[InstCombine] Handle vector gep with scalar argument in evaluateInDifferentElementOrder

[uabelho]

Summary

This fixes PR41270.

The recursive function evaluateInDifferentElementOrder expects to be called
on a vector Value, so when we call it on a vector GEP's arguments, we must
first check that the argument is indeed a vector.

[spatel]

LGTM, but we can reduce the test (also please use 'utils/update_test_checks.py' to auto-generate the FileCheck lines):

define <4 x i16*> @PR41270([4 x i16]* %x) {
  %ins = insertelement <4 x [4 x i16]*> undef, [4 x i16]* %x, i32 0
  %splat = shufflevector <4 x [4 x i16]*> %ins, <4 x [4 x i16]*> undef, <4 x i32> zeroinitializer
  %t2 = getelementptr inbounds [4 x i16], <4 x [4 x i16]*> %splat, i32 0, i32 3
  %t3 = extractelement <4 x i16*> %t2, i32 3
  %ins2 = insertelement <4 x i16*> undef, i16* %t3, i32 0
  ret <4 x i16*> %ins2
}

[uabelho]

Great! I'll update the test and submit in a little bit.

Thanks!

lib/Transforms/InstCombine/InstCombineVectorOps.cpp

switch (I->getOpcode()) {
     case Instruction::SIToFP:
     case Instruction::FPTrunc:
     case Instruction::FPExt:
     case Instruction::Select:
     case Instruction::GetElementPtr: {
       SmallVector<Value*, 8> NewOps;
       bool NeedsRebuild = (Mask.size() != I->getType()->getVectorNumElements());
       for (int i = 0, e = I->getNumOperands(); i != e; ++i) {
-        Value *V = evaluateInDifferentElementOrder(I->getOperand(i), Mask);
+        Value *V;
+        // Recursively call evaluateInDifferentElementOrder on vector arguments
+        // as well. E.g. GetElementPtr may have scalar operands even if the
+        // return value is a vector, so we need to examine the operand type.
+        if (I->getOperand(i)->getType()->isVectorTy())
+          V = evaluateInDifferentElementOrder(I->getOperand(i), Mask);
+        else
+          V = I->getOperand(i);
         NewOps.push_back(V);
         NeedsRebuild |= (V != I->getOperand(i));
       }
       if (NeedsRebuild) {
         return buildNew(I, NewOps);
       }
       return I;
     }

test/Transforms/InstCombine/vec_gep_scalar_arg.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -instcombine -S < %s | FileCheck %s
+
+define <4 x i16*> @PR41270([4 x i16]* %x) {
+; CHECK-LABEL: @PR41270(
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <4 x [4 x i16]*> undef, [4 x i16]* [[X:%.*]], i32 0
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds [4 x i16], <4 x [4 x i16]*> [[TMP1]], i64 0, i64 3
+; CHECK-NEXT:    ret <4 x i16*> [[TMP2]]
+;
+  %ins = insertelement <4 x [4 x i16]*> undef, [4 x i16]* %x, i32 0
+  %splat = shufflevector <4 x [4 x i16]*> %ins, <4 x [4 x i16]*> undef, <4 x i32> zeroinitializer
+  %t2 = getelementptr inbounds [4 x i16], <4 x [4 x i16]*> %splat, i32 0, i32 3
+  %t3 = extractelement <4 x i16*> %t2, i32 3
+  %ins2 = insertelement <4 x i16*> undef, i16* %t3, i32 0
+  ret <4 x i16*> %ins2
+}