[llvm] [X86] Fix 32-bit immediate assertion and convert into backend error (PR #123872)

[Simon Pilgrim via llvm-commits]

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@@ -965,11 +965,10 @@ X86RegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
   }
 
   if (MI.getOperand(FIOperandNum+3).isImm()) {
-    // Offset is a 32-bit integer.
-    int Imm = (int)(MI.getOperand(FIOperandNum + 3).getImm());
-    int Offset = FIOffset + Imm;
-    assert((!Is64Bit || isInt<32>((long long)FIOffset + Imm)) &&
-           "Requesting 64-bit offset in 32-bit immediate!");
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RKSimon wrote:

This assert was checking to see if Offset addition overflowed on x86-64 - haven't we lost that check now?

https://github.com/llvm/llvm-project/pull/123872