Fixes a nasty dag combiner bug that causes a bunch of tests to fail at -O0.

It's not safe to use the two value CombineTo variant to combine away a dead load.
e.g. 
v1, chain2 = load chain1, loc
v2, chain3 = load chain2, loc
v3         = add v2, c 
Now we replace use of v1 with undef, use of chain2 with chain1.
ReplaceAllUsesWith() will iterate through uses of the first load and update operands:
v1, chain2 = load chain1, loc
v2, chain3 = load chain1, loc
v3         = add v2, c 
Now the second load is the same as the first load, SelectionDAG cse will ensure
the use of second load is replaced with the first load.
v1, chain2 = load chain1, loc
v3         = add v1, c
Then v1 is replaced with undef and bad things happen.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@46099 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 30 insertions, 0 deletions

diff --git a/test/CodeGen/X86/2008-01-16-InvalidDAGCombineXform.ll b/test/CodeGen/X86/2008-01-16-InvalidDAGCombineXform.ll
new file mode 100644
index 0000000000..4feb078671
--- /dev/null
+++ b/test/CodeGen/X86/2008-01-16-InvalidDAGCombineXform.ll
@@ -0,0 +1,30 @@
+; RUN: llvm-as < %s | llc -march=x86 | not grep IMPLICIT_DEF
+
+	%struct.node_t = type { double*, %struct.node_t*, %struct.node_t**, double**, double*, i32, i32 }
+
+define void @localize_local_bb19_bb(%struct.node_t** %cur_node) {
+newFuncRoot:
+	%tmp1 = load %struct.node_t** %cur_node, align 4		; <%struct.node_t*> [#uses=1]
+	%tmp2 = getelementptr %struct.node_t* %tmp1, i32 0, i32 4		; <double**> [#uses=1]
+	%tmp3 = load double** %tmp2, align 4		; <double*> [#uses=1]
+	%tmp4 = load %struct.node_t** %cur_node, align 4		; <%struct.node_t*> [#uses=1]
+	%tmp5 = getelementptr %struct.node_t* %tmp4, i32 0, i32 4		; <double**> [#uses=1]
+	store double* %tmp3, double** %tmp5, align 4
+	%tmp6 = load %struct.node_t** %cur_node, align 4		; <%struct.node_t*> [#uses=1]
+	%tmp7 = getelementptr %struct.node_t* %tmp6, i32 0, i32 3		; <double***> [#uses=1]
+	%tmp8 = load double*** %tmp7, align 4		; <double**> [#uses=1]
+	%tmp9 = load %struct.node_t** %cur_node, align 4		; <%struct.node_t*> [#uses=1]
+	%tmp10 = getelementptr %struct.node_t* %tmp9, i32 0, i32 3		; <double***> [#uses=1]
+	store double** %tmp8, double*** %tmp10, align 4
+	%tmp11 = load %struct.node_t** %cur_node, align 4		; <%struct.node_t*> [#uses=1]
+	%tmp12 = getelementptr %struct.node_t* %tmp11, i32 0, i32 0		; <double**> [#uses=1]
+	%tmp13 = load double** %tmp12, align 4		; <double*> [#uses=1]
+	%tmp14 = load %struct.node_t** %cur_node, align 4		; <%struct.node_t*> [#uses=1]
+	%tmp15 = getelementptr %struct.node_t* %tmp14, i32 0, i32 0		; <double**> [#uses=1]
+	store double* %tmp13, double** %tmp15, align 4
+	%tmp16 = load %struct.node_t** %cur_node, align 4		; <%struct.node_t*> [#uses=1]
+	%tmp17 = getelementptr %struct.node_t* %tmp16, i32 0, i32 1		; <%struct.node_t**> [#uses=1]
+	%tmp18 = load %struct.node_t** %tmp17, align 4		; <%struct.node_t*> [#uses=1]
+	store %struct.node_t* %tmp18, %struct.node_t** %cur_node, align 4
+	ret void
+}