Add partial constant emitting support to WebAssembly RyuJIT backend

Co-authored-by: kg <198130+kg@users.noreply.github.com>

Author: Copilot

src/coreclr/jit/codegenwasm.cpp

@@ -104,6 +104,16 @@ void CodeGen::genCodeForTreeNode(GenTree* treeNode)
             genCodeForLclVar(treeNode->AsLclVar());
             break;
 
+        case GT_CNS_INT:
+        case GT_CNS_DBL:
+        {
+            regNumber targetReg  = treeNode->GetRegNum();
+            var_types targetType = treeNode->TypeGet();
+            genSetRegToConst(targetReg, targetType, treeNode);
+            genProduceReg(treeNode);
+        }
+        break;
+
         case GT_RETURN:
             genReturn(treeNode);
             break;
@@ -347,6 +357,41 @@ void CodeGen::genCodeForShiftOrRotate(GenTreeOp* treeNode)
     genProduceReg(treeNode);
 }
 
+//------------------------------------------------------------------------
+// genSetRegToConst: Generate code to set a register to a constant value.
+//
+// Arguments:
+//    targetReg  - The target register
+//    targetType - The type of the target register
+//    tree       - The constant tree node
+//
+void CodeGen::genSetRegToConst(regNumber targetReg, var_types targetType, GenTree* tree)
+{
+    switch (tree->gtOper)
+    {
+        case GT_CNS_INT:
+        {
+            ssize_t constant = tree->AsIntCon()->IconValue();
+            emitAttr encodedSize = (emitAttr)GetEmitter()->emitEncodeLEB64(nullptr, &constant, true);
+            GetEmitter()->emitIns_R_I((targetType == TYP_INT) ? INS_i32_const : INS_i64_const, 
+                                      encodedSize, targetReg, constant);
+        }
+        break;
+
+        case GT_CNS_DBL:
+        {
+            double constant = tree->AsDblCon()->DconValue();
+            emitAttr encodedSize = (targetType == TYP_FLOAT) ? EA_4BYTE : EA_8BYTE;
+            GetEmitter()->emitIns_R_F((targetType == TYP_FLOAT) ? INS_f32_const : INS_f64_const, 
+                                      encodedSize, targetReg, constant);
+        }
+        break;
+
+        default:
+            unreached();
+    }
+}
+
 //------------------------------------------------------------------------
 // genCodeForLclVar: Produce code for a GT_LCL_VAR node.
 //

src/coreclr/jit/emitfmtswasm.h

@@ -29,6 +29,9 @@ enum ID_OPS
 IF_DEF(NONE,    IS_NONE, NONE)
 IF_DEF(OPCODE,  IS_NONE, NONE) // <opcode>
 IF_DEF(ULEB128, IS_NONE, NONE) // <opcode> <ULEB128 immediate>
+IF_DEF(LEB128,  IS_NONE, NONE) // <opcode> <LEB128 immediate (signed)>
+IF_DEF(F32,     IS_NONE, NONE) // <opcode> <f32 immediate>
+IF_DEF(F64,     IS_NONE, NONE) // <opcode> <f64 immediate>
 IF_DEF(MEMARG,  IS_NONE, NONE) // <opcode> <memarg> (<align> <offset>)
 
 #undef IF_DEF

src/coreclr/jit/emitwasm.cpp

@@ -70,6 +70,11 @@ void emitter::emitIns_R_I(instruction ins, emitAttr attr, regNumber reg, ssize_t
     NYI_WASM("emitIns_R_I");
 }
 
+void emitter::emitIns_R_F(instruction ins, emitAttr attr, regNumber reg, double immDbl)
+{
+    NYI_WASM("emitIns_R_F");
+}
+
 void emitter::emitIns_Mov(instruction ins, emitAttr attr, regNumber dstReg, regNumber srcReg, bool canSkip)
 {
     NYI_WASM("emitIns_Mov");
@@ -91,6 +96,12 @@ bool emitter::emitInsIsStore(instruction ins)
     return false;
 }
 
+size_t emitter::emitEncodeLEB64(uint8_t* destination, const void* source, bool valueIsSigned)
+{
+    NYI_WASM("emitEncodeLEB64");
+    return 0;
+}
+
 emitter::insFormat emitter::emitInsFormat(instruction ins)
 {
     // clang-format off

src/coreclr/jit/emitwasm.h

@@ -22,6 +22,7 @@ void emitIns_S(instruction ins, emitAttr attr, int varx, int offs);
 void emitIns_R(instruction ins, emitAttr attr, regNumber reg);
 
 void emitIns_R_I(instruction ins, emitAttr attr, regNumber reg, ssize_t imm);
+void emitIns_R_F(instruction ins, emitAttr attr, regNumber reg, double immDbl);
 void emitIns_Mov(instruction ins, emitAttr attr, regNumber dstReg, regNumber srcReg, bool canSkip);
 void emitIns_R_R(instruction ins, emitAttr attr, regNumber reg1, regNumber reg2);
 
@@ -51,3 +52,5 @@ instrDesc* emitNewInstrCallInd(int              argCnt,
 bool emitInsIsStore(instruction ins);
 
 insFormat emitInsFormat(instruction ins);
+
+size_t emitEncodeLEB64(uint8_t* destination, const void* source, bool valueIsSigned);

src/coreclr/jit/instrswasm.h

@@ -33,11 +33,11 @@ INST(i64_load,    "i64.load",    0, IF_MEMARG,  0x29)
 INST(f32_load,    "f32.load",    0, IF_MEMARG,  0x2A)
 INST(f64_load,    "f64.load",    0, IF_MEMARG,  0x2B)
 // 5.4.7 Numeric Instructions
-// TODO-WASM: Constants
-// INST(i32_const,   "i32.const",   0, IF_LEB128, 0x41)
-// INST(i64_const,   "i64.const",   0, IF_LEB128, 0x42)
-// INST(f32_const,   "f32.const",   0, IF_F32, 0x43)
-// INST(f64_const,   "f64.const",   0, IF_F64, 0x44)
+// Constants
+INST(i32_const,   "i32.const",   0, IF_LEB128,  0x41)
+INST(i64_const,   "i64.const",   0, IF_LEB128,  0x42)
+INST(f32_const,   "f32.const",   0, IF_F32,     0x43)
+INST(f64_const,   "f64.const",   0, IF_F64,     0x44)
 // Integer comparisons
 INST(i32_eqz,     "i32.eqz",     0, IF_OPCODE,  0x45)
 INST(i32_eq,      "i32.eq",      0, IF_OPCODE,  0x46)