DAGCombiner: Fold pointless truncate, bitcast, buildvector series

(2xi32) (truncate ((2xi64) bitcast (buildvector i32 a, i32 x, i32 b, i32 y)))
can be folded into a (2xi32) (buildvector i32 a, i32 b).

Such a DAG would cause uneccessary vdup instructions followed by vmovn
instructions.

We generate this code on ARM NEON for a setcc olt, 2xf64, 2xf64. For example, in
the vectorized version of the code below.

double A[N];
double B[N];

void test_double_compare_to_double() {
  int i;
  for(i=0;i<N;i++)
    A[i] = (double)(A[i] < B[i]);
}

radar://13191881

Fixes bug 15283.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175670 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 15 insertions, 0 deletions

diff --git a/test/CodeGen/ARM/neon_cmp.ll b/test/CodeGen/ARM/neon_cmp.ll
new file mode 100644
index 0000000000..046b5da228
--- /dev/null
+++ b/test/CodeGen/ARM/neon_cmp.ll
@@ -0,0 +1,15 @@
+; RUN: llc < %s -march=arm -mcpu=cortex-a9 | FileCheck %s
+; bug 15283
+; radar://13191881
+; CHECK: vfcmp
+define void @vfcmp(<2 x double>* %a, <2 x double>* %b) {
+  %wide.load = load <2 x double>* %a, align 4
+  %wide.load2 = load <2 x double>* %b, align 4
+; CHECK-NOT: vdup.32
+; CHECK-NOT: vmovn.i64
+  %v1 = fcmp olt <2 x double> %wide.load, %wide.load2
+  %v2 = zext <2 x i1> %v1 to <2 x i32>
+  %v3 = sitofp <2 x i32> %v2 to <2 x double>
+  store <2 x double> %v3, <2 x double>* %b, align 4
+  ret void
+}