[llvm] Address base discriminator overflow in X86DiscriminateMemOps
Summary:
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.
See https://bugs.llvm.org/show_bug.cgi?id=39890
Reviewers: davidxl, wmi, gbedwell
Reviewed By: davidxl
Subscribers: aprantl, llvm-commits
Differential Revision: https://reviews.llvm.org/D55643
llvm-svn: 349075
diff --git a/llvm/lib/Target/X86/X86DiscriminateMemOps.cpp b/llvm/lib/Target/X86/X86DiscriminateMemOps.cpp
index 4ab32ab..5653bab 100644
--- a/llvm/lib/Target/X86/X86DiscriminateMemOps.cpp
+++ b/llvm/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.