UniqSupply: Use full range of machine word

Currently uniques are 32-bits wide. 8 of these bits are for the unique
class, leaving only 24 for the unique number itself. This seems
dangerously small for a large project. Let's use the full range of the
native machine word.

We also add (now largely unnecessary) overflow check to ensure that the
unique number doesn't overflow.

Test Plan: Validate

Reviewers: simonmar, austin, niteria

Reviewed By: niteria

Subscribers: mpickering, thomie

Differential Revision: https://phabricator.haskell.org/D2844

GHC Trac Issues: #12944

1 files changed, 21 insertions, 4 deletions

diff --git a/compiler/cbits/genSym.c b/compiler/cbits/genSym.c
index 70ea417c4b..725a310253 100644
--- a/compiler/cbits/genSym.c
+++ b/compiler/cbits/genSym.c
@@ -1,18 +1,35 @@
-
+#include <assert.h>
 #include "Rts.h"
+#include "Unique.h"
 
 static HsInt GenSymCounter = 0;
 static HsInt GenSymInc = 1;
 
+#define UNIQUE_MASK ((1ULL << UNIQUE_BITS) - 1)
+
+STATIC_INLINE void checkUniqueRange(HsInt u STG_UNUSED) {
+#if DEBUG
+    // Uh oh! We will overflow next time a unique is requested.
+    assert(h != UNIQUE_MASK);
+#endif
+}
+
 HsInt genSym(void) {
 #if defined(THREADED_RTS)
     if (n_capabilities == 1) {
-        return GenSymCounter = (GenSymCounter + GenSymInc) & 0xFFFFFF;
+        GenSymCounter = (GenSymCounter + GenSymInc) & UNIQUE_MASK;
+        checkUniqueRange(GenSymCounter);
+        return GenSymCounter;
     } else {
-        return atomic_inc((StgWord *)&GenSymCounter, GenSymInc) & 0xFFFFFF;
+        HsInt n = atomic_inc((StgWord *)&GenSymCounter, GenSymInc)
+          & UNIQUE_MASK;
+        checkUniqueRange(n);
+        return n;
     }
 #else
-    return GenSymCounter = (GenSymCounter + GenSymInc) & 0xFFFFFF;
+    GenSymCounter = (GenSymCounter + GenSymInc) & UNIQUE_MASK;
+    checkUniqueRange(GenSymCounter);
+    return GenSymCounter;
 #endif
 }