[llvm] [X86] getIntImmCostInst - recognise i64 ICMP EQ/NE special cases (PR #142812)

[Simon Pilgrim via llvm-commits]

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@@ -5993,12 +5993,19 @@ InstructionCost X86TTIImpl::getIntImmCostInst(unsigned Opcode, unsigned Idx,
     // This is an imperfect hack to prevent constant hoisting of
     // compares that might be trying to check if a 64-bit value fits in
     // 32-bits. The backend can optimize these cases using a right shift by 32.
-    // Ideally we would check the compare predicate here. There also other
-    // similar immediates the backend can use shifts for.
+    // There are other predicates and immediates the backend can use shifts for.
     if (Idx == 1 && ImmBitWidth == 64) {
       uint64_t ImmVal = Imm.getZExtValue();
       if (ImmVal == 0x100000000ULL || ImmVal == 0xffffffff)
         return TTI::TCC_Free;
+
+      if (auto *Cmp = dyn_cast_or_null<CmpInst>(Inst)) {
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RKSimon wrote:

It's not guaranteed that an Instruction is available to pass to the cost call, that's why Opcode is passed separately and we don't get from I->getOpcode().

https://github.com/llvm/llvm-project/pull/142812