[llvm] [BOLT][AArch64] Speedup `computeInstructionSize` (PR #121106)

[Vladislav Khmelevsky via llvm-commits]

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@@ -1363,6 +1363,17 @@ class BinaryContext {
     if (std::optional<uint32_t> Size = MIB->getSize(Inst))
       return *Size;
 
+    // Pseudo instrs will not be emiitted and have no size.
+    if (MIB->isPseudo(Inst)) {
+      return 0;
+    }
+
+    // Directly return 4 because AArch64 instructions always have a
+    // fixed size of 4 bytes.
+    if (isAArch64()) {
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yota9 wrote:

I mean that "getSize" declaration should be final. And first of all we should check annotations in getSize. But if no annotation presented we should call getInstructionSize()/getTargetSize()/etc that would be target-specific directly from getSize() that would return  the same optional uint32_t. Default implementation of getInstructionSize() should return  std::nullopt. 

https://github.com/llvm/llvm-project/pull/121106