[llvm] [AMDGPU] Introduce "amdgpu-sw-lower-lds" pass to lower LDS accesses to use device global memory. (PR #87265)

[Pierre van Houtryve via llvm-commits]

================
@@ -65,6 +68,219 @@ bool isLDSVariableToLower(const GlobalVariable &GV) {
   return true;
 }
 
+bool eliminateConstantExprUsesOfLDSFromAllInstructions(Module &M) {
+  // Constants are uniqued within LLVM. A ConstantExpr referring to a LDS
+  // global may have uses from multiple different functions as a result.
+  // This pass specialises LDS variables with respect to the kernel that
+  // allocates them.
+
+  // This is semantically equivalent to (the unimplemented as slow):
+  // for (auto &F : M.functions())
+  //   for (auto &BB : F)
+  //     for (auto &I : BB)
+  //       for (Use &Op : I.operands())
+  //         if (constantExprUsesLDS(Op))
+  //           replaceConstantExprInFunction(I, Op);
+
+  SmallVector<Constant *> LDSGlobals;
+  for (auto &GV : M.globals())
+    if (AMDGPU::isLDSVariableToLower(GV))
+      LDSGlobals.push_back(&GV);
+  return convertUsersOfConstantsToInstructions(LDSGlobals);
+}
+
+void getUsesOfLDSByFunction(CallGraph const &CG, Module &M,
+                            FunctionVariableMap &kernels,
+                            FunctionVariableMap &functions) {
+  // Get uses from the current function, excluding uses by called functions
+  // Two output variables to avoid walking the globals list twice
+  for (auto &GV : M.globals()) {
+    if (!AMDGPU::isLDSVariableToLower(GV)) {
+      continue;
+    }
----------------
Pierre-vh wrote:

```suggestion
    if (!AMDGPU::isLDSVariableToLower(GV))
      continue;
```

https://github.com/llvm/llvm-project/pull/87265