git: 814641415fbe - stable/13 - Merge commit c80c09f3e380 from llvm-project (by Dimitry Andric):

The branch stable/13 has been updated by dim:

URL: https://cgit.FreeBSD.org/src/commit/?id=814641415fbee707b312c334e00a1ebb5157e37b

commit 814641415fbee707b312c334e00a1ebb5157e37b
Author:     Dimitry Andric <dim@FreeBSD.org>
AuthorDate: 2024-07-28 11:13:37 +0000
Commit:     Dimitry Andric <dim@FreeBSD.org>
CommitDate: 2024-07-31 07:29:59 +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
    
    (cherry picked from commit 1a4b8325f6e3a45c77188343da504fe04495cc46)
---
 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));
   }