RegisterCoalescer: Cleanup empty subranges after shrinkToUses()

A call to removeEmptySubranges() is necessary after every operation that
potentially removes all segments from a subregister range; this case in
the register coalescer was missing.

llvm-svn: 241027

1 files changed, 20 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/AMDGPU/subreg-coalescer-undef-use.ll b/llvm/test/CodeGen/AMDGPU/subreg-coalescer-undef-use.ll
new file mode 100644
index 00000000000..e023a622984
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/subreg-coalescer-undef-use.ll
@@ -0,0 +1,20 @@
+; RUN: llc -march=amdgcn -mcpu=SI -o /dev/null %s
+; Don't crash when the use of an undefined value is only detected by the
+; register coalescer because it is hidden with subregister insert/extract.
+target triple="amdgcn--"
+
+define void @foobar(float %a0, float %a1, float addrspace(1)* %out) nounwind {
+entry:
+  %v0 = insertelement <4 x float> undef, float %a0, i32 0
+  br i1 undef, label %ift, label %ife
+
+ift:
+  %v1 = insertelement <4 x float> undef, float %a1, i32 0
+  br label %ife
+
+ife:
+  %val = phi <4 x float> [ %v1, %ift ], [ %v0, %entry ]
+  %v2 = extractelement <4 x float> %val, i32 1
+  store float %v2, float addrspace(1)* %out, align 4
+  ret void
+}