[PATCH] D37928: [ConstantFold] Return the correct type when folding a GEP with vector indices

[Davide Italiano via Phabricator via llvm-commits]

davide created this revision.

As Eli pointed out (and I got wrong in the first place), langref says: "The getelementptr returns a vector of pointers, instead of a single address, when one or more of its arguments is a vector. In such cases, all vector arguments should have the same number of elements, and every scalar argument will be effectively broadcast into a vector during address calculation."

Costantfold for gep doesn't really take in account this paragraph, returning a pointer instead of a vector of pointer which triggers an assertion in RAUW, as we're trying to replace values with mistmatching types.


https://reviews.llvm.org/D37928

Files:
  lib/IR/ConstantFold.cpp
  test/Transforms/InstCombine/pr34627.ll


Index: test/Transforms/InstCombine/pr34627.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstCombine/pr34627.ll
@@ -0,0 +1,11 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -instcombine %s |FileCheck %s
+
+define <2 x i16> @patatino() {
+; CHECK-LABEL: @patatino(
+; CHECK-NEXT:    ret <2 x i16> zeroinitializer
+;
+  %tmp2 = getelementptr inbounds [1 x i16], [1 x i16]* null, i16 0, <2 x i16> undef
+  %tmp3 = ptrtoint <2 x i16*> %tmp2 to <2 x i16>
+  ret <2 x i16> %tmp3
+}
Index: lib/IR/ConstantFold.cpp
===================================================================
--- lib/IR/ConstantFold.cpp
+++ lib/IR/ConstantFold.cpp
@@ -2065,6 +2065,18 @@
       Type *GEPTy = PointerType::get(Ty, PtrTy->getAddressSpace());
       if (VectorType *VT = dyn_cast<VectorType>(C->getType()))
         GEPTy = VectorType::get(GEPTy, VT->getNumElements());
+
+      // The GEP returns a vector of pointers when one of more of
+      // its arguments is a vector.
+      for (unsigned i = 0, e = Idxs.size(); i != e; ++i) {
+        if (auto *VT = dyn_cast<VectorType>(Idxs[i]->getType())) {
+          GEPTy =
+              VectorType::get(PointerType::get(Ty, PtrTy->getAddressSpace()),
+                              VT->getNumElements());
+          break;
+        }
+      }
+
       return Constant::getNullValue(GEPTy);
     }
   }


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