[InstSimplify] Deduce correct type for vector gep

[davide]

Summary

Fixes
http://bugs.llvm.org/show_bug.cgi?id=32697

Thanks to Filipe for pointing out the three gep vector variants to cover

[filcab]

LGTM

[spatel]

Since we already have a test file specifically for vector gep simplifications (test/Transforms/InstSimplify/vector_gep.ll), can you please add these new tests there? I find it easier to locate and fix bugs when related tests are co-located. A comment/link back to http://bugs.llvm.org/show_bug.cgi?id=32697 above the regression test also saves time for future bug hunting. Thanks!

[davide]

In D32180#730382, @spatel wrote:

Since we already have a test file specifically for vector gep simplifications (test/Transforms/InstSimplify/vector_gep.ll), can you please add these new tests there? I find it easier to locate and fix bugs when related tests are co-located. A comment/link back to http://bugs.llvm.org/show_bug.cgi?id=32697 above the regression test also saves time for future bug hunting. Thanks!

Sure.

lib/Analysis/InstructionSimplify.cpp

   if (Ops.size() == 1)
     return Ops[0];
 
   // Compute the (pointer) type returned by the GEP instruction.
   Type *LastType = GetElementPtrInst::getIndexedType(SrcTy, Ops.slice(1));
   Type *GEPTy = PointerType::get(LastType, AS);
   if (VectorType *VT = dyn_cast<VectorType>(Ops[0]->getType()))
     GEPTy = VectorType::get(GEPTy, VT->getNumElements());
+  else if (VectorType *VT = dyn_cast<VectorType>(Ops[1]->getType()))
+    GEPTy = VectorType::get(GEPTy, VT->getNumElements());
 
   if (isa<UndefValue>(Ops[0]))
     return UndefValue::get(GEPTy);
 
   if (Ops.size() == 2) {
     // getelementptr P, 0 -> P.
     if (match(Ops[1], m_Zero()))
       return Ops[0];

test/Transforms/InstSimplify/gep-vector.ll

+; RUN: opt -instsimplify -S %s | FileCheck %s
+
+; CHECK-LABEL: tinkywinky(
+; CHECK-NEXT: ret <4 x i8*> undef
+define <4 x i8*> @tinkywinky() {
+  %patatino = getelementptr i8, i8* undef, <4 x i64> undef
+  ret <4 x i8*> %patatino
+}
+
+; CHECK-LABEL: dipsy(
+; CHECK-NEXT: ret <4 x i8*> undef
+define <4 x i8*> @dipsy() {
+  %patatino = getelementptr i8, <4 x i8 *> undef, <4 x i64> undef
+  ret <4 x i8*> %patatino
+}
+
+; CHECK-LABEL: laalaa(
+; CHECK-NEXT: ret <4 x i8*> undef
+define <4 x i8*> @laalaa() {
+  %patatino = getelementptr i8, <4 x i8 *> undef, i64 undef
+  ret <4 x i8*> %patatino
+}