[AArch64][GlobalISel] Look into array's element (#74109)

In AArch64RegisterBankInfo, IsFPOrFPType() does not work correctly
with ArrayTypes and StructTypes as it does not not look at their
elements.

This caused some registers to be selected as gpr instead of fpr.

Author: ChuongGoh-arm

llvm/lib/Target/AArch64/GISel/AArch64RegisterBankInfo.cpp

@@ -621,6 +621,13 @@ bool AArch64RegisterBankInfo::isLoadFromFPType(const MachineInstr &MI) const {
   Type *EltTy = nullptr;
   if (const GlobalValue *GV = dyn_cast<GlobalValue>(LdVal)) {
     EltTy = GV->getValueType();
+    // Look at the first element of the struct to determine the type we are
+    // loading
+    while (StructType *StructEltTy = dyn_cast<StructType>(EltTy))
+      EltTy = StructEltTy->getTypeAtIndex(0U);
+    // Look at the first element of the array to determine its type
+    if (isa<ArrayType>(EltTy))
+      EltTy = EltTy->getArrayElementType();
   } else {
     // FIXME: grubbing around uses is pretty ugly, but with no more
     // `getPointerElementType` there's not much else we can do.

llvm/test/CodeGen/AArch64/GlobalISel/regbankselect-fp-loads.mir

@@ -123,12 +123,12 @@ body:             |
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT:   [[COPY:%[0-9]+]]:gpr(s32) = COPY $w0
   ; CHECK-NEXT:   [[GV:%[0-9]+]]:gpr(p0) = G_GLOBAL_VALUE @array_double
-  ; CHECK-NEXT:   %fp_load:gpr(s64) = G_LOAD [[GV]](p0) :: (dereferenceable load (s64) from @array_double)
+  ; CHECK-NEXT:   %fp_load:fpr(s64) = G_LOAD [[GV]](p0) :: (dereferenceable load (s64) from @array_double)
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT: bb.1:
   ; CHECK-NEXT:   successors: %bb.1(0x40000000), %bb.2(0x40000000)
   ; CHECK-NEXT: {{  $}}
-  ; CHECK-NEXT:   [[PHI:%[0-9]+]]:gpr(s32) = PHI %fp_load(s64), %bb.0, [[PHI]](s32), %bb.1
+  ; CHECK-NEXT:   [[PHI:%[0-9]+]]:fpr(s32) = PHI %fp_load(s64), %bb.0, [[PHI]](s32), %bb.1
   ; CHECK-NEXT:   G_BRCOND [[COPY]](s32), %bb.1
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT: bb.2:
@@ -164,12 +164,12 @@ body:             |
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT:   [[COPY:%[0-9]+]]:gpr(s32) = COPY $w0
   ; CHECK-NEXT:   [[GV:%[0-9]+]]:gpr(p0) = G_GLOBAL_VALUE @struct_array_double
-  ; CHECK-NEXT:   %fp_load:gpr(s64) = G_LOAD [[GV]](p0) :: (dereferenceable load (s64) from @struct_array_double)
+  ; CHECK-NEXT:   %fp_load:fpr(s64) = G_LOAD [[GV]](p0) :: (dereferenceable load (s64) from @struct_array_double)
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT: bb.1:
   ; CHECK-NEXT:   successors: %bb.1(0x40000000), %bb.2(0x40000000)
   ; CHECK-NEXT: {{  $}}
-  ; CHECK-NEXT:   [[PHI:%[0-9]+]]:gpr(s32) = PHI %fp_load(s64), %bb.0, [[PHI]](s32), %bb.1
+  ; CHECK-NEXT:   [[PHI:%[0-9]+]]:fpr(s32) = PHI %fp_load(s64), %bb.0, [[PHI]](s32), %bb.1
   ; CHECK-NEXT:   G_BRCOND [[COPY]](s32), %bb.1
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT: bb.2:
@@ -205,12 +205,12 @@ body:             |
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT:   [[COPY:%[0-9]+]]:gpr(s32) = COPY $w0
   ; CHECK-NEXT:   [[GV:%[0-9]+]]:gpr(p0) = G_GLOBAL_VALUE @struct_struct_array_double
-  ; CHECK-NEXT:   %fp_load:gpr(s64) = G_LOAD [[GV]](p0) :: (dereferenceable load (s64) from @struct_struct_array_double)
+  ; CHECK-NEXT:   %fp_load:fpr(s64) = G_LOAD [[GV]](p0) :: (dereferenceable load (s64) from @struct_struct_array_double)
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT: bb.1:
   ; CHECK-NEXT:   successors: %bb.1(0x40000000), %bb.2(0x40000000)
   ; CHECK-NEXT: {{  $}}
-  ; CHECK-NEXT:   [[PHI:%[0-9]+]]:gpr(s32) = PHI %fp_load(s64), %bb.0, [[PHI]](s32), %bb.1
+  ; CHECK-NEXT:   [[PHI:%[0-9]+]]:fpr(s32) = PHI %fp_load(s64), %bb.0, [[PHI]](s32), %bb.1
   ; CHECK-NEXT:   G_BRCOND [[COPY]](s32), %bb.1
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT: bb.2: