[DAG] Fix an assertion failure caused by an invalid cast in method 'BuildVectorSDNode::isConstantSplat'

This patch renames method 'isConstantSplat' as 'getConstantSplatValue'
(mainly for consistency reasons), and rewrites its logic to ensure
that we always perform a legal 'cast<ConstantSDNode>'.

Added test shift-combine-crash.ll to verify that DAGCombiner no longer crashes with an assertion failure in the attempt to simplify a vector shift by a vector of all undef counts.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204536 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 57 insertions, 0 deletions

diff --git a/test/CodeGen/X86/shift-combine-crash.ll b/test/CodeGen/X86/shift-combine-crash.ll
new file mode 100644
index 0000000000..a69a907d41
--- /dev/null
+++ b/test/CodeGen/X86/shift-combine-crash.ll
@@ -0,0 +1,57 @@
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -mcpu=corei7 > /dev/null
+
+; Verify that DAGCombiner doesn't crash with an assertion failure in the
+; attempt to cast a ISD::UNDEF node to a ConstantSDNode.
+
+; During type legalization, the vector shift operation in function @test1 is
+; split into two legal shifts that work on <2 x i64> elements.
+; The first shift of the legalized sequence would be a shift by all undefs.
+; DAGCombiner will then try to simplify the vector shift and check if the
+; vector of shift counts is a splat. Make sure that llc doesn't crash
+; at that stage.
+
+
+define <4 x i64> @test1(<4 x i64> %A) {
+  %shl = shl <4 x i64> %A, <i64 undef, i64 undef, i64 1, i64 2>
+  ret <4 x i64> %shl
+}
+
+; Also, verify that DAGCombiner doesn't crash when trying to combine shifts
+; with different combinations of undef elements in the vector shift count.
+
+define <4 x i64> @test2(<4 x i64> %A) {
+  %shl = shl <4 x i64> %A, <i64 2, i64 3, i64 undef, i64 undef>
+  ret <4 x i64> %shl
+}
+
+define <4 x i64> @test3(<4 x i64> %A) {
+  %shl = shl <4 x i64> %A, <i64 2, i64 undef, i64 3, i64 undef>
+  ret <4 x i64> %shl
+}
+
+define <4 x i64> @test4(<4 x i64> %A) {
+  %shl = shl <4 x i64> %A, <i64 undef, i64 2, i64 undef, i64 3>
+  ret <4 x i64> %shl
+}
+
+define <4 x i64> @test5(<4 x i64> %A) {
+  %shl = shl <4 x i64> %A, <i64 2, i64 undef, i64 undef, i64 undef>
+  ret <4 x i64> %shl
+}
+
+define <4 x i64> @test6(<4 x i64> %A) {
+  %shl = shl <4 x i64> %A, <i64 undef, i64 undef, i64 3, i64 undef>
+  ret <4 x i64> %shl
+}
+
+define <4 x i64> @test7(<4 x i64> %A) {
+  %shl = shl <4 x i64> %A, <i64 undef, i64 undef, i64 undef, i64 3>
+  ret <4 x i64> %shl
+}
+
+define <4 x i64> @test8(<4 x i64> %A) {
+  %shl = shl <4 x i64> %A, <i64 undef, i64 undef, i64 undef, i64 undef>
+  ret <4 x i64> %shl
+}
+
+