[CodeGen] Combine concat_vector of trunc'd scalar to scalar_to_vector.
We already do:
concat_vectors(scalar, undef) -> scalar_to_vector(scalar)
When the scalar is legal.
When it's not, but is a truncated legal scalar, we can also do:
concat_vectors(trunc(scalar), undef) -> scalar_to_vector(scalar)
Which is equivalent, since the upper lanes are undef anyway.
While there, teach the combine to look at more than 2 operands.
Differential Revision: http://reviews.llvm.org/D8883
llvm-svn: 234530
diff --git a/llvm/test/CodeGen/AArch64/concat_vector-truncate-combine.ll b/llvm/test/CodeGen/AArch64/concat_vector-truncate-combine.ll
index c510e27..ee52786 100644
--- a/llvm/test/CodeGen/AArch64/concat_vector-truncate-combine.ll
+++ b/llvm/test/CodeGen/AArch64/concat_vector-truncate-combine.ll
@@ -2,6 +2,8 @@
target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
+; Test the (concat_vectors (trunc), (trunc)) pattern.
+
define <4 x i16> @test_concat_truncate_v2i64_to_v4i16(<2 x i64> %a, <2 x i64> %b) #0 {
entry:
; CHECK-LABEL: test_concat_truncate_v2i64_to_v4i16: