[LLVM][AArch64InstrInfo] Prevent fill folding when DstReg is SP.

We can remove subreg COPY instructions by filling directly into the
COPY's destination register. However, this is only valid when the copy
and fill have compatible register classes.

Fixes #148659

Author: paulwalker-arm

llvm/lib/Target/AArch64/AArch64InstrInfo.cpp

@@ -6294,7 +6294,8 @@ MachineInstr *AArch64InstrInfo::foldMemoryOperandImpl(
         FillRC = nullptr;
         break;
       case AArch64::sub_32:
-        FillRC = &AArch64::GPR32RegClass;
+        if (AArch64::GPR64RegClass.hasSubClassEq(getRegClass(DstReg)))
+          FillRC = &AArch64::GPR32RegClass;
         break;
       case AArch64::ssub:
         FillRC = &AArch64::FPR32RegClass;

llvm/test/CodeGen/AArch64/spill-fold.mir

@@ -10,6 +10,7 @@
   define i64 @test_subreg_fill_fold() { ret i64 0 }
   define double @test_subreg_fill_fold2() { ret double 0.0 }
   define <4 x float> @test_subreg_fill_fold3() { ret <4 x float> undef }
+  define i64 @test_subreg_fill_fold4() { ret i64 0 }
   define i64 @test_nzcv_spill_fold() { ret i64 0 }
 ...
 ---
@@ -121,6 +122,24 @@ body:             |
     RET_ReallyLR implicit $s0
 ...
 ---
+# CHECK-LABEL: name: test_subreg_fill_fold4
+# Ensure the COPY is maintained when its result register class is not compatible
+# with the fill load's.
+name:            test_subreg_fill_fold4
+registers:
+  - { id: 0, class: gpr32 }
+  - { id: 1, class: gpr64sp }
+body:             |
+  bb.0:
+    %0 = COPY $wzr
+    INLINEASM &nop, 1, 12, implicit-def dead $x0, 12, implicit-def dead $x1, 12, implicit-def dead $x2, 12, implicit-def dead $x3, 12, implicit-def dead $x4, 12, implicit-def dead $x5, 12, implicit-def dead $x6, 12, implicit-def dead $x7, 12, implicit-def dead $x8, 12, implicit-def dead $x9, 12, implicit-def dead $x10, 12, implicit-def dead $x11, 12, implicit-def dead $x12, 12, implicit-def dead $x13, 12, implicit-def dead $x14, 12, implicit-def dead $x15, 12, implicit-def dead $x16, 12, implicit-def dead $x17, 12, implicit-def dead $x18, 12, implicit-def dead $x19, 12, implicit-def dead $x20, 12, implicit-def dead $x21, 12, implicit-def dead $x22, 12, implicit-def dead $x23, 12, implicit-def dead $x24, 12, implicit-def dead $x25, 12, implicit-def dead $x26, 12, implicit-def dead $x27, 12, implicit-def dead $x28, 12, implicit-def dead $fp, 12, implicit-def dead $lr, 12, implicit-def $sp
+    ; CHECK: %2:gpr32 = LDRWui %stack.0, 0 :: (load (s32) from %stack.0)
+    ; CHECK: undef %1.sub_32:gpr64sp = COPY %2
+    undef %1.sub_32:gpr64sp = COPY %0
+    $x0 = COPY %1
+    RET_ReallyLR implicit $x0
+...
+---
 # CHECK-LABEL: name: test_nzcv_spill_fold
 # Ensure that nzcv COPY cannot be folded.
 name:            test_nzcv_spill_fold