[clang] ad1b9da - Prepend "__uniq" to symbol names hash with -funique-internal-linkage-names.

[Sriraman Tallam via cfe-commits]

Author: Sriraman Tallam
Date: 2020-10-26T14:24:28-07:00
New Revision: ad1b9daa4bf40c1907794fd5de7807aad1f0553c

URL: https://github.com/llvm/llvm-project/commit/ad1b9daa4bf40c1907794fd5de7807aad1f0553c
DIFF: https://github.com/llvm/llvm-project/commit/ad1b9daa4bf40c1907794fd5de7807aad1f0553c.diff

LOG: Prepend "__uniq" to symbol names hash with -funique-internal-linkage-names.

Prepend the module name hash with a fixed string ".__uniq." which helps tools
that consume sampled profiles and attribute it to functions to understand
that this symbol belongs to a unique internal linkage type symbol.

Symbols with suffixes can result from various optimizations in the compiler.
Function Multiversioning, function splitting, parameter constant propogation,
unique internal linkage names.

External tools like sampled profile aggregators combine profiles from multiple
runs of a binary. They use various heuristics with symbols that have suffixes
to try and attribute the profile to the right function instance. For instance
multi-versioned symbols like foo.avx, foo.sse4.2, etc even though different
should be attributed to the same source function if a single function is
versioned, using attribute target_clones (supported in GCC but yet to land in
LLVM). Similarly, functions that are split (split part having a .cold suffix)
could have profiles for both the original and split symbols but would be
aggregated and attributed to the original function that was split.

Unique internal linkage functions however have different source instances and
the aggregator must not put them together but attribute it to the appropriate
function instance. To be sure that we are dealing with a symbol of a unique
internal linkage function, we would like to prepend the hash with a known
string ".__uniq." which these tools can check to understand the suffix type.

Differential Revision: https://reviews.llvm.org/D89617

Added: 
    

Modified: 
    clang/test/CodeGen/unique-internal-linkage-names.cpp
    llvm/lib/Transforms/Utils/UniqueInternalLinkageNames.cpp
    llvm/test/Transforms/UniqueInternalLinkageNames/unique_symbol_names.ll

Removed: 
    


################################################################################
diff  --git a/clang/test/CodeGen/unique-internal-linkage-names.cpp b/clang/test/CodeGen/unique-internal-linkage-names.cpp
index 6bef338b5f1d..3ad3bdc9f1bb 100644
--- a/clang/test/CodeGen/unique-internal-linkage-names.cpp
+++ b/clang/test/CodeGen/unique-internal-linkage-names.cpp
@@ -53,15 +53,15 @@ int mver_call() {
 // PLAIN: define weak_odr i32 ()* @_ZL4mverv.resolver()
 // PLAIN: define internal i32 @_ZL4mverv()
 // PLAIN: define internal i32 @_ZL4mverv.sse4.2()
-// UNIQUE: @_ZL4glob.{{[0-9a-f]+}} = internal global
-// UNIQUE: @_ZZ8retAnonMvE5fGlob.{{[0-9a-f]+}} = internal global
-// UNIQUE: @_ZN12_GLOBAL__N_16anon_mE.{{[0-9a-f]+}} = internal global
-// UNIQUE: define internal i32 @_ZL3foov.{{[0-9a-f]+}}()
-// UNIQUE: define internal i32 @_ZN12_GLOBAL__N_14getMEv.{{[0-9a-f]+}}
+// UNIQUE: @_ZL4glob.__uniq.{{[0-9a-f]+}} = internal global
+// UNIQUE: @_ZZ8retAnonMvE5fGlob.__uniq.{{[0-9a-f]+}} = internal global
+// UNIQUE: @_ZN12_GLOBAL__N_16anon_mE.__uniq.{{[0-9a-f]+}} = internal global
+// UNIQUE: define internal i32 @_ZL3foov.__uniq.{{[0-9a-f]+}}()
+// UNIQUE: define internal i32 @_ZN12_GLOBAL__N_14getMEv.__uniq.{{[0-9a-f]+}}
 // UNIQUE: define weak_odr i32 ()* @_ZL4mverv.resolver()
-// UNIQUE: define internal i32 @_ZL4mverv.{{[0-9a-f]+}}()
-// UNIQUE: define internal i32 @_ZL4mverv.sse4.2.{{[0-9a-f]+}}
-// UNIQUEO1: define internal i32 @_ZL3foov.{{[0-9a-f]+}}()
+// UNIQUE: define internal i32 @_ZL4mverv.__uniq.{{[0-9a-f]+}}()
+// UNIQUE: define internal i32 @_ZL4mverv.sse4.2.__uniq.{{[0-9a-f]+}}
+// UNIQUEO1: define internal i32 @_ZL3foov.__uniq.{{[0-9a-f]+}}()
 // UNIQUEO1: define weak_odr i32 ()* @_ZL4mverv.resolver()
-// UNIQUEO1: define internal i32 @_ZL4mverv.{{[0-9a-f]+}}()
-// UNIQUEO1: define internal i32 @_ZL4mverv.sse4.2.{{[0-9a-f]+}}
+// UNIQUEO1: define internal i32 @_ZL4mverv.__uniq.{{[0-9a-f]+}}()
+// UNIQUEO1: define internal i32 @_ZL4mverv.sse4.2.__uniq.{{[0-9a-f]+}}

diff  --git a/llvm/lib/Transforms/Utils/UniqueInternalLinkageNames.cpp b/llvm/lib/Transforms/Utils/UniqueInternalLinkageNames.cpp
index 5b58548e54dc..385bf8bb429a 100644
--- a/llvm/lib/Transforms/Utils/UniqueInternalLinkageNames.cpp
+++ b/llvm/lib/Transforms/Utils/UniqueInternalLinkageNames.cpp
@@ -27,7 +27,9 @@ static bool uniqueifyInternalLinkageNames(Module &M) {
   Md5.final(R);
   SmallString<32> Str;
   llvm::MD5::stringifyResult(R, Str);
-  std::string ModuleNameHash = (Twine(".") + Twine(Str)).str();
+  // Prepend "__uniq" before the hash for tools like profilers to understand that
+  // this symbol is of internal linkage type.
+  std::string ModuleNameHash = (Twine(".__uniq.") + Twine(Str)).str();
   bool Changed = false;
 
   // Append the module hash to all internal linkage functions.

diff  --git a/llvm/test/Transforms/UniqueInternalLinkageNames/unique_symbol_names.ll b/llvm/test/Transforms/UniqueInternalLinkageNames/unique_symbol_names.ll
index e2ff4aed6e29..9a7828c831c3 100644
--- a/llvm/test/Transforms/UniqueInternalLinkageNames/unique_symbol_names.ll
+++ b/llvm/test/Transforms/UniqueInternalLinkageNames/unique_symbol_names.ll
@@ -9,5 +9,5 @@ entry:
   ret i32 0
 }
 
-; CHECK: @glob.6ae72bb15a7d1834b42ae042a58f7a4d = internal global
-; CHECK: define internal i32 @foo.6ae72bb15a7d1834b42ae042a58f7a4d()
+; CHECK: @glob.__uniq.6ae72bb15a7d1834b42ae042a58f7a4d = internal global
+; CHECK: define internal i32 @foo.__uniq.6ae72bb15a7d1834b42ae042a58f7a4d()