[AMDGPU][LowerBufferFatPointers] Erase dead ptr(7) intrinsics (#160798)

Fix a crash that would arise when intrinsics like llvm.masked.load.T.p7
were left in the module when AMDGPULowerBufferFatPointers was applied
and so a captures(none) annotation would be applied to a non-pointer
value, triggering a verifier failure.

---------

Co-authored-by: Shilei Tian <i@tianshilei.me>

Author: krzysz00

llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp

@@ -2562,7 +2562,9 @@ bool AMDGPULowerBufferFatPointers::run(Module &M, const TargetMachine &TM) {
   for (Function *F : NeedsPostProcess)
     Splitter.processFunction(*F);
   for (Function *F : Intrinsics) {
-    if (isRemovablePointerIntrinsic(F->getIntrinsicID())) {
+    // use_empty() can also occur with cases like masked load, which will
+    // have been rewritten out of the module by now but not erased.
+    if (F->use_empty() || isRemovablePointerIntrinsic(F->getIntrinsicID())) {
       F->eraseFromParent();
     } else {
       std::optional<Function *> NewF = Intrinsic::remangleIntrinsicFunction(F);

llvm/test/CodeGen/AMDGPU/lower-buffer-fat-pointers-dead-intrinsics.ll

@@ -0,0 +1,9 @@
+; RUN: opt -S -mtriple=amdgcn-amd-amdhsa -mcpu=gfx900 -amdgpu-lower-buffer-fat-pointers < %s | FileCheck %s
+; RUN: opt -S -mtriple=amdgcn-amd-amdhsa -mcpu=gfx900 -passes=amdgpu-lower-buffer-fat-pointers < %s | FileCheck %s
+
+; CHECK: @arbitrary
+declare amdgpu_kernel void @arbitrary(ptr addrspace(1))
+
+; COM: This used to cause verifier errors when "lowered"
+declare <4 x i8> @llvm.masked.load.v4i8.p7(ptr addrspace(7) captures(none), i32 immarg, <4 x i1>, <4 x i8>)
+; CHECK-NOT: llvm.masked.load