ARM: correct liveness flags during ARMLoadStoreOpt

When we had a sequence like:

    s1 = VLDRS [r0, 1], Q0<imp-def>
    s3 = VLDRS [r0, 2], Q0<imp-use,kill>, Q0<imp-def>
    s0 = VLDRS [r0, 0], Q0<imp-use,kill>, Q0<imp-def>
    s2 = VLDRS [r0, 4], Q0<imp-use,kill>, Q0<imp-def>

we were gathering the {s0, s1} loads below the s3 load. This is fine,
but confused the verifier since now the s3 load had Q0<imp-use> with
no definition above it.

This should mark such uses <undef> as well. The liveness structure at
the beginning and end of the block is unaffected, and the true sN
definitions should prevent any dodgy reorderings being introduced
elsewhere.

rdar://problem/15124449

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192344 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 40 insertions, 0 deletions

diff --git a/test/CodeGen/ARM/vldm-liveness.ll b/test/CodeGen/ARM/vldm-liveness.ll
new file mode 100644
index 0000000..751f447
--- /dev/null
+++ b/test/CodeGen/ARM/vldm-liveness.ll
@@ -0,0 +1,40 @@
+; RUN: llc -mtriple thumbv7-apple-ios -verify-machineinstrs -o - %s | FileCheck %s
+
+; ARM load store optimizer was dealing with a sequence like:
+;     s1 = VLDRS [r0, 1], Q0<imp-def>
+;     s3 = VLDRS [r0, 2], Q0<imp-use,kill>, Q0<imp-def>
+;     s0 = VLDRS [r0, 0], Q0<imp-use,kill>, Q0<imp-def>
+;     s2 = VLDRS [r0, 4], Q0<imp-use,kill>, Q0<imp-def>
+;
+; It decided to combine the {s0, s1} loads into a single instruction in the
+; third position. However, this leaves the instruction defining s3 with a stray
+; imp-use of Q0, which is undefined.
+;
+; The verifier catches this, so this test just makes sure that appropriate
+; liveness flags are added.
+;
+; I believe the change will be tested as long as the vldmia is not the first of
+; the loads. Earlier optimisations may perturb the output over time, but
+; fiddling the indices should be sufficient to restore the test.
+
+define arm_aapcs_vfpcc <4 x float> @foo(float* %ptr) {
+; CHECK-LABEL: foo:
+; CHECK: vldr s3, [r0, #8]
+; CHECK: vldmia r0, {s0, s1}
+; CHECK: vldr s2, [r0, #16]
+   %off0 = getelementptr float* %ptr, i32 0
+   %val0 = load float* %off0
+   %off1 = getelementptr float* %ptr, i32 1
+   %val1 = load float* %off1
+   %off4 = getelementptr float* %ptr, i32 4
+   %val4 = load float* %off4
+   %off2 = getelementptr float* %ptr, i32 2
+   %val2 = load float* %off2
+
+   %vec1 = insertelement <4 x float> undef, float %val0, i32 0
+   %vec2 = insertelement <4 x float> %vec1, float %val1, i32 1
+   %vec3 = insertelement <4 x float> %vec2, float %val4, i32 2
+   %vec4 = insertelement <4 x float> %vec3, float %val2, i32 3
+
+   ret <4 x float> %vec4
+}