[X86TTI] Make constant base pointers for getElementPtr opaque.

If getElementPtr uses a constant as base pointer, then make the constant opaque.
This prevents constant folding it with the offset. The offset can usually be
encoded in the load/store instruction itself and the base address doesn't have
to be rematerialized several times.

llvm-svn: 204739

1 files changed, 3 insertions, 2 deletions

diff --git a/llvm/lib/Target/X86/X86TargetTransformInfo.cpp b/llvm/lib/Target/X86/X86TargetTransformInfo.cpp
index 46a1e16d4f9..80f75cd6b6a 100644
--- a/llvm/lib/Target/X86/X86TargetTransformInfo.cpp
+++ b/llvm/lib/Target/X86/X86TargetTransformInfo.cpp
@@ -798,8 +798,9 @@ unsigned X86TTI::getIntImmCost(unsigned Opcode, unsigned Idx, const APInt &Imm,
   switch (Opcode) {
   default: return TCC_Free;
   case Instruction::GetElementPtr:
-    if (Idx != 0)
-      return TCC_Free;
+    if (Idx == 0)
+      return 2 * TCC_Basic;
+    return TCC_Free;
   case Instruction::Store:
     ImmIdx = 0;
     break;