Add comments and test case for [DAG] Keep the opaque constant flag when performing...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205474 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 52806235fd2c46aad4d754f9713589fcddcfb9b5..d11ce80424489bb0018e5944021f2ee6a6142757 100644 (file)
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2535,7 +2535,11 @@ SDValue SelectionDAG::getNode(unsigned Opcode, SDLoc DL, EVT VT) {
 
 SDValue SelectionDAG::getNode(unsigned Opcode, SDLoc DL,
                               EVT VT, SDValue Operand) {
-  // Constant fold unary operations with an integer constant operand.
+  // Constant fold unary operations with an integer constant operand. Even
+  // opaque constant will be folded, because the folding of unary operations
+  // doesn't create new constants with different values. Nevertheless, the
+  // opaque flag is preserved during folding to prevent future folding with
+  // other constants.
   if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Operand.getNode())) {
     const APInt &Val = C->getAPIntValue();
     switch (Opcode) {

diff --git a/test/CodeGen/X86/const-base-addr.ll b/test/CodeGen/X86/const-base-addr.ll
new file mode 100644 (file)
index 0000000..f859d7f
--- /dev/null
+++ b/test/CodeGen/X86/const-base-addr.ll
@@ -0,0 +1,24 @@
+; RUN: llc < %s | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.9.0"
+
+%T = type { i32, i32, i32, i32 }
+
+define i32 @test1() nounwind {
+; CHECK-LABEL:  test1
+; CHECK:        movabsq $123456789012345678, %rcx
+; CHECK-NEXT:   movl  4(%rcx), %eax
+; CHECK-NEXT:   addl  8(%rcx), %eax
+; CHECK-NEXT:   addl  12(%rcx), %eax
+  %addr1 = getelementptr %T* inttoptr (i64 123456789012345678 to %T*), i32 0, i32 1
+  %tmp1 = load i32* %addr1
+  %addr2 = getelementptr %T* inttoptr (i64 123456789012345678 to %T*), i32 0, i32 2
+  %tmp2 = load i32* %addr2
+  %addr3 = getelementptr %T* inttoptr (i64 123456789012345678 to %T*), i32 0, i32 3
+  %tmp3 = load i32* %addr3
+  %tmp4 = add i32 %tmp1, %tmp2
+  %tmp5 = add i32 %tmp3, %tmp4
+  ret i32 %tmp5
+}
+