[llvm] [AArch64] Stop reserved registers from being saved in prolog/epilog (PR #138448)

[Nuko Y. via llvm-commits]

================
@@ -1,43 +1,303 @@
-; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc < %s -mtriple=aarch64-unknown-linux-gnu -reserve-regs-for-regalloc=LR,FP,X28,X27,X26,X25,X24,X23,X22,X21,X20,X19,X18,X17,X16,X15,X14,X13,X12,X11,X10,X9,X8,X7,X6,X5,X4 | FileCheck %s
-; RUN: llc < %s -mtriple=aarch64-unknown-linux-gnu -reserve-regs-for-regalloc=X30,X29,X28,X27,X26,X25,X24,X23,X22,X21,X20,X19,X18,X17,X16,X15,X14,X13,X12,X11,X10,X9,X8,X7,X6,X5,X4 | FileCheck %s
-
-; LR, FP, X30 and X29 should be correctly recognized and not used.
-
-define void @foo(i64 %v1, i64 %v2, ptr %ptr) {
-; CHECK-LABEL: foo:
-; CHECK:       // %bb.0:
-; CHECK-NEXT:    sub sp, sp, #16
-; CHECK-NEXT:    .cfi_def_cfa_offset 16
-; CHECK-NEXT:    add x3, x0, x1
-; CHECK-NEXT:    str x3, [sp, #8] // 8-byte Folded Spill
-; CHECK-NEXT:    str x3, [x2, #8]
-; CHECK-NEXT:    ldr x3, [x2, #16]
-; CHECK-NEXT:    add x3, x0, x3
-; CHECK-NEXT:    sub x3, x3, x1
-; CHECK-NEXT:    str x3, [x2, #16]
-; CHECK-NEXT:    ldr x3, [sp, #8] // 8-byte Folded Reload
-; CHECK-NEXT:    str x3, [x2, #24]
-; CHECK-NEXT:    str x0, [x2, #32]
-; CHECK-NEXT:    str x1, [x2, #40]
-; CHECK-NEXT:    add sp, sp, #16
-; CHECK-NEXT:    ret
-  %v3 = add i64 %v1, %v2
-  %p1 = getelementptr i64, ptr %ptr, i64 1
-  store volatile i64 %v3, ptr %p1, align 8
-
-  %p2 = getelementptr i64, ptr %ptr, i64 2
-  %v4 = load volatile i64, ptr %p2, align 8
-  %v5 = add i64 %v1, %v4
-  %v6 = sub i64 %v5, %v2
-  store volatile i64 %v6, ptr %p2, align 8
-
-  %p3 = getelementptr i64, ptr %ptr, i64 3
-  store volatile i64 %v3, ptr %p3, align 8
-
-  %p4 = getelementptr i64, ptr %ptr, i64 4
-  store volatile i64 %v1, ptr %p4, align 8
-  %p5 = getelementptr i64, ptr %ptr, i64 5
-  store volatile i64 %v2, ptr %p5, align 8
+;; Check if manually reserved registers are always excluded from being saved by
+;; the function prolog/epilog, even for callee-saved ones, as per GCC behavior.
+;; X19(BP, LLVM specific), X29(FP), X30(LP), X31(SP) are special so
+;; they are not checked.
+
+; RUN: llc < %s -mtriple=aarch64-unknown-linux-gnu | FileCheck %s
+
+define void @t1() "target-features"="+reserve-x1" {
----------------
yasuna-oribe wrote:

I didn't know of that I've changed these to be preserve_mostcc but I'll remove X0-X8 and X16-X18 (never preserved) too if you want.

https://github.com/llvm/llvm-project/pull/138448