[llvm-commits] [llvm-gcc-4.2] r98626 - /llvm-gcc-4.2/trunk/gcc/llvm-backend.cpp

[Duncan Sands]

Author: baldrick
Date: Tue Mar 16 06:35:32 2010
New Revision: 98626

URL: http://llvm.org/viewvc/llvm-project?rev=98626&view=rev
Log:
If a global variable is initialized by a code sequence, then do not zero
initialize it: using 'undef' makes it easier for the optimizers to sink
initialization code into the initializer for the global.  It is not clear
if this is always correct, since it relies on the code sequence not somehow
making use of the global being zero initialized.  My limited experiments
suggest that everything is fine.  This is partial progress towards getting
better code out of the testcase in PR6551.

Modified:
    llvm-gcc-4.2/trunk/gcc/llvm-backend.cpp

Modified: llvm-gcc-4.2/trunk/gcc/llvm-backend.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm-gcc-4.2/trunk/gcc/llvm-backend.cpp?rev=98626&r1=98625&r2=98626&view=diff
==============================================================================
--- llvm-gcc-4.2/trunk/gcc/llvm-backend.cpp (original)
+++ llvm-gcc-4.2/trunk/gcc/llvm-backend.cpp Tue Mar 16 06:35:32 2010
@@ -1320,10 +1320,17 @@
   // Convert the initializer over.
   Constant *Init;
   if (DECL_INITIAL(decl) == 0 || DECL_INITIAL(decl) == error_mark_node) {
-    // This global should be zero initialized.  Reconvert the type in case the
+    // This global does not have an explicit initializer.  This usually means
+    // that it should be zero initialized.  Reconvert the type in case the
     // forward def of the global and the real def differ in type (e.g. declared
     // as 'int A[]', and defined as 'int A[100]').
-    Init = Constant::getNullValue(ConvertType(TREE_TYPE(decl)));
+    if (TYPE_NEEDS_CONSTRUCTING(TREE_TYPE(decl))) {
+      // The global will be initialized by a code sequence - it does not need to
+      // be zero initialized.
+      Init = UndefValue::get(ConvertType(TREE_TYPE(decl)));
+    } else {
+      Init = Constant::getNullValue(ConvertType(TREE_TYPE(decl)));
+    }
   } else {
     assert((TREE_CONSTANT(DECL_INITIAL(decl)) || 
             TREE_CODE(DECL_INITIAL(decl)) == STRING_CST) &&