Date: Sun, 28 Jul 2024 11:14:06 GMT From: Dimitry Andric <dim@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 1a4b8325f6e3 - main - Merge commit c80c09f3e380 from llvm-project (by Dimitry Andric): Message-ID: <202407281114.46SBE6DZ018717@gitrepo.freebsd.org>
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The branch main has been updated by dim: URL: https://cgit.FreeBSD.org/src/commit/?id=1a4b8325f6e3a45c77188343da504fe04495cc46 commit 1a4b8325f6e3a45c77188343da504fe04495cc46 Author: Dimitry Andric <dim@FreeBSD.org> AuthorDate: 2024-07-28 11:13:37 +0000 Commit: Dimitry Andric <dim@FreeBSD.org> CommitDate: 2024-07-28 11:13:37 +0000 Merge commit c80c09f3e380 from llvm-project (by Dimitry Andric): [CalcSpillWeights] Avoid x87 excess precision influencing weight result Fixes #99396 The result of `VirtRegAuxInfo::weightCalcHelper` can be influenced by x87 excess precision, which can result in slightly different register choices when the compiler is hosted on x86_64 or i386. This leads to different object file output when cross-compiling to i386, or native. Similar to 7af3432e22b0, we need to add a `volatile` qualifier to the local `Weight` variable to force it onto the stack, and avoid the excess precision. Define `stack_float_t` in `MathExtras.h` for this purpose, and use it. This is the version of the fix for PR276961 that landed upstream. PR: 276961 Reported by: cperciva MFC after: 3 days --- contrib/llvm-project/llvm/include/llvm/Support/MathExtras.h | 8 ++++++++ contrib/llvm-project/llvm/lib/CodeGen/CalcSpillWeights.cpp | 11 ++++++----- 2 files changed, 14 insertions(+), 5 deletions(-) diff --git a/contrib/llvm-project/llvm/include/llvm/Support/MathExtras.h b/contrib/llvm-project/llvm/include/llvm/Support/MathExtras.h index aa4f4d2ed42e..afb4fa262152 100644 --- a/contrib/llvm-project/llvm/include/llvm/Support/MathExtras.h +++ b/contrib/llvm-project/llvm/include/llvm/Support/MathExtras.h @@ -644,6 +644,14 @@ std::enable_if_t<std::is_signed_v<T>, T> MulOverflow(T X, T Y, T &Result) { return UX > (static_cast<U>(std::numeric_limits<T>::max())) / UY; } +/// Type to force float point values onto the stack, so that x86 doesn't add +/// hidden precision, avoiding rounding differences on various platforms. +#if defined(__i386__) || defined(_M_IX86) +using stack_float_t = volatile float; +#else +using stack_float_t = float; +#endif + } // End llvm namespace #endif diff --git a/contrib/llvm-project/llvm/lib/CodeGen/CalcSpillWeights.cpp b/contrib/llvm-project/llvm/lib/CodeGen/CalcSpillWeights.cpp index f3cb7fa5af61..fa7ef669ec11 100644 --- a/contrib/llvm-project/llvm/lib/CodeGen/CalcSpillWeights.cpp +++ b/contrib/llvm-project/llvm/lib/CodeGen/CalcSpillWeights.cpp @@ -22,6 +22,7 @@ #include "llvm/CodeGen/TargetSubtargetInfo.h" #include "llvm/CodeGen/VirtRegMap.h" #include "llvm/Support/Debug.h" +#include "llvm/Support/MathExtras.h" #include "llvm/Support/raw_ostream.h" #include <cassert> #include <tuple> @@ -256,7 +257,9 @@ float VirtRegAuxInfo::weightCalcHelper(LiveInterval &LI, SlotIndex *Start, return -1.0f; } - float Weight = 1.0f; + // Force Weight onto the stack so that x86 doesn't add hidden precision, + // similar to HWeight below. + stack_float_t Weight = 1.0f; if (IsSpillable) { // Get loop info for mi. if (MI->getParent() != MBB) { @@ -283,11 +286,9 @@ float VirtRegAuxInfo::weightCalcHelper(LiveInterval &LI, SlotIndex *Start, Register HintReg = copyHint(MI, LI.reg(), TRI, MRI); if (!HintReg) continue; - // Force hweight onto the stack so that x86 doesn't add hidden precision, + // Force HWeight onto the stack so that x86 doesn't add hidden precision, // making the comparison incorrectly pass (i.e., 1 > 1 == true??). - // - // FIXME: we probably shouldn't use floats at all. - volatile float HWeight = Hint[HintReg] += Weight; + stack_float_t HWeight = Hint[HintReg] += Weight; if (HintReg.isVirtual() || MRI.isAllocatable(HintReg)) CopyHints.insert(CopyHint(HintReg, HWeight)); }
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