[PATCH] D79121: Add nomerge function attribute to clang

[Zequan Wu via Phabricator via cfe-commits]

zequanwu created this revision.
zequanwu added a reviewer: rnk.
zequanwu added a project: clang.
Herald added a subscriber: cfe-commits.

Related to D78659 <https://reviews.llvm.org/D78659>


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D79121

Files:
  clang/include/clang/Basic/Attr.td
  clang/include/clang/Basic/AttrDocs.td
  clang/lib/CodeGen/CGCall.cpp
  clang/test/CodeGen/attr-nomerge.c
  clang/test/Misc/pragma-attribute-supported-attributes-list.test


Index: clang/test/Misc/pragma-attribute-supported-attributes-list.test
===================================================================
--- clang/test/Misc/pragma-attribute-supported-attributes-list.test
+++ clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -89,6 +89,7 @@
 // CHECK-NEXT: NoEscape (SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: NoInline (SubjectMatchRule_function)
 // CHECK-NEXT: NoInstrumentFunction (SubjectMatchRule_function)
+// CHECK-NEXT: NoMerge (SubjectMatchRule_function)
 // CHECK-NEXT: NoMicroMips (SubjectMatchRule_function)
 // CHECK-NEXT: NoMips16 (SubjectMatchRule_function)
 // CHECK-NEXT: NoSanitize (SubjectMatchRule_function, SubjectMatchRule_objc_method, SubjectMatchRule_variable_is_global)
Index: clang/test/CodeGen/attr-nomerge.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/attr-nomerge.c
@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 -S -emit-llvm %s -o - | FileCheck %s
+
+void bar() __attribute__((nomerge));
+
+void foo(int i) {
+    if (i == 5) {
+        bar();
+    }
+    else if (i == 7) {
+        bar();
+    }
+    bar();
+}
+// CHECK: attributes #1 = { nomerge {{.*}} }
+// CHECK: attributes #2 = { nomerge }
Index: clang/lib/CodeGen/CGCall.cpp
===================================================================
--- clang/lib/CodeGen/CGCall.cpp
+++ clang/lib/CodeGen/CGCall.cpp
@@ -1905,6 +1905,8 @@
       FuncAttrs.addAttribute(llvm::Attribute::NoDuplicate);
     if (TargetDecl->hasAttr<ConvergentAttr>())
       FuncAttrs.addAttribute(llvm::Attribute::Convergent);
+    if (TargetDecl->hasAttr<NoMergeAttr>())
+      FuncAttrs.addAttribute(llvm::Attribute::NoMerge);
 
     if (const FunctionDecl *Fn = dyn_cast<FunctionDecl>(TargetDecl)) {
       AddAttributesFromFunctionProtoType(
Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -350,6 +350,19 @@
   }];
 }
 
+def NoMergeDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+Calls to functions marked `nomerge` will not be merged during optimization.
+This attribute can be used to prevent the optimizer from obscuring the source
+location of certain calls. For example, it will prevent tail merging otherwise
+identical code sequences that raise an exception or terminate the program. Tail
+merging normally reduces the precision of source location information, making
+stack traces less useful for debugging. This attribute gives the user control
+over the tradeoff between code size and debug information precision.
+  }];
+}
+
 def AssertCapabilityDocs : Documentation {
   let Category = DocCatFunction;
   let Heading = "assert_capability, assert_shared_capability";
Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -1794,6 +1794,13 @@
   let Documentation = [Undocumented];
 }
 
+def NoMerge : InheritableAttr {
+  let Spellings = [Clang<"nomerge">];
+  let Subjects = SubjectList<[Function]>;
+  let Documentation = [NoMergeDocs];
+  let SimpleHandler = 1;
+}
+
 def NoInstrumentFunction : InheritableAttr {
   let Spellings = [GCC<"no_instrument_function">];
   let Subjects = SubjectList<[Function]>;


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