[PATCH] D30727: Don't merge global constants with !type

[Evgeniy Stepanov via Phabricator via llvm-commits]

eugenis created this revision.

!type metadata can not be dropped. An alternative to this is adding
!type metadata from the replaced globals to the replacement, but that
may weaken type tests and make them slower at the same tim


Repository:
  rL LLVM

https://reviews.llvm.org/D30727

Files:
  lib/Transforms/IPO/ConstantMerge.cpp
  test/Transforms/ConstantMerge/dont-merge.ll


Index: test/Transforms/ConstantMerge/dont-merge.ll
===================================================================
--- test/Transforms/ConstantMerge/dont-merge.ll
+++ test/Transforms/ConstantMerge/dont-merge.ll
@@ -42,3 +42,41 @@
   call void asm sideeffect "T3A, T3B",""() ; invisible use of T3A and T3B
   ret void
 }
+
+; Don't merge constants with !type annotations.
+
+ at T4A1 = internal constant i32 2, !type !0
+ at T4A2 = internal unnamed_addr constant i32 2, !type !1
+
+ at T4B1 = internal constant i32 3, !type !0
+ at T4B2 = internal unnamed_addr constant i32 3, !type !0
+
+ at T4C1 = internal constant i32 4, !type !0
+ at T4C2 = unnamed_addr constant i32 4
+
+ at T4D1 = unnamed_addr constant i32 5, !type !0
+ at T4D2 = internal constant i32 5
+
+!0 = !{i64 0, !"typeinfo name for A"}
+!1 = !{i64 0, !"typeinfo name for B"}
+
+; CHECK: @T4A1
+; CHECK: @T4A2
+; CHECK: @T4B1
+; CHECK: @T4B2
+; CHECK: @T4C1
+; CHECK: @T4C2
+; CHECK: @T4D1
+; CHECK: @T4D2
+
+define void @test4(i32** %P1, i32** %P2, i32** %P3, i32** %P4, i32** %P5, i32** %P6, i32** %P7, i32** %P8) {
+        store i32* @T4A1, i32** %P1
+        store i32* @T4A2, i32** %P2
+        store i32* @T4B1, i32** %P3
+        store i32* @T4B2, i32** %P4
+        store i32* @T4C1, i32** %P5
+        store i32* @T4C2, i32** %P6
+        store i32* @T4D1, i32** %P7
+        store i32* @T4D2, i32** %P8
+        ret void
+}
Index: lib/Transforms/IPO/ConstantMerge.cpp
===================================================================
--- lib/Transforms/IPO/ConstantMerge.cpp
+++ lib/Transforms/IPO/ConstantMerge.cpp
@@ -60,6 +60,12 @@
   return A.hasGlobalUnnamedAddr();
 }
 
+static bool hasTypeAnnotations(const GlobalVariable *GV) {
+  SmallVector<MDNode *, 2> Types;
+  GV->getMetadata(LLVMContext::MD_type, Types);
+  return !Types.empty();
+}
+
 static unsigned getAlignment(GlobalVariable *GV) {
   unsigned Align = GV->getAlignment();
   if (Align)
@@ -113,6 +119,12 @@
       if (GV->isWeakForLinker())
         continue;
 
+      // Don't touch globals with !type annotations. An alternative is to assign
+      // the merged global the union of all type annotations, but that can make
+      // type tests less precise and also slower.
+      if (hasTypeAnnotations(GV))
+        continue;
+
       Constant *Init = GV->getInitializer();
 
       // Check to see if the initializer is already known.
@@ -155,6 +167,9 @@
       if (!Slot->hasGlobalUnnamedAddr() && !GV->hasGlobalUnnamedAddr())
         continue;
 
+      if (hasTypeAnnotations(GV))
+        continue;
+
       if (!GV->hasGlobalUnnamedAddr())
         Slot->setUnnamedAddr(GlobalValue::UnnamedAddr::None);
 


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