TargetLibraryInfo: Use pointer index size to determine getSizeTSize().

When using non-integral pointer types, such as on CHERI targets, size_t is equivalent
to the index size, which is allowed to be smaller than the size of the pointer.

Author: resistor

llvm/lib/Analysis/TargetLibraryInfo.cpp

@@ -1465,13 +1465,10 @@ 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.
   unsigned AddressSpace = 0;
-  return M.getDataLayout().getPointerSizeInBits(AddressSpace);
+  return M.getDataLayout().getIndexSizeInBits(AddressSpace);
 }
 
 TargetLibraryInfoWrapperPass::TargetLibraryInfoWrapperPass()

llvm/test/Transforms/InstCombine/stdio-custom-dl.ll

@@ -8,11 +8,10 @@ target datalayout = "e-m:o-p:40:64:64:32-i64:64-f80:128-n8:16:32:64-S128"
 @.str.1 = private unnamed_addr constant [2 x i8] c"w\00", align 1
 @.str.2 = private unnamed_addr constant [4 x i8] c"str\00", align 1
 
-; Check fwrite is generated with arguments of ptr size, not index size
 define internal void @fputs_test_custom_dl() {
 ; CHECK-LABEL: @fputs_test_custom_dl(
 ; CHECK-NEXT:    [[CALL:%.*]] = call ptr @fopen(ptr nonnull @.str, ptr nonnull @.str.1)
-; CHECK-NEXT:    [[TMP1:%.*]] = call i40 @fwrite(ptr nonnull @.str.2, i40 3, i40 1, ptr [[CALL]])
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @fwrite(ptr nonnull @.str.2, i32 3, i32 1, ptr %call)
 ; CHECK-NEXT:    ret void
 ;
   %call = call ptr @fopen(ptr @.str, ptr @.str.1)

llvm/test/Transforms/MergeICmps/X86/distinct-index-width-crash.ll

@@ -8,15 +8,15 @@ target triple = "x86_64"
 target datalayout = "e-p:64:64:64:32"
 
 ; Define a cunstom data layout that has index width < pointer width
-; and make sure that doesn't mreak anything
+; and make sure that doesn't break anything
 define void @fat_ptrs(ptr dereferenceable(16) %a, ptr dereferenceable(16) %b) {
 ; CHECK-LABEL: @fat_ptrs(
 ; CHECK-NEXT:  bb0:
 ; CHECK-NEXT:    [[PTR_A1:%.*]] = getelementptr inbounds [2 x i64], ptr [[A:%.*]], i32 0, i32 1
 ; CHECK-NEXT:    [[PTR_B1:%.*]] = getelementptr inbounds [2 x i64], ptr [[B:%.*]], i32 0, i32 1
 ; CHECK-NEXT:    br label %"bb1+bb2"
 ; CHECK:       "bb1+bb2":
-; CHECK-NEXT:    [[MEMCMP:%.*]] = call i32 @memcmp(ptr [[A]], ptr [[B]], i64 16)
+; CHECK-NEXT:    [[MEMCMP:%.*]] = call i32 @memcmp(ptr [[A]], ptr [[B]], i32 16)
 ; CHECK-NEXT:    [[TMP0:%.*]] = icmp eq i32 [[MEMCMP]], 0
 ; CHECK-NEXT:    br label [[BB3:%.*]]
 ; CHECK:       bb3: