[MergeFunctions] Replace all uses of unnamed_addr functions.

This reduces code size for constructs like vtables or interrupt
tables that refer to functions in global initializers.

Differential Revision: https://reviews.llvm.org/D34805

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@315852 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/IPO/MergeFunctions.cpp

@@ -628,9 +628,15 @@ void MergeFunctions::filterInstsUnrelatedToPDI(
 // call sites to point to F even when within the same translation unit.
 void MergeFunctions::writeThunk(Function *F, Function *G) {
   if (!G->isInterposable() && !MergeFunctionsPDI) {
-    // Redirect direct callers of G to F. (See note on MergeFunctionsPDI
-    // above).
-    replaceDirectCallers(G, F);
+    if (G->hasGlobalUnnamedAddr()) {
+      // If G's address is not significant, replace it entirely.
+      Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType());
+      G->replaceAllUsesWith(BitcastF);
+    } else {
+      // Redirect direct callers of G to F. (See note on MergeFunctionsPDI
+      // above).
+      replaceDirectCallers(G, F);
+    }
   }
 
   // If G was internal then we may have replaced all uses of G with F. If so,

test/Transforms/MergeFunc/merge-unnamed-addr-bitcast.ll

@@ -0,0 +1,30 @@
+; RUN: opt -S -mergefunc < %s | FileCheck %s
+
+%A = type { i32 }
+%B = type { i32 }
+
+; CHECK-NOT: @b
+
+@x = constant { i32 (i32)*, i32 (i32)* }
+  { i32 (i32)* bitcast (i32 (%A)* @a to i32 (i32)*),
+    i32 (i32)* bitcast (i32 (%B)* @b to i32 (i32)*) }
+; CHECK: { i32 (i32)* bitcast (i32 (%A)* @a to i32 (i32)*), i32 (i32)* bitcast (i32 (%A)* @a to i32 (i32)*) }
+
+define internal i32 @a(%A) unnamed_addr {
+  extractvalue %A %0, 0
+  xor i32 %2, 0
+  ret i32 %3
+}
+
+define internal i32 @b(%B) unnamed_addr {
+  extractvalue %B %0, 0
+  xor i32 %2, 0
+  ret i32 %3
+}
+
+define i32 @c(i32) {
+  insertvalue %B undef, i32 %0, 0
+  call i32 @b(%B %2)
+; CHECK: call i32 bitcast (i32 (%A)* @a to i32 (%B)*)(%B %2)
+  ret i32 %3
+}

test/Transforms/MergeFunc/merge-unnamed-addr.ll

@@ -0,0 +1,18 @@
+; RUN: opt -S -mergefunc < %s | FileCheck %s
+
+; CHECK-NOT: @b
+
+@x = constant { i32 (i32)*, i32 (i32)* } { i32 (i32)* @a, i32 (i32)* @b }
+; CHECK: { i32 (i32)* @a, i32 (i32)* @a }
+
+define internal i32 @a(i32 %a) unnamed_addr {
+  %b = xor i32 %a, 0
+  %c = xor i32 %b, 0
+  ret i32 %c
+}
+
+define internal i32 @b(i32 %a) unnamed_addr {
+  %b = xor i32 %a, 0
+  %c = xor i32 %b, 0
+  ret i32 %c
+}