Add TargetOptions::min_global_align, with s390x at 16-bit
#44440
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The SystemZ `LALR` instruction provides PC-relative addressing for globals, but only to *even* addresses, so other compilers make sure that such globals are always 2-byte aligned. In Clang, this is modeled with `TargetInfo::MinGlobalAlign`, and `TargetOptions::min_global_align` now serves the same purpose for rustc. In Clang, the only targets that set this are SystemZ, Lanai, and NVPTX, and the latter two don't have targets in rust master.
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r? @alexcrichton or @japaric |
| // which can force it to be smaller. Rust doesn't support this yet. | ||
| if let Some(min) = ccx.sess().target.target.options.min_global_align { | ||
| match ty::layout::Align::from_bits(min, min) { | ||
| Ok(min) => align = cmp::max(align, min.abi() as machine::llalign), |
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There's a .min method on Align, you should use that.
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We want the greater of the two, so it would be Align::max. But this would require converting the incoming machine::llalign to Align, comparing, then back to llalign for the LLVM call. I don't see the point of that.
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Well, llalign should have never existed etc. etc. I'll just have to remember fixing it on my branch where it's gone, but the rebase should catch it because of type mismatches and whatnot.
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Maybe it's also pointless to convert min_global_align to Align. I just figured a little sanity checking of that value would be good.
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That conversion is fine, since it will be in there sooner or later! In the future I plan to have librustc_back and a lot of librustc/ty/layout.rs be in the same crate so even the target specification would use it.
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📌 Commit c606e97 has been approved by |
Add `TargetOptions::min_global_align`, with s390x at 16-bit The SystemZ `LALR` instruction provides PC-relative addressing for globals, but only to *even* addresses, so other compilers make sure that such globals are always 2-byte aligned. In Clang, this is modeled with `TargetInfo::MinGlobalAlign`, and `TargetOptions::min_global_align` now serves the same purpose for rustc. In Clang, the only targets that set this are SystemZ, Lanai, and NVPTX, and the latter two don't have targets in rust master. Fixes #44411. r? @eddyb
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☀️ Test successful - status-appveyor, status-travis |
The SystemZ
LALRinstruction provides PC-relative addressing for globals,but only to even addresses, so other compilers make sure that such
globals are always 2-byte aligned. In Clang, this is modeled with
TargetInfo::MinGlobalAlign, andTargetOptions::min_global_alignnowserves the same purpose for rustc.
In Clang, the only targets that set this are SystemZ, Lanai, and NVPTX, and
the latter two don't have targets in rust master.
Fixes #44411.
r? @eddyb