[DAG] Teach computeKnownBits and ComputeNumSignBits in SelectionDAG to look through EXTRACT_VECTOR_ELT.

Summary: Both computeKnownBits and ComputeNumSignBits can now do a simple
look-through of EXTRACT_VECTOR_ELT. It will compute the result based
on the known bits (or known sign bits) for the vector that the element
is extracted from.

Reviewers: bogner, tstellarAMD, mkuper

Subscribers: wdng, RKSimon, jyknight, llvm-commits, nhaehnle

Differential Revision: https://reviews.llvm.org/D25007

llvm-svn: 283347

1 files changed, 19 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/SPARC/vector-extract-elt.ll b/llvm/test/CodeGen/SPARC/vector-extract-elt.ll
new file mode 100644
index 00000000000..702f063bfcc
--- /dev/null
+++ b/llvm/test/CodeGen/SPARC/vector-extract-elt.ll
@@ -0,0 +1,19 @@
+; RUN: llc -march=sparc < %s | FileCheck %s
+
+
+; If computeKnownSignBits (in SelectionDAG) can do a simple
+; look-thru for extractelement then we we know that the add will yield a
+; non-negative result.
+define i1 @test1(<4 x i16>* %in) {
+; CHECK-LABEL: ! BB#0:
+; CHECK-NEXT:        retl
+; CHECK-NEXT:        sethi 0, %o0
+  %vec2 = load <4 x i16>, <4 x i16>* %in, align 1
+  %vec3 = lshr <4 x i16> %vec2, <i16 2, i16 2, i16 2, i16 2>
+  %vec4 = sext <4 x i16> %vec3 to <4 x i32>
+  %elt0 = extractelement <4 x i32> %vec4, i32 0
+  %elt1 = extractelement <4 x i32> %vec4, i32 1
+  %sum = add i32 %elt0, %elt1
+  %bool = icmp slt i32 %sum, 0
+  ret i1 %bool
+}