[llvm] [SandboxIR] Add utility function to find the base Value for Mem instructions (PR #112030)

[via llvm-commits]

================
@@ -215,3 +215,35 @@ define void @foo(float %arg0, double %arg1, i8 %arg2, i64 %arg3, ptr %arg4) {
   EXPECT_EQ(sandboxir::Utils::getNumBits(L2), 8u);
   EXPECT_EQ(sandboxir::Utils::getNumBits(L3), 64u);
 }
+
+TEST_F(UtilsTest, GetMemBase) {
+  parseIR(C, R"IR(
+define void @foo(ptr %ptrA, float %val, ptr %ptrB) {
+bb:
+  %gepA0 = getelementptr float, ptr %ptrA, i32 0
+  %gepA1 = getelementptr float, ptr %ptrA, i32 1
+  %gepB0 = getelementptr float, ptr %ptrB, i32 0
+  %gepB1 = getelementptr float, ptr %ptrB, i32 1
+  store float %val, ptr %gepA0
+  store float %val, ptr %gepA1
+  store float %val, ptr %gepB0
+  store float %val, ptr %gepB1
+  ret void
+}
+)IR");
+  llvm::Function &Foo = *M->getFunction("foo");
+  sandboxir::Context Ctx(C);
+  sandboxir::Function *F = Ctx.createFunction(&Foo);
+
+  auto It = std::next(F->begin()->begin(), 4);
+  auto *St0 = cast<sandboxir::StoreInst>(&*It++);
+  auto *St1 = cast<sandboxir::StoreInst>(&*It++);
+  auto *St2 = cast<sandboxir::StoreInst>(&*It++);
+  auto *St3 = cast<sandboxir::StoreInst>(&*It++);
+  EXPECT_EQ(sandboxir::Utils::getMemInstructionBase(St0),
+            sandboxir::Utils::getMemInstructionBase(St1));
+  EXPECT_EQ(sandboxir::Utils::getMemInstructionBase(St2),
+            sandboxir::Utils::getMemInstructionBase(St3));
+  EXPECT_NE(sandboxir::Utils::getMemInstructionBase(St0),
+            sandboxir::Utils::getMemInstructionBase(St3));
----------------
vporpo wrote:

These checks are OK, but we are not actually checking what the returned value actually is.

Some checks like this would also help:
```
EXPECT_EQ(sandboxir::Utils::getMemInsructionBase(St0), Ctx.getValue(LLVMSt0));
```

https://github.com/llvm/llvm-project/pull/112030