Testing bit next to signbit does not constant fold when squaring signed integers

[ZERICO2005]

https://godbolt.org/z/7bqs6W8an

bool func_B(int8_t x) {
    return (x * x) & (1 << 30);
}

Assuming that int is 32 bits, then squaring int8_t should clear bits [15, 31] as the result will be [0, 16384]. I noticed that the code is not constant folded to return false when testing bit 30 (the bit next to the signbit). It also generates different llvm compared to testing bits 16-29* (icmp samesign ugt versus icmp ne 0).

Transforming return (x * x) & (1 << 30) to return false appears to be correct:
https://alive2.llvm.org/ce/z/Q6w5gy

*testing bit 15 does not constant fold for different reasons.

[llvmbot]

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[llvmbot]

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Author: None (ZERICO2005)

https://godbolt.org/z/7bqs6W8an ``` bool func_B(int8_t x) { return (x * x) & (1 << 30); } ``` Assuming that `int` is 32 bits, then squaring `int8_t` should clear bits [15, 31] as the result will be [0, 16384]. I noticed that the code is not constant folded to return false when testing bit 30 (the bit next to the signbit). It also generates different llvm compared to testing bits 16-29* (`icmp samesign ugt` versus `icmp ne 0`).

Transforming return (x * x) & (1 << 30) to return false appears to be correct:
https://alive2.llvm.org/ce/z/Q6w5gy

*testing bit 15 does not constant fold for different reasons.