[compiler-rt] [sanitizer-common] Improve mach_vm_region_recurse error handling (PR #158670)

[Dan Blackwell via llvm-commits]

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@@ -1265,17 +1265,34 @@ uptr FindAvailableMemoryRange(uptr size, uptr alignment, uptr left_padding,
     kr = mach_vm_region_recurse(mach_task_self(), &address, &vmsize, &depth,
                                 (vm_region_info_t)&vminfo, &count);
 
-    // There are cases where going beyond the processes' max vm does
-    // not return KERN_INVALID_ADDRESS so we check for going beyond that
-    // max address as well.
-    if (kr == KERN_INVALID_ADDRESS || address > max_vm_address) {
+    if (kr == KERN_SUCCESS) {
+      // There are cases where going beyond the processes' max vm does
+      // not return KERN_INVALID_ADDRESS so we check for going beyond that
+      // max address as well.
+      if (address > max_vm_address) {
+        address = max_vm_address;
+        kr = -1;  // break after this iteration.
+      }
+
+      if (max_occupied_addr)
+        *max_occupied_addr = address + vmsize;
+    } else if (kr == KERN_INVALID_ADDRESS) {
       // No more regions beyond "address", consider the gap at the end of VM.
       address = max_vm_address;
-      vmsize = 0;
-      kr = -1;  // break after this iteration.
+
+      // We will break after this iteration anyway since kr != KERN_SUCCESS
+    } else if (kr == KERN_DENIED) {
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DanBlackwell wrote:

I agree this feels a little clunky, but the point about the `else` here being equivalent to the `default` case of a switch is why I think the current layout is fine. And there are enough comments here to understand _why_ we're setting the different variables.

https://github.com/llvm/llvm-project/pull/158670