[llvm] [GlobalIsel] combine extract vector element (PR #91922)

[Matt Arsenault via llvm-commits]

Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>
Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/91922 at github.com>


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@@ -453,3 +453,162 @@ bool CombinerHelper::matchInsertVectorElementOOB(MachineInstr &MI,
 
   return false;
 }
+
+bool CombinerHelper::isConstantAtOffset(Register Src, const APInt &Index,
+                                        unsigned Depth) {
+  assert(MRI.getType(Src).isVector() && "expected a vector as input");
+  if (Depth == 2)
+    return false;
+
+  // We use the look through variant for higher hit rate and to increase the
+  // likelyhood of constant folding. The actual value is ignored. We only test
+  // *whether* there is a constant.
+
+  MachineInstr *SrcMI = getDefIgnoringCopies(Src, MRI);
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arsenm wrote:

But this should be taken care of by copy->copy folding? I think we should mostly be removing all the getDefIgnoringCopies calls 

https://github.com/llvm/llvm-project/pull/91922