[PATCH] D83153: [DAGCombiner] Prevent regression in isMulAddWithConstProfitable

[Ben Shi via Phabricator via llvm-commits]

benshi001 marked an inline comment as done.
benshi001 added inline comments.


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Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:15755-15759
+        // This transform will introduce regression, if c1 is legal add
+        // immediate while c1*c2 isn't.
+        const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+        if (TLI.isLegalAddImmediate(C1) && !TLI.isLegalAddImmediate(C1C2))
+          return false;
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benshi001 wrote:
> spatel wrote:
> > lebedev.ri wrote:
> > > You also need a second piece if the puzzle, because we would have
> > > already performed this transform before ever getting here:
> > > https://godbolt.org/z/TE_bzk
> > > 
> > > You need to add an inverse transform into DAGCombiner.cpp.
> > Right - I asked if the motivation for this was GEP math:
> > http://lists.llvm.org/pipermail/llvm-dev/2020-July/142979.html
> > ...but I did not see an answer.
> > 
> > If yes, then we should have GEP tests. If not, then this patch isn't enough.
> No. I target for normal IR transform, not GEP.
> 
> So I need to do a inverse transform?
Where is the other place perform the same transform before reach here?


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https://reviews.llvm.org/D83153