[PATCH] D55643: [llvm] Address base discriminator overflow in X86DiscriminateMemOps

[Mircea Trofin via Phabricator via llvm-commits]

mtrofin created this revision.
mtrofin added a reviewer: davidxl.
Herald added subscribers: llvm-commits, aprantl.

Macros are expanded on a single line. In case of large expansions,
with sufficiently many instructions with memory operands (and when
-fdebug-info-for-profiling is requested), we may be unable to generate
new base discriminator values - new values overflow (base
discriminators may not be larger than 2^12).

This CL warns instead of asserting in such a case. A subsequent CL
will add APIs to check for overflow before creating new debug info.


Repository:
  rL LLVM

https://reviews.llvm.org/D55643

Files:
  lib/Target/X86/X86DiscriminateMemOps.cpp


Index: lib/Target/X86/X86DiscriminateMemOps.cpp
===================================================================
--- lib/Target/X86/X86DiscriminateMemOps.cpp
+++ lib/Target/X86/X86DiscriminateMemOps.cpp
@@ -24,6 +24,8 @@
 #include "llvm/Transforms/IPO/SampleProfile.h"
 using namespace llvm;
 
+#define DEBUG_TYPE "x86-discriminate-memops"
+
 namespace {
 
 using Location = std::pair<StringRef, unsigned>;
@@ -114,9 +116,18 @@
         Changed = true;
         const std::pair<DenseSet<unsigned>::iterator, bool> MustInsert =
             Set.insert(DI->getBaseDiscriminator());
-        (void)MustInsert; // silence warning.
-        assert(MustInsert.second &&
-               "New discriminator shouldn't be present in set");
+        // FIXME (mtrofin): check if the to-be inserted base discriminator can
+        // be added. This requires a new API on DILocation.
+        // The assumption is that this scenario is infrequent/OK not to support.
+        // If evidence points otherwise, we can explore synthesize unique DIs by
+        // adding fake line numbers.
+        if (!MustInsert.second) {
+          LLVM_DEBUG(dbgs()
+                     << "Unable to create a unique discriminator in "
+                     << DI->getFilename() << " Line: " << DI->getLine()
+                     << " Column: " << DI->getColumn()
+                     << ". This is likely due to a large macro expansion.\n");
+        }
       }
 
       // Bump the reference DI to avoid cramming discriminators on line 0.


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