[llvm] [SelectionDAG] Add space-optimized forms of OPC_EmitRegister (PR #73291)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-selectiondag

Author: Wang Pengcheng (wangpc-pp)

<details>
<summary>Changes</summary>

The followed byte of `OPC_EmitRegister` is a MVT type, which is
usually i32 or i64.

We add `OPC_EmitRegisterI32` and `OPC_EmitRegisterI64` so that we
can reduce one byte.

Overall this reduces the llc binary size with all in-tree targets by
about 10K.


---
Full diff: https://github.com/llvm/llvm-project/pull/73291.diff


3 Files Affected:

- (modified) llvm/include/llvm/CodeGen/SelectionDAGISel.h (+2) 
- (modified) llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp (+15-3) 
- (modified) llvm/utils/TableGen/DAGISelMatcherEmitter.cpp (+15-3) 


``````````diff
diff --git a/llvm/include/llvm/CodeGen/SelectionDAGISel.h b/llvm/include/llvm/CodeGen/SelectionDAGISel.h
index ffeb4959ba7d076..e05a3e903c28048 100644
--- a/llvm/include/llvm/CodeGen/SelectionDAGISel.h
+++ b/llvm/include/llvm/CodeGen/SelectionDAGISel.h
@@ -161,6 +161,8 @@ class SelectionDAGISel : public MachineFunctionPass {
     OPC_EmitInteger,
     OPC_EmitStringInteger,
     OPC_EmitRegister,
+    OPC_EmitRegisterI32,
+    OPC_EmitRegisterI64,
     OPC_EmitRegister2,
     OPC_EmitConvertToTarget,
     OPC_EmitMergeInputChains,
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 7d9bebdca127224..a5005d74faffeb7 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -3465,9 +3465,21 @@ void SelectionDAGISel::SelectCodeCommon(SDNode *NodeToMatch,
                                                         VT), nullptr));
       continue;
     }
-    case OPC_EmitRegister: {
-      MVT::SimpleValueType VT =
-        (MVT::SimpleValueType)MatcherTable[MatcherIndex++];
+    case OPC_EmitRegister:
+    case OPC_EmitRegisterI32:
+    case OPC_EmitRegisterI64: {
+      MVT::SimpleValueType VT;
+      switch (Opcode) {
+      case OPC_EmitRegisterI32:
+        VT = MVT::i32;
+        break;
+      case OPC_EmitRegisterI64:
+        VT = MVT::i64;
+        break;
+      default:
+        VT = (MVT::SimpleValueType)MatcherTable[MatcherIndex++];
+        break;
+      }
       unsigned RegNo = MatcherTable[MatcherIndex++];
       RecordedNodes.push_back(std::pair<SDValue, SDNode*>(
                               CurDAG->getRegister(RegNo, VT), nullptr));
diff --git a/llvm/utils/TableGen/DAGISelMatcherEmitter.cpp b/llvm/utils/TableGen/DAGISelMatcherEmitter.cpp
index 4a11991036efc11..4f1f4b2512a626c 100644
--- a/llvm/utils/TableGen/DAGISelMatcherEmitter.cpp
+++ b/llvm/utils/TableGen/DAGISelMatcherEmitter.cpp
@@ -687,14 +687,26 @@ EmitMatcher(const Matcher *N, const unsigned Indent, unsigned CurrentIdx,
   case Matcher::EmitRegister: {
     const EmitRegisterMatcher *Matcher = cast<EmitRegisterMatcher>(N);
     const CodeGenRegister *Reg = Matcher->getReg();
+    MVT::SimpleValueType VT = Matcher->getVT();
     // If the enum value of the register is larger than one byte can handle,
     // use EmitRegister2.
     if (Reg && Reg->EnumValue > 255) {
-      OS << "OPC_EmitRegister2, " << getEnumName(Matcher->getVT()) << ", ";
+      OS << "OPC_EmitRegister2, " << getEnumName(VT) << ", ";
       OS << "TARGET_VAL(" << getQualifiedName(Reg->TheDef) << "),\n";
       return 4;
     } else {
-      OS << "OPC_EmitRegister, " << getEnumName(Matcher->getVT()) << ", ";
+      unsigned OpBytes;
+      switch (VT) {
+      case MVT::i32:
+      case MVT::i64:
+        OpBytes = 1;
+        OS << "OPC_EmitRegisterI" << MVT(VT).getScalarSizeInBits() << ", ";
+        break;
+      default:
+        OpBytes = 2;
+        OS << "OPC_EmitRegister, " << getEnumName(VT) << ", ";
+        break;
+      }
       if (Reg) {
         OS << getQualifiedName(Reg->TheDef) << ",\n";
       } else {
@@ -703,7 +715,7 @@ EmitMatcher(const Matcher *N, const unsigned Indent, unsigned CurrentIdx,
           OS << "/*zero_reg*/";
         OS << ",\n";
       }
-      return 3;
+      return OpBytes + 1;
     }
   }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/73291