Recommit "[Support] change StringMap hash function from djbHash to xxHash"

This reverts commit 37eb9d13f891f7656f811516e765b929b169afe0.

Test failures have been fixed:

- ubsan failure fixed by 72eac42f21c0f45a27f3eaaff9364cbb5189b9e4
- warn-unsafe-buffer-usage-fixits-local-var-span.cpp fixed by
  03cc52dfd1dbb4a59b479da55e87838fb93d2067 (wasn't related)
- test-output-format.ll failure was spurious, build failed at
  https://lab.llvm.org/buildbot/#/builders/54/builds/3545 (b4431b2d945b6fc19b1a55ac6ce969a8e06e1e93)
  but passed at
  https://lab.llvm.org/buildbot/#/builders/54/builds/3546 (5ae99be0377248c74346096dc475af254a3fc799)
  which is before my revert
  https://github.com/llvm/llvm-project/compare/b4431b2d945b6fc19b1a55ac6ce969a8e06e1e93...5ae99be0377248c74346096dc475af254a3fc799

Original commit message:

    Depends on https://reviews.llvm.org/D142861.

    Alternative to https://reviews.llvm.org/D137601.

    xxHash is much faster than djbHash. This makes a simple Rust test case with a large constant string 10% faster to compile.

    Previous attempts at changing this hash function (e.g. https://reviews.llvm.org/D97396) had to be reverted due to breaking tests that depended on iteration order.
    No additional tests fail with this patch compared to `main` when running `check-all` with `-DLLVM_ENABLE_PROJECTS="all"` (on a Linux host), so I hope I found everything that needs to be changed.

    Differential Revision: https://reviews.llvm.org/D142862

1 files changed, 3 insertions, 3 deletions

diff --git a/llvm/lib/Support/StringMap.cpp b/llvm/lib/Support/StringMap.cpp
index 9b2f96fca2cd..cf8f0930459d 100644
--- a/llvm/lib/Support/StringMap.cpp
+++ b/llvm/lib/Support/StringMap.cpp
@@ -11,8 +11,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/StringMap.h"
-#include "llvm/Support/DJB.h"
 #include "llvm/Support/MathExtras.h"
+#include "llvm/Support/xxhash.h"
 
 using namespace llvm;
 
@@ -84,7 +84,7 @@ unsigned StringMapImpl::LookupBucketFor(StringRef Name) {
   // Hash table unallocated so far?
   if (NumBuckets == 0)
     init(16);
-  unsigned FullHashValue = djbHash(Name, 0);
+  unsigned FullHashValue = xxHash64(Name);
   unsigned BucketNo = FullHashValue & (NumBuckets - 1);
   unsigned *HashTable = getHashTable(TheTable, NumBuckets);
 
@@ -139,7 +139,7 @@ unsigned StringMapImpl::LookupBucketFor(StringRef Name) {
 int StringMapImpl::FindKey(StringRef Key) const {
   if (NumBuckets == 0)
     return -1; // Really empty table?
-  unsigned FullHashValue = djbHash(Key, 0);
+  unsigned FullHashValue = xxHash64(Key);
   unsigned BucketNo = FullHashValue & (NumBuckets - 1);
   unsigned *HashTable = getHashTable(TheTable, NumBuckets);