Add hierarchical discriminator multiplicity support

gcov_discriminator_encoding.h

@@ -0,0 +1,57 @@
+// Discriminator encoding utilities for AutoFDO
+// Similar to LLVM's discriminator encoding scheme
+//
+// Discriminator format: [Base:8][Multiplicity:7][CopyID:11][Unused:6]
+// - Base discriminator (bits 0-7): Distinguishes instructions at same line
+// - Multiplicity (bits 8-14): Duplication factor for unrolling/vectorization  
+// - CopyID (bits 15-25): Unique identifier for code copies
+// - Unused (bits 26-31): Reserved
+
+#ifndef AUTOFDO_DISCRIMINATOR_ENCODING_H_
+#define AUTOFDO_DISCRIMINATOR_ENCODING_H_
+
+#include <cstdint>
+
+namespace devtools_crosstool_autofdo {
+
+// Extract base discriminator (bits 0-7)
+inline uint32_t GetBaseDiscriminator(uint32_t discriminator) {
+  return discriminator & 0xFF;
+}
+
+// Extract multiplicity/duplication factor (bits 8-14)
+// Returns 1 if multiplicity bits are 0 (no duplication)
+inline uint32_t GetMultiplicity(uint32_t discriminator) {
+  uint32_t mult = (discriminator >> 8) & 0x7F;
+  return (mult == 0) ? 1 : mult;
+}
+
+// Extract copy ID (bits 15-25)
+inline uint32_t GetCopyID(uint32_t discriminator) {
+  return (discriminator >> 15) & 0x7FF;
+}
+
+// Encode discriminator from components
+inline uint32_t EncodeDiscriminator(uint32_t base, uint32_t multiplicity,
+                                     uint32_t copy_id) {
+  // Validate ranges
+  if (base > 0xFF || multiplicity > 127 || copy_id > 0x7FF) {
+    return base;  // Fallback to just base if encoding fails
+  }
+  return base | (multiplicity << 8) | (copy_id << 15);
+}
+
+// Check if discriminator has multiplicity encoded
+inline bool HasMultiplicity(uint32_t discriminator) {
+  return GetMultiplicity(discriminator) > 1;
+}
+
+// Check if discriminator has copy ID encoded
+inline bool HasCopyID(uint32_t discriminator) {
+  return GetCopyID(discriminator) != 0;
+}
+
+}  // namespace devtools_crosstool_autofdo
+
+#endif  // AUTOFDO_DISCRIMINATOR_ENCODING_H_
+

source_info.h

@@ -11,6 +11,9 @@
 #include "base/macros.h"
 #if defined(HAVE_LLVM)
 #include "llvm/IR/DebugInfoMetadata.h"
+#else
+// Include discriminator encoding utilities only when LLVM is not available
+#include "gcov_discriminator_encoding.h"
 #endif
 
 namespace devtools_crosstool_autofdo {
@@ -49,7 +52,11 @@ struct SourceInfo {
                    discriminator)
              : discriminator));
 #else
-    return (static_cast<uint64_t>(line - start_line) << 32) | discriminator;
+    // Profile stores only base discriminator (bits 0-7).
+    uint32_t disc = use_discriminator_encoding 
+                    ? GetBaseDiscriminator(discriminator)
+                    : discriminator;
+    return (static_cast<uint64_t>(line - start_line) << 32) | disc;
 #endif
   }
 
@@ -59,7 +66,9 @@ struct SourceInfo {
     return llvm::DILocation::getDuplicationFactorFromDiscriminator(
         discriminator);
 #else
-    return 1;
+    // Only extract multiplicity if discriminator is non-zero
+    if (discriminator == 0) return 1;
+    return GetMultiplicity(discriminator);
 #endif
   }
 
@@ -79,6 +88,11 @@ struct SourceInfo {
   static constexpr uint32_t GenerateCompressedOffset(uint64_t Offset) {
     return static_cast<uint32_t>((Offset >> 16) | (Offset & 0xffff));
   }
+
+  // Return the full 64-bit offset for 32-bit hierarchical discriminators.
+  static constexpr uint64_t GenerateFullOffset(uint64_t Offset) {
+    return Offset;
+  }
 
   // Return the line number from the offset.
   static constexpr uint32_t GetLineNumberFromOffset(uint64_t Offset) {