[llvm] TargetLibraryInfo: Use pointer index size to determine getSizeTSize(). (PR #118747)

[Sergei Barannikov via llvm-commits]

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@@ -1465,13 +1465,19 @@ unsigned TargetLibraryInfoImpl::getSizeTSize(const Module &M) const {
 
   // Historically LLVM assume that size_t has same size as intptr_t (hence
   // deriving the size from sizeof(int*) in address space zero). This should
-  // work for most targets. For future consideration: DataLayout also implement
-  // getIndexSizeInBits which might map better to size_t compared to
-  // getPointerSizeInBits. Hard coding address space zero here might be
-  // unfortunate as well. Maybe getDefaultGlobalsAddressSpace() or
-  // getAllocaAddrSpace() is better.
+  // work for most targets. For future consideration: Hard coding address space
+  // zero here might be unfortunate. Maybe getMaxIndexSizeInBits() is better.
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s-barannikov wrote:

Probably not a big difference, but...
`size_t` is a C language concept not directly related to data layout, which is more of a machine concept.
The size of `size_t` can as well be less than whatever `get*IndexSizeInBits` returns.
Would it make more sense to handle `size_t` similar to `int`? (See `getIntSize`, `setIntSize`.)


https://github.com/llvm/llvm-project/pull/118747