[SPIRV] Get pointer size from datalayout (#66096)

Get the pointer size from the datalayout via the TargetMachine and
remove the helper function that hardcoded it. This fixes an issue caused
by mismatched pointer sizes between the two for logical SPIR-V, since
the computePointerSize function still defaulted to 32-bit ptr sizes.

Author: sudonatalie

llvm/lib/Target/SPIRV/SPIRVSubtarget.cpp

@@ -47,28 +47,14 @@ static bool isAtLeastVer(uint32_t Target, uint32_t VerToCompareTo) {
   return Target == 0 || Target >= VerToCompareTo;
 }
 
-static unsigned computePointerSize(const Triple &TT) {
-  const auto Arch = TT.getArch();
-  // TODO: unify this with pointers legalization.
-  assert(TT.isSPIRV());
-
-  if (Arch == Triple::spirv64)
-    return 64;
-
-  // TODO: this probably needs to be revisited:
-  //  AFAIU Logical SPIR-V has no pointer size. So falling-back on ID size.
-  //  Addressing mode can change how some pointers are handled
-  //  (PhysicalStorageBuffer64).
-  return 32;
-}
-
 SPIRVSubtarget::SPIRVSubtarget(const Triple &TT, const std::string &CPU,
                                const std::string &FS,
                                const SPIRVTargetMachine &TM)
     : SPIRVGenSubtargetInfo(TT, CPU, /*TuneCPU=*/CPU, FS),
-      PointerSize(computePointerSize(TT)), SPIRVVersion(0), OpenCLVersion(0),
-      InstrInfo(), FrameLowering(initSubtargetDependencies(CPU, FS)),
-      TLInfo(TM, *this), TargetTriple(TT) {
+      PointerSize(TM.getPointerSizeInBits(/* AS= */ 0)), SPIRVVersion(0),
+      OpenCLVersion(0), InstrInfo(),
+      FrameLowering(initSubtargetDependencies(CPU, FS)), TLInfo(TM, *this),
+      TargetTriple(TT) {
   // The order of initialization is important.
   initAvailableExtensions();
   initAvailableExtInstSets();