[DAG] Expose NoSignedWrap, NoUnsignedWrap and Exact flags to SelectionDAG.

This patch modifies SelectionDAGBuilder to construct SDNodes with associated
NoSignedWrap, NoUnsignedWrap and Exact flags coming from IR BinaryOperator
instructions.

Added a new SDNode type called 'BinaryWithFlagsSDNode' to allow accessing
nsw/nuw/exact flags during codegen.

Patch by Marcello Maggioni.

llvm-svn: 210467

1 files changed, 20 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/2014-05-30-CombineAddNSW.ll b/llvm/test/CodeGen/X86/2014-05-30-CombineAddNSW.ll
new file mode 100644
index 00000000000..4580795880a
--- /dev/null
+++ b/llvm/test/CodeGen/X86/2014-05-30-CombineAddNSW.ll
@@ -0,0 +1,20 @@
+; RUN: llc < %s -march=x86-64 | FileCheck %s
+; CHECK: addl
+
+; The two additions are the same , but have different flags.
+; In theory this code should never be generated by the frontend, but this 
+; tries to test that two identical instructions with two different flags
+; actually generate two different nodes.
+;
+; Normally the combiner would see this condition without the flags 
+; and optimize the result of the sub into a register clear
+; (the final result would be 0). With the different flags though the combiner 
+; needs to keep the add + sub nodes, because the two nodes result as different
+; nodes and so cannot assume that the subtraction of the two nodes
+; generates 0 as result
+define i32 @foo(i32 %a, i32 %b) {
+  %1 = add i32 %a, %b
+  %2 = add nsw i32 %a, %b
+  %3 = sub i32 %1, %2
+  ret i32 %3
+}