[compiler-rt] [win/asan] Search both higher and lower in AllocateTrampolineRegion (PR #114212)

[Reid Kleckner via llvm-commits]

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@@ -340,32 +347,66 @@ struct TrampolineMemoryRegion {
   uptr max_size;
 };
 
-UNUSED static const uptr kTrampolineScanLimitRange = 1ull << 31;  // 2 gig
+UNUSED static const uptr kTrampolineRangeLimit = 1ull << 31;  // 2 gig
 static const int kMaxTrampolineRegion = 1024;
 static TrampolineMemoryRegion TrampolineRegions[kMaxTrampolineRegion];
 
-static void *AllocateTrampolineRegion(uptr image_address, size_t granularity) {
-#if SANITIZER_WINDOWS64
-  uptr address = image_address;
-  uptr scanned = 0;
-  while (scanned < kTrampolineScanLimitRange) {
+static void *AllocateTrampolineRegion(uptr min_addr, uptr max_addr,
+                                      uptr func_addr, size_t granularity) {
+#  if SANITIZER_WINDOWS64
+  // Clamp {min,max}_addr to the accessible address space.
+  SYSTEM_INFO system_info;
+  ::GetSystemInfo(&system_info);
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rnk wrote:

The call site here calls `GetMmapGranularity`, which also calls `GetSystemInfo`. Can we do `GetSystemInfo` once outside the loop, and store this information about the address space (mmap_granularity, addrspace_start, addrspace_end) in global variables? The performance gain is marginal, it's mostly to have fewer parameters and locals in this function.

https://github.com/llvm/llvm-project/pull/114212