[clang] [llvm] [AArch64][SVE] Lower unpredicated loads/stores as LDR/STR. (PR #127837)

[Paul Walker via cfe-commits]

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@@ -2993,6 +2993,22 @@ let Predicates = [HasSVE_or_SME] in {
   defm : unpred_loadstore_bitcast<nxv2i64>;
   defm : unpred_loadstore_bitcast<nxv2f64>;
 
+  // Allow using LDR/STR to avoid the predicate dependence.
+  let Predicates = [IsLE, AllowMisalignedMemAccesses] in
+    foreach Ty = [ nxv16i8, nxv8i16, nxv4i32, nxv2i64, nxv8f16, nxv4f32, nxv2f64, nxv8bf16 ] in {
+      let AddedComplexity = 2 in {
+        def : Pat<(Ty (load (am_sve_indexed_s9 GPR64sp:$base, simm9:$offset))),
+                  (LDR_ZXI GPR64sp:$base, simm9:$offset)>;
+        def : Pat<(store Ty:$val, (am_sve_indexed_s9 GPR64sp:$base, simm9:$offset)),
+                  (STR_ZXI ZPR:$val, GPR64sp:$base, simm9:$offset)>;
+      }
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paulwalker-arm wrote:

I just wrote something similar and agree it certainly looks wrong.  Nesting classes and setting `Predicate` never really works the way you'd expect.  You often need to know the parent value and duplicate it.

My guess here is that because the Predicate is set with a multi-class it is being overridden by the Predicate value at the point the multi-class is instantiated.  Your PR avoids this but then is most likely overriding in the other direction and stripping `HasSVE`.  The only reason that does not cause any issues is because we will not get this far without the `+sve` support anyway.

https://github.com/llvm/llvm-project/pull/127837