[llvm] [InstCombine] Canonicalize scalable GEPs to use llvm.vscale intrinsic (PR #90569)

[David Green via llvm-commits]

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@@ -2787,6 +2787,14 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
                                     GEP.isInBounds()));
   }
 
+  // Canonicalize scalable GEPs to an explicit offset using the llvm.vscale
+  // intrinsic. This has better support in BasicAA.
+  if (IsGEPSrcEleScalable) {
+    Value *Offset = EmitGEPOffset(cast<GEPOperator>(&GEP));
+    return replaceInstUsesWith(
+        GEP, Builder.CreatePtrAdd(PtrOp, Offset, "", GEP.isInBounds()));
+  }
+
   // Check to see if the inputs to the PHI node are getelementptr instructions.
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davemgreen wrote:

There is a check for IsGEPSrcEleScalable below (and a comment), that could be removed now?

https://github.com/llvm/llvm-project/pull/90569