[AArch64][PAC] Do not execute AUT instructions speculatively

A generic authentication instruction may crash the process on failure.
Furthermore, it can be executed conditionally and/or its signing schema
can be chosen dynamically. For this reason, while it may be beneficial
to permit DCE to remove AUTx16x17 or AUTxMxN instructions unless their
results have any uses (at least fake ones, if we just want to check the
signature), AUT instructions are not safe to be executed speculatively.

As a quick fix for miscompilation possibility, this patch marks AUTxMxN
pseudo instruction as having unmodelled side effects.

Author: atrosinenko

llvm/lib/Target/AArch64/AArch64InstrInfo.td

@@ -2155,7 +2155,7 @@ let Predicates = [HasPAuth] in {
                             i64imm:$Disc, GPR64:$AddrDisc),
                        [], "$AuthVal = $Val">, Sched<[WriteI, ReadI]> {
     let isCodeGenOnly = 1;
-    let hasSideEffects = 0;
+    let hasSideEffects = 1;
     let mayStore = 0;
     let mayLoad = 0;
     let Size = 32;

llvm/test/CodeGen/AArch64/ptrauth-intrinsic-auth-resign.ll

@@ -770,12 +770,14 @@ define ptr @auth_speculation(i64 %signed, i1 %cond) {
 ; UNCHECKED-DARWIN-NEXT:        autdzb  x16
 ; UNCHECKED-DARWIN-NEXT:      [[BB_RETURN]]:
 ; UNCHECKED-DARWIN-NEXT:        ldr     x8, [x16]
-; UNCHECKED-ELF-NEXT:           mov     x8, x0
+; UNCHECKED-ELF-NEXT:           tbz     w1, #0, [[BB_ELSE:[A-Za-z0-9_.]+]]
+; UNCHECKED-ELF-NEXT:         %bb.1:
 ; UNCHECKED-ELF-NEXT:           autdza  x0
-; UNCHECKED-ELF-NEXT:           autdzb  x8
-; UNCHECKED-ELF-NEXT:           tst     w1, #0x1
-; UNCHECKED-ELF-NEXT:           csel    x8, x8, x0, eq
-; UNCHECKED-ELF-NEXT:           ldr     x8, [x8]
+; UNCHECKED-ELF-NEXT:           b       [[BB_RETURN:[A-Za-z0-9_.]+]]
+; UNCHECKED-ELF-NEXT:         [[BB_ELSE]]:
+; UNCHECKED-ELF-NEXT:           autdzb  x0
+; UNCHECKED-ELF-NEXT:         [[BB_RETURN]]:
+; UNCHECKED-ELF-NEXT:           ldr     x8, [x0]
 ; UNCHECKED-NEXT:               ldr     x8, [x8]
 ; UNCHECKED-NEXT:               ldr     x8, [x8]
 ; UNCHECKED-NEXT:               ldr     x0, [x8]
@@ -792,12 +794,14 @@ define ptr @auth_speculation(i64 %signed, i1 %cond) {
 ; CHECKED-DARWIN-NEXT:        autdzb  x16
 ; CHECKED-DARWIN-NEXT:      [[BB_RETURN]]:
 ; CHECKED-DARWIN-NEXT:        ldr     x8, [x16]
-; CHECKED-ELF-NEXT:           mov     x8, x0
+; CHECKED-ELF-NEXT:           tbz     w1, #0, [[BB_ELSE:[A-Za-z0-9_.]+]]
+; CHECKED-ELF-NEXT:         %bb.1:
 ; CHECKED-ELF-NEXT:           autdza  x0
-; CHECKED-ELF-NEXT:           autdzb  x8
-; CHECKED-ELF-NEXT:           tst     w1, #0x1
-; CHECKED-ELF-NEXT:           csel    x8, x8, x0, eq
-; CHECKED-ELF-NEXT:           ldr     x8, [x8]
+; CHECKED-ELF-NEXT:           b       [[BB_RETURN:[A-Za-z0-9_.]+]]
+; CHECKED-ELF-NEXT:         [[BB_ELSE]]:
+; CHECKED-ELF-NEXT:           autdzb  x0
+; CHECKED-ELF-NEXT:         [[BB_RETURN]]:
+; CHECKED-ELF-NEXT:           ldr     x8, [x0]
 ; CHECKED-NEXT:               ldr     x8, [x8]
 ; CHECKED-NEXT:               ldr     x8, [x8]
 ; CHECKED-NEXT:               ldr     x0, [x8]
@@ -826,24 +830,26 @@ define ptr @auth_speculation(i64 %signed, i1 %cond) {
 ; TRAP-DARWIN-NEXT:      [[L]]auth_success_19:
 ; TRAP-DARWIN-NEXT:      [[BB_RETURN]]:
 ; TRAP-DARWIN-NEXT:        ldr     x8, [x16]
-; TRAP-ELF-NEXT:           mov     x8, x0
+; TRAP-ELF-NEXT:           tbz     w1, #0, [[BB_ELSE:[A-Za-z0-9_.]+]]
+; TRAP-ELF-NEXT:         %bb.1:
 ; TRAP-ELF-NEXT:           autdza  x0
-; TRAP-ELF-NEXT:           mov     x9, x0
-; TRAP-ELF-NEXT:           xpacd   x9
-; TRAP-ELF-NEXT:           cmp     x0, x9
+; TRAP-ELF-NEXT:           mov     x8, x0
+; TRAP-ELF-NEXT:           xpacd   x8
+; TRAP-ELF-NEXT:           cmp     x0, x8
 ; TRAP-ELF-NEXT:           b.eq    [[L]]auth_success_18
 ; TRAP-ELF-NEXT:           brk     #0xc472
 ; TRAP-ELF-NEXT:         [[L]]auth_success_18:
-; TRAP-ELF-NEXT:           autdzb  x8
-; TRAP-ELF-NEXT:           mov     x9, x8
-; TRAP-ELF-NEXT:           xpacd   x9
-; TRAP-ELF-NEXT:           cmp     x8, x9
+; TRAP-ELF-NEXT:           b       [[BB_RETURN:[A-Za-z0-9_.]+]]
+; TRAP-ELF-NEXT:         [[BB_ELSE]]:
+; TRAP-ELF-NEXT:           autdzb  x0
+; TRAP-ELF-NEXT:           mov     x8, x0
+; TRAP-ELF-NEXT:           xpacd   x8
+; TRAP-ELF-NEXT:           cmp     x0, x8
 ; TRAP-ELF-NEXT:           b.eq    [[L]]auth_success_19
 ; TRAP-ELF-NEXT:           brk     #0xc473
 ; TRAP-ELF-NEXT:         [[L]]auth_success_19:
-; TRAP-ELF-NEXT:           tst     w1, #0x1
-; TRAP-ELF-NEXT:           csel    x8, x8, x0, eq
-; TRAP-ELF-NEXT:           ldr     x8, [x8]
+; TRAP-ELF-NEXT:         [[BB_RETURN]]:
+; TRAP-ELF-NEXT:           ldr     x8, [x0]
 ; TRAP-NEXT:               ldr     x8, [x8]
 ; TRAP-NEXT:               ldr     x8, [x8]
 ; TRAP-NEXT:               ldr     x0, [x8]