+          pBuilder->createUncondBrInst(thenBlock, {});
+          int phiindex = 0;
+          for (auto pred : elseBlock->getPredecessors()) {
+            phiindex++;
+            if (pred == basicblock.get()) {
+              break;
+            }
+          }
+
+          for (auto &phiinst : elseBlock->getInstructions()) {
+            if (phiinst->getKind() != Instruction::kPhi) {
+              break;
+            }
+            phiinst->removeOperand(phiindex);
+          }
+          basicblock->removeSuccessor(elseBlock);
+          elseBlock->removePredecessor(basicblock.get());
+        } else {
+
+          pBuilder->setPosition(basicblock.get(), basicblock->end());
+          pBuilder->createUncondBrInst(elseBlock, {});
+          int phiindex = 0;
+          for (auto pred : thenBlock->getPredecessors()) {
+            phiindex++;
+            if (pred == basicblock.get()) {
+              break;
+            }
+          }
+
+          for (auto &phiinst : thenBlock->getInstructions()) {
+            if (phiinst->getKind() != Instruction::kPhi) {
+              break;
+            }
+            phiinst->removeOperand(phiindex);
+          }
+          basicblock->removeSuccessor(thenBlock);
+          thenBlock->removePredecessor(basicblock.get());
+        }
+      }
+    }
+  }
+
+  return changed;
+}
+
 }  // namespace sysy