[llvm] [AMDGPU][LowerBufferFatPointers] Fix lack of rewrite when loading/storing null (PR #154128)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-amdgpu

Author: Krzysztof Drewniak (krzysz00)

<details>
<summary>Changes</summary>

Fixes #<!-- -->154056.

The fat buffer lowering pass was erroniously detecting that it did not need to run on functions that only load/store to the null constant (or other such constants). We thought this would be covered by specilaizing constants out to instructions, but that doesn't account foc trivial constants like null. Therefoe, we check the operands of instructions for buffer fat pointers in order to find such constants and ensure the pass runs.

---
Full diff: https://github.com/llvm/llvm-project/pull/154128.diff


1 Files Affected:

- (modified) llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp (+5-1) 


``````````diff
diff --git a/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp b/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp
index ed73dc8903908..7090bc8124f9c 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp
@@ -2366,8 +2366,12 @@ static bool containsBufferFatPointers(const Function &F,
                                       BufferFatPtrToStructTypeMap *TypeMap) {
   bool HasFatPointers = false;
   for (const BasicBlock &BB : F)
-    for (const Instruction &I : BB)
+    for (const Instruction &I : BB) {
       HasFatPointers |= (I.getType() != TypeMap->remapType(I.getType()));
+      // Catch null pointer constasts in loads, stores, etc.
+      for (const Value *V : I.operand_values())
+        HasFatPointers |= (V->getType() != TypeMap->remapType(V->getType()));
+    }
   return HasFatPointers;
 }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/154128