Deduplicate constant data tables

A constant data is assigned to different variables several times, then
we will create multiple globalVariables, which causes the constant data
is repeated in the .rodata section with different names.
Like this:
.rodata (size = 1344 bytes)
    __unnamed_3 (offset = 0  size = 448 hash = 0xB186021131D03E38)
     (offset = 0  size = 0 hash = 0x071E967D705FB008)
          0:3F1FE7C0 3F0B1A4C 3F53F141 00000000 BE095BFF BF71E3A8 3F745048 00000000
         32:3EC6833C BEDE978D 3F1520B0 00000000 3DF8572A BE45729B 3E693F29 00000000
         ...
    __unnamed_2 (offset = 448  size = 448 hash = 0xB186021131D03E38)
        448:3F1FE7C0 3F0B1A4C 3F53F141 00000000 BE095BFF BF71E3A8 3F745048 00000000
        480:3EC6833C BEDE978D 3F1520B0 00000000 3DF8572A BE45729B 3E693F29 00000000
        ...
    __unnamed_1 (offset = 896  size = 448 hash = 0xB186021131D03E38)
        896:3F1FE7C0 3F0B1A4C 3F53F141 00000000 BE095BFF BF71E3A8 3F745048 00000000
        928:3EC6833C BEDE978D 3F1520B0 00000000 3DF8572A BE45729B 3E693F29 00000000
        ...

For the globalVariable that the initialization values are the same, we
should treat them as the same variable.

llpc/lower/llpcSpirvLowerConstImmediateStore.cpp

@@ -222,10 +222,16 @@ bool SpirvLowerConstImmediateStore::tryProcessAlloca(AllocaInst *allocaInst) {
   }
 
   // Step 3: Create the global variable and replace the alloca
-  auto global = new GlobalVariable(*m_module, allocatedTy,
-                                   true, // isConstant
-                                   GlobalValue::InternalLinkage, initializer, "", nullptr, GlobalValue::NotThreadLocal,
-                                   SPIRAS_Constant);
+  GlobalVariable *global = nullptr;
+  auto iter = m_allocToGlobals.find(initializer);
+  if (iter == m_allocToGlobals.end()) {
+    global = new GlobalVariable(*m_module, allocatedTy,
+                                true, // isConstant
+                                GlobalValue::InternalLinkage, initializer, "", nullptr, GlobalValue::NotThreadLocal,
+                                SPIRAS_Constant);
+    m_allocToGlobals[initializer] = global;
+  } else
+    global = iter->second;
   global->takeName(allocaInst);
 
   for (Use &use : llvm::make_early_inc_range(allocaInst->uses()))

llpc/lower/llpcSpirvLowerConstImmediateStore.h

@@ -51,6 +51,8 @@ class SpirvLowerConstImmediateStore : public SpirvLower, public llvm::PassInfoMi
 private:
   bool processAllocaInsts(llvm::Function *func);
   bool tryProcessAlloca(llvm::AllocaInst *allocaInst);
+
+  std::unordered_map<llvm::Value *, llvm::GlobalVariable *> m_allocToGlobals;
 };
 
 } // namespace Llpc