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

[Owen Anderson 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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resistor wrote:

I tested initializing it in `initializeBase`, as we do for `IntSize`. The problem with doing it there is that we lack access to the `DataLayout`, so the best we can do would be to default to `Triple::getArchPointerBitWidth()`, which wouldn't represent an improvement on the status quo.

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