[SimplifyCFG] Bail out on vector GEPs in passingValueIsAlwaysUndefined (#142526)

Closes #142522.

Author: dtcxzyw

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -8108,6 +8108,7 @@ bool SimplifyCFGOpt::simplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
 
 /// Check if passing a value to an instruction will cause undefined behavior.
 static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValueMayBeModified) {
+  assert(V->getType() == I->getType() && "Mismatched types");
   Constant *C = dyn_cast<Constant>(V);
   if (!C)
     return false;
@@ -8165,6 +8166,10 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValu
     // Look through GEPs. A load from a GEP derived from NULL is still undefined
     if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User))
       if (GEP->getPointerOperand() == I) {
+        // The type of GEP may differ from the type of base pointer.
+        // Bail out on vector GEPs, as they are not handled by other checks.
+        if (GEP->getType()->isVectorTy())
+          return false;
         // The current base address is null, there are four cases to consider:
         // getelementptr (TY, null, 0)                 -> null
         // getelementptr (TY, null, not zero)          -> may be modified

llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll

@@ -244,6 +244,7 @@ declare ptr @fn_nonnull_arg(ptr nonnull %p)
 declare ptr @fn_noundef_arg(ptr noundef %p)
 declare ptr @fn_ptr_arg(ptr)
 declare ptr @fn_ptr_arg_nounwind_willreturn(ptr) nounwind willreturn
+declare void @fn_arg_vec(<2 x ptr>)
 
 define void @test9(i1 %X, ptr %Y) {
 ; CHECK-LABEL: @test9(
@@ -917,6 +918,25 @@ bb5:                                              ; preds = %bb3, %bb
   ret i32 %i7
 }
 
+define void @test9_gep_splat(i1 %X, ptr %Y) {
+; CHECK-LABEL: @test9_gep_splat(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[X:%.*]], ptr null, ptr [[Y:%.*]]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i8, ptr [[SPEC_SELECT]], <2 x i64> zeroinitializer
+; CHECK-NEXT:    call void @fn_arg_vec(<2 x ptr> [[GEP]])
+; CHECK-NEXT:    ret void
+;
+entry:
+  br i1 %X, label %if, label %else
+if:
+  br label %else
+else:
+  %phi = phi ptr [ %Y, %entry ], [ null, %if ]
+  %gep = getelementptr i8, ptr %phi, <2 x i64> zeroinitializer
+  call void @fn_arg_vec(<2 x ptr> %gep)
+  ret void
+}
+
 declare void @side.effect()
 declare i8 @get.i8()