[RelLookupTableConverter] Bail on invalid pointer size (x32)

[nikic]

Summary

The RelLookupTableConverter pass currently only supports 64-bit pointers. This is currently enforced using an isArch64Bit() check on the target triple. However, we consider x32 to be a 64-bit target, even though the pointers are 32-bit. (And independently of that specific example, there may be address spaces with different pointer sizes.)

As such, add an additional guard for the size of the pointers that are actually part of the lookup table.

[leonardchan]

LGTM pending any comments @gulfem may have

[gulfem]

Thanks @nikic, LGTM.

llvm/lib/Transforms/Utils/RelLookupTableConverter.cpp

static bool shouldConvertToRelLookupTable(Module &M, GlobalVariable &GV) {
   // its elements should have internal linkage and be dso_local, which means
   // that they should resolve to symbols within the same linkage unit.
   if (!GV.hasLocalLinkage() ||
       !GV.isDSOLocal() ||
       !GV.isImplicitDSOLocal())
     return false;
 
   ConstantArray *Array = dyn_cast<ConstantArray>(GV.getInitializer());
-  // If values are not pointers, do not generate a relative lookup table.
-  if (!Array || !Array->getType()->getElementType()->isPointerTy())
+  if (!Array)
     return false;
 
+  // If values are not 64-bit pointers, do not generate a relative lookup table.
   const DataLayout &DL = M.getDataLayout();
+  Type *ElemType = Array->getType()->getElementType();
+  if (!ElemType->isPointerTy() || DL.getPointerTypeSizeInBits(ElemType) != 64)
+    return false;
+
   for (const Use &Op : Array->operands()) {
     Constant *ConstOp = cast<Constant>(&Op);
     GlobalValue *GVOp;
     APInt Offset;
 
     // If an operand is not a constant offset from a lookup table,
     // do not generate a relative lookup table.
     if (!IsConstantOffsetFromGlobal(ConstOp, GVOp, Offset, DL))

llvm/test/Transforms/RelLookupTableConverter/X86/gnux32.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=rel-lookup-table-converter -relocation-model=pic -S | FileCheck %s
+; REQUIRES: x86-registered-target
+
+target datalayout = "e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnux32"
+
+@a = internal constant i32 0, align 4
+@b = internal constant i32 0, align 4
+@c = internal constant i32 0, align 4
+
+@table = private unnamed_addr constant [3 x ptr] [ptr @a, ptr @b, ptr @c]
+
+define ptr @test(i32 %cond) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:    [[SWITCH_GEP:%.*]] = getelementptr inbounds [3 x ptr], ptr @table, i32 0, i32 [[COND:%.*]]
+; CHECK-NEXT:    [[SWITCH_LOAD:%.*]] = load ptr, ptr [[SWITCH_GEP]], align 8
+; CHECK-NEXT:    ret ptr [[SWITCH_LOAD]]
+;
+  %switch.gep = getelementptr inbounds [3 x ptr], ptr @table, i32 0, i32 %cond
+  %switch.load = load ptr, ptr %switch.gep, align 8
+  ret ptr %switch.load
+}