Fix incorrect conditional predicting loop count

Author: cjappl

compiler-rt/test/rtsan/unbound_loop.cpp

@@ -0,0 +1,48 @@
+// RUN: %clangxx -fsanitize=realtime %s -o %t -O3
+// RUN: not %run %t 2>&1 | FileCheck %s --allow-empty
+// RUN: %clangxx -fsanitize=realtime %s -o %t -O2
+// RUN: not %run %t 2>&1 | FileCheck %s --allow-empty
+// RUN: %clangxx -fsanitize=realtime %s -o %t -O1
+// RUN: not %run %t 2>&1 | FileCheck %s --allow-empty
+
+// RUN: %clangxx -fsanitize=realtime %s -o %t -O0
+// RUN: not %run %t 2>&1 | FileCheck %s --allow-empty
+
+// UNSUPPORTED: ios
+
+// Intent: Ensure basic bound audio loops don't trigger rtsan.
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <assert.h>
+
+
+void BadScalarEvolution(int* buffer, int sample_count, int channel_count) [[clang::nonblocking]] {
+
+  int sample = 0;
+  while (sample < sample_count) {
+    int channel = 0;
+    while (channel < channel_count) {
+      buffer[sample * channel_count + channel] = sample;
+      channel++;
+    }
+    sample++;
+
+    // NOTE! Here is the "bug" that causes the loop to be unbounded.
+    sample_count++;
+  }
+}
+
+int main() {
+  const int sample_count = 10;
+  const int channel_count = 2;
+  int buffer[channel_count * sample_count];
+
+  BadScalarEvolution(buffer, sample_count, channel_count);
+
+  return 0;
+}
+
+// CHECK: {{.*Real-time violation.*}}
+// CHECK-NEXT {{.*BadScalarEvolution.*}}

llvm/lib/Transforms/Instrumentation/RealtimeSanitizer.cpp

@@ -84,7 +84,7 @@ PreservedAnalyses RealtimeSanitizerLoopPass::run(Loop &L, LoopAnalysisManager &A
   assert(F && "Loop has no parent function");
 
   const bool HasNoExits = L.hasNoExitBlocks();
-  const bool CannotPredictLoopCount = isa<SCEVCouldNotCompute>(AR.SE.getConstantMaxBackedgeTakenCount(&L)) &&
+  const bool CannotPredictLoopCount = isa<SCEVCouldNotCompute>(AR.SE.getConstantMaxBackedgeTakenCount(&L)) ||
         isa<SCEVCouldNotCompute>(AR.SE.getBackedgeTakenCount(&L));
   const bool LoopIsPotentiallyUnbound = HasNoExits || CannotPredictLoopCount;