[SelectionDAG] Fold more offsets into GlobalAddresses

This reapplies r258296 and r258366, and also fixes an existing bug in
SelectionDAG.cpp's isMemSrcFromString, neglecting to account for the
offset in a GlobalAddressSDNode, which is uncovered by those patches.

llvm-svn: 258482

1 files changed, 18 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/negative-offset.ll b/llvm/test/CodeGen/X86/negative-offset.ll
new file mode 100644
index 00000000000..dc1b255d020
--- /dev/null
+++ b/llvm/test/CodeGen/X86/negative-offset.ll
@@ -0,0 +1,18 @@
+; RUN: llc < %s -asm-verbose=false | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Test that a constant consisting of a global symbol with a negative offset
+; is properly folded and isel'd.
+
+; CHECK-LABEL: negative_offset:
+; CHECK: movl   $G, %eax
+; CHECK: notq   %rax
+; CHECK: addq   %rdi, %rax
+; CHECK: retq
+@G = external global [8 x i32]
+define i8* @negative_offset(i8* %a) {
+  %t = getelementptr i8, i8* %a, i64 sub (i64 -1, i64 ptrtoint ([8 x i32]* @G to i64))
+  ret i8* %t
+}