AArch64: Addressing Cortex-A53 erratum 835769.

Some early revisions of the Cortex-A53 have an erratum (835769) whereby
it is possible for a 64-bit multiply-accumulate instruction in AArch64
state to generate an incorrect result. The conditions which a portion
of code must satisfy in order for the issue to be observed are somewhat
complex, but all cases end with a memory (load, store, or prefetch)
instruction followed immediately by the multiply-accumulate operation.

This commit makes sure to insert a nop instruction before a 64-bit msub
instruction, whenever the latter is preceded by a memory instruction.
This behaviour should make it impossible for the Arm64 backend to
generate a sequence of instructions which matches the erratum
conditions.

Change-Id: I0022eccd41180183c20231dab6e2671d001a204c

1 files changed, 16 insertions, 15 deletions

diff --git a/compiler/dex/compiler_enums.h b/compiler/dex/compiler_enums.h
index 5d877fdf80..b56fd6f5c7 100644
--- a/compiler/dex/compiler_enums.h
+++ b/compiler/dex/compiler_enums.h
@@ -610,21 +610,22 @@ std::ostream& operator<<(std::ostream& os, const SelectInstructionKind& kind);
 // LIR fixup kinds for Arm
 enum FixupKind {
   kFixupNone,
-  kFixupLabel,       // For labels we just adjust the offset.
-  kFixupLoad,        // Mostly for immediates.
-  kFixupVLoad,       // FP load which *may* be pc-relative.
-  kFixupCBxZ,        // Cbz, Cbnz.
-  kFixupTBxZ,        // Tbz, Tbnz.
-  kFixupPushPop,     // Not really pc relative, but changes size based on args.
-  kFixupCondBranch,  // Conditional branch
-  kFixupT1Branch,    // Thumb1 Unconditional branch
-  kFixupT2Branch,    // Thumb2 Unconditional branch
-  kFixupBlx1,        // Blx1 (start of Blx1/Blx2 pair).
-  kFixupBl1,         // Bl1 (start of Bl1/Bl2 pair).
-  kFixupAdr,         // Adr.
-  kFixupMovImmLST,   // kThumb2MovImm16LST.
-  kFixupMovImmHST,   // kThumb2MovImm16HST.
-  kFixupAlign4,      // Align to 4-byte boundary.
+  kFixupLabel,             // For labels we just adjust the offset.
+  kFixupLoad,              // Mostly for immediates.
+  kFixupVLoad,             // FP load which *may* be pc-relative.
+  kFixupCBxZ,              // Cbz, Cbnz.
+  kFixupTBxZ,              // Tbz, Tbnz.
+  kFixupPushPop,           // Not really pc relative, but changes size based on args.
+  kFixupCondBranch,        // Conditional branch
+  kFixupT1Branch,          // Thumb1 Unconditional branch
+  kFixupT2Branch,          // Thumb2 Unconditional branch
+  kFixupBlx1,              // Blx1 (start of Blx1/Blx2 pair).
+  kFixupBl1,               // Bl1 (start of Bl1/Bl2 pair).
+  kFixupAdr,               // Adr.
+  kFixupMovImmLST,         // kThumb2MovImm16LST.
+  kFixupMovImmHST,         // kThumb2MovImm16HST.
+  kFixupAlign4,            // Align to 4-byte boundary.
+  kFixupA53Erratum835769,  // Cortex A53 Erratum 835769.
 };
 std::ostream& operator<<(std::ostream& os, const FixupKind& kind);