[DAGCombiner] Fix ReplaceExtractVectorEltOfLoadWithNarrowedLoad for BE

For little-endian, the function would convert (extract_vector_elt (load X), Y)
to X + Y*sizeof(elt).  For big-endian it would instead use
X + sizeof(vec) - Y*sizeof(elt).  The big-endian case wasn't right since
vector index order always follows memory/array order, even for big-endian.
(Note that the current handling has to be wrong for Y==0 since it would
access beyond the end of the vector.)

Original patch by Richard Sandiford.

llvm-svn: 236529

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/SystemZ/vec-extract-01.ll b/llvm/test/CodeGen/SystemZ/vec-extract-01.ll
new file mode 100644
index 00000000000..549392ffd64
--- /dev/null
+++ b/llvm/test/CodeGen/SystemZ/vec-extract-01.ll
@@ -0,0 +1,13 @@
+; Verify ReplaceExtractVectorEltOfLoadWithNarrowedLoad fixes
+;
+; RUN: llc < %s -mtriple=s390x-linux-gnu -mcpu=z13 | FileCheck %s
+
+; Test a memory copy of a v2i32 (via the constant pool).
+define void @f1(<2 x i32> *%dest) {
+; CHECK-LABEL: f1:
+; CHECK: lgrl [[REG:%r[0-5]]], {{[._A-Za-z0-9]}}
+; CHECK: stg [[REG]], 0(%r2)
+; CHECK: br %r14
+  store <2 x i32> <i32 1000000, i32 99999>, <2 x i32> *%dest
+  ret void
+}