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Merge fixes for a couple cases where the compiler generated different i386 code depending on the host. In the base system this showed up as very small differences in a couple object files in buildworld for i386 depending on the host architecture (i386 or amd64). PR: 276961
43 lines
1.8 KiB
Text
43 lines
1.8 KiB
Text
commit 397c2693fa66508cb5e6b173650a1f3bc6c4dd4f
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Author: Dimitry Andric <dim@FreeBSD.org>
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Date: Sun Jul 21 22:37:27 2024 +0200
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Fix llvm register allocator for native/cross build differences
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Work around an issue in LLVM's register allocator, which can cause
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slightly different i386 object files, when produced by a native or cross
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build of clang.
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This adds another volatile qualifier to a float variable declaration in
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the weightCalcHelper() function, which otherwise produces slightly
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different float results on amd64 and i386 hosts. In turn, this can lead
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to different (but equivalent) register choices, and thus non-identical
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assembly code.
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See https://github.com/llvm/llvm-project/issues/99396 for more details.
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Note this is a temporary fix, meant to merge in time for 13.4. As soon
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as upstream has a permanent solution we will import that.
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PR: 276961
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Reported by: cperciva
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MFC after: 3 days
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diff --git llvm/lib/CodeGen/CalcSpillWeights.cpp llvm/lib/CodeGen/CalcSpillWeights.cpp
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index f3cb7fa5af61..afde8d001f88 100644
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--- llvm/lib/CodeGen/CalcSpillWeights.cpp
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+++ llvm/lib/CodeGen/CalcSpillWeights.cpp
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@@ -256,7 +256,12 @@ float VirtRegAuxInfo::weightCalcHelper(LiveInterval &LI, SlotIndex *Start,
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return -1.0f;
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}
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- float Weight = 1.0f;
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+ // FreeBSD customization: similar to the HWeight declaration below, add a
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+ // volatile qualifier to avoid slightly different weight results on amd64
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+ // and i386 hosts, and possibly choosing different registers in the register
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+ // allocator. See <https://github.com/llvm/llvm-project/issues/99396> for
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+ // more details.
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+ volatile float Weight = 1.0f;
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if (IsSpillable) {
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// Get loop info for mi.
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if (MI->getParent() != MBB) {
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