[llvm] [SandboxIR] Implement the InsertElementInst class (PR #102404)

[via llvm-commits]

================
@@ -630,6 +630,44 @@ define void @foo(i1 %c0, i8 %v0, i8 %v1, i1 %c1) {
   }
 }
 
+TEST_F(SandboxIRTest, InsertElementInst) {
+  parseIR(C, R"IR(
+define void @foo(i8 %v0, i8 %v1) {
+  %ins0 = insertelement <2 x i8> poison, i8 %v0, i32 0
+  %ins1 = insertelement <2 x i8> %ins0, i8 %v1, i32 1
+  ret void
+}
+)IR");
+  Function &F = *M->getFunction("foo");
+  sandboxir::Context Ctx(C);
+  auto &SBF = *Ctx.createFunction(&F);
+  unsigned ArgIdx = 0;
+  auto *Arg0 = SBF.getArg(ArgIdx++);
+  auto *Arg1 = SBF.getArg(ArgIdx++);
+  auto *SBB = &*SBF.begin();
+  auto It = SBB->begin();
+  auto *Ins0 = cast<sandboxir::InsertElementInst>(&*It++);
+  auto *Ins1 = cast<sandboxir::InsertElementInst>(&*It++);
+  auto *Ret = &*It++;
+
+  EXPECT_EQ(Ins0->getOpcode(), sandboxir::Instruction::Opcode::InsertElement);
+  EXPECT_EQ(Ins0->getOperand(1), Arg0);
+  EXPECT_EQ(Ins1->getOperand(1), Arg1);
+  EXPECT_EQ(Ins1->getOperand(0), Ins0);
+  auto *Poison = Ins0->getOperand(0);
+  auto *Idx = Ins0->getOperand(2);
+  auto *NewI1 =
+      cast<sandboxir::InsertElementInst>(sandboxir::InsertElementInst::create(
+          Poison, Arg0, Idx, Ret, Ctx, "NewIns1"));
+  EXPECT_EQ(NewI1->getOperand(0), Poison);
+  EXPECT_EQ(NewI1->getNextNode(), Ret);
+
+  auto *NewI2 =
+      cast<sandboxir::InsertElementInst>(sandboxir::InsertElementInst::create(
+          Poison, Arg0, Idx, SBB, Ctx, "NewIns2"));
+  EXPECT_EQ(NewI2->getPrevNode(), Ret);
+}
----------------
vporpo wrote:

For the `isValidOperands()` check I would add an extra `%vec` argument to `define void @foo(i8 %v0, i8 %v1, <2 x i8> %vec)` auto *ArgVec = F.getArg(ArgIdx++);

Then we would need to get both the sandboxir and the llvm arguments:
```
unsigned LLVMArgIdx = 0;
auto *LLVMArg0 = LLVMF.getArg(LLVMArgIdx++);
auto *LLVMArg1 = LLVMF.getArg(LLVMArgIdx++);
auto *LLVMArgVec = LLVMF.getArg(LLVMArgIdx++);
...
auto *Arg1 = F.getArg(ArgIdx++);
auto *ArgVec = F.getArg(ArgIdx++);

```

Then:
```
auto *Zero = sandboxir::Constant::createInt(Type::getInt8Ty(C), 0, Ctx);
auto *LLVMZero = llvm::Constant::getZero(Type::getInt8Ty(C));
```

Finally I would add a check like: 
```
EXPECT_EQ(sandboxir::InsertElementInst::isValidOperands(ArgVec, Arg0, Zero), llvm::InsertElementInst::isValidOperands(LLVMArgVec, LLVMArg0, LLVMZero));
```
To make sure we exercise this even more we can also try swapping the arguments:
```
EXPECT_EQ(sandboxir::InsertElementInst::isValidOperands(Arg0, ArgVec, Zero), llvm::InsertElementInst::isValidOperands(LLVMArg0, LLVMArgVec, LLVMZero));
```

https://github.com/llvm/llvm-project/pull/102404