[compiler-rt] [flang] [lldb] [lld] [clang] [llvm] [libcxxabi] [libcxx] [clang-tools-extra] [AMDGPU] GFX12: select @llvm.prefetch intrinsic (PR #74576)

[Jay Foad via cfe-commits]

================
@@ -959,6 +967,32 @@ def : GCNPat <
 }
 } // let OtherPredicates = [HasShaderCyclesRegister]
 
+def SIMM24bitPtr : ImmLeaf <iPTR,
+  [{return isInt<24>(Imm);}]
+>;
+
+multiclass SMPrefetchPat<string type, int cache_type> {
+  def : GCNPat <
+    (smrd_prefetch (SMRDImm i64:$sbase, i32:$offset), timm, timm, (i32 cache_type)),
+    (!cast<SM_Prefetch_Pseudo>("S_PREFETCH_"#type) $sbase, $offset, (i32 SGPR_NULL), (i8 0))
+  >;
+
+  def : GCNPat <
+    (smrd_prefetch (i64 SReg_64:$sbase), timm, timm, (i32 cache_type)),
+    (!cast<SM_Prefetch_Pseudo>("S_PREFETCH_"#type) $sbase, 0, (i32 SGPR_NULL), (i8 0))
+  >;
+
+  def : GCNPat <
+    (prefetch SIMM24bitPtr:$offset, timm, timm, (i32 cache_type)),
+    (!cast<SM_Prefetch_Pseudo>("S_PREFETCH_"#type#"_PC_REL") (as_i32timm $offset), (i32 SGPR_NULL), (i8 0))
+  > {
+    let AddedComplexity = 10;
+  }
----------------
jayfoad wrote:

I really don't know. What would the use cases look like? Maybe it could be a generic intrinsic, if there is consensus that it is useful.

For the existing llvm.prefetch intrinsic, the only useful case I think of for instruction prefetching is:
```
define @f0() {
  call @llvm.prefetch(@f1, ...) 
  ...
  call @f1()
}
define @f1() { ... }
```
to prefetch the code at the start of a function you are going to call. We could codegen that case using the _pc_rel form of the instruction.

https://github.com/llvm/llvm-project/pull/74576