[PATCH] D81900: Add coverage for inexact constant folding for multiplication in Selection DAG

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


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Comment at: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:5139-5140
+          RHS.multiply(LHS, APFloat::rmNearestTiesToEven);
+      if (((status & APFloat::opInexact) == 0) ||
+          getTarget().Options.UnsafeFPMath) {
+        return getConstantFP(RHS, DL, VT);
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mcberg2017 wrote:
> arsenm wrote:
> > I'm not sure I understand why this would depend on unsafe math. Why does it matter if it was inexact? The unconstrained operations have the defined rounding mode
> With Unsafe any contracts concerning the ability to deliver infinite precision are broken, ergo Unsafe overrides and allows the result regardless as precision is relaxed and its behavior as well.
But why would there be any expectation of infinite precision here? It's the precision of the fltSemantics. I also don't understand why this would be tied to the global UnsafeFPMath option, and not something more refined


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D81900/new/

https://reviews.llvm.org/D81900