[llvm] [AArch64][GlobalISel] Fix incorrect codegen for FPR16/FPR8 to GPR copies (PR #171499)

[Sam Schweigel via llvm-commits]

xal-0 wrote:

I would guess this could be handled more easily in legalization, or in `AArch64InstructionSelector::select`, which already has some special handling for stronger-than-monotonic stores. `copyPhysReg` feels like the wrong place to me.

This change to legalization fixes the bug and handles a pair of TODOs:
```diff
diff --git i/llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp w/llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
index 44a148940ec9..1761b356b655 100644
--- i/llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
+++ w/llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
@@ -568,6 +568,10 @@ AArch64LegalizerInfo::AArch64LegalizerInfo(const AArch64Subtarget &ST)
         return Query.Types[0] == s128 &&
                Query.MMODescrs[0].Ordering != AtomicOrdering::NotAtomic;
       })
+      .widenScalarIf(
+          all(scalarNarrowerThan(0, 32),
+              atomicOrderingAtLeastOrStrongerThan(0, AtomicOrdering::Release)),
+          changeTo(0, s32))
       .legalForTypesWithMemDesc(
           {{s8, p0, s8, 8},     {s16, p0, s8, 8},  // truncstorei8 from s16
            {s32, p0, s8, 8},                       // truncstorei8 from s32
diff --git i/llvm/test/CodeGen/AArch64/Atomics/aarch64-atomic-store-rcpc_immo.ll w/llvm/test/CodeGen/AArch64/Atomics/aarch64-atomic-store-rcpc_immo.ll
index c80b18d17888..8bf5e41318b8 100644
--- i/llvm/test/CodeGen/AArch64/Atomics/aarch64-atomic-store-rcpc_immo.ll
+++ w/llvm/test/CodeGen/AArch64/Atomics/aarch64-atomic-store-rcpc_immo.ll
@@ -357,12 +357,10 @@ define void @store_atomic_i128_unaligned_seq_cst(i128 %value, ptr %ptr) {
     ret void
 }
 
-; TODO: missed opportunity to emit a stlurb w/ GISel
 define void @store_atomic_i8_from_gep() {
 ; GISEL-LABEL: store_atomic_i8_from_gep:
 ; GISEL:    bl init
-; GISEL:    add x9, x8, #1
-; GISEL:    stlrb w8, [x9]
+; GISEL:    stlurb w8, [x9, #1]
 ;
 ; SDAG-LABEL: store_atomic_i8_from_gep:
 ; SDAG:    bl init
@@ -378,8 +376,7 @@ define void @store_atomic_i8_from_gep() {
 define void @store_atomic_i16_from_gep() {
 ; GISEL-LABEL: store_atomic_i16_from_gep:
 ; GISEL:    bl init
-; GISEL:    add x9, x8, #2
-; GISEL:    stlrh w8, [x9]
+; GISEL:    stlurh w8, [x9, #2]
 ;
 ; SDAG-LABEL: store_atomic_i16_from_gep:
 ; SDAG:    bl init
```

https://github.com/llvm/llvm-project/pull/171499