RFR: 8338197: [ubsan] ad_x86.hpp:6417:11: runtime error: shift exponent 100 is too large for 32-bit type 'unsigned int' [v6]

[Andrew Dinn]

On Mon, 6 Oct 2025 08:34:42 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Boris Ulasevich has refreshed the contents of this pull request, and previous commits have been removed. Incremental views are not available. The pull request now contains three commits:
>> 
>>  - use uint32_t for _mask
>>  - remove redundant code
>>  - 8338197: ubsan: ad_x86.hpp:6417:11: runtime error: shift exponent 100 is too large for 32-bit type 'unsigned int'
>
> src/hotspot/share/adlc/output_h.cpp line 768:
> 
>> 766:     fprintf(fp_hpp, "  }\n\n");
>> 767:     fprintf(fp_hpp, "  Pipeline_Use_Cycle_Mask& operator<<=(int n) {\n");
>> 768:     fprintf(fp_hpp, "    _mask <<= (n < 32) ? n : 31;\n");
> 
> I was staring at this line for a while. Isn't this cutting too early? I would have expected `n=32` case to zero out the mask completely. Instead, this code moves lowest bit to highest bit, as it performs 31-bit shift. Should it be something like `_mask = (n < 32) ? (_mask << n) : 0;`?

This is arguably correct. However, it doesn't really matter much whether we cap the depth at(n) at 32 or 31 because for all current pipeline models the pipeline depth is always way less than 31.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26890#discussion_r2405908503