[SDAG] Fix a really, really terrible bug in the DAG combiner.

This code is completely wrong. It is also dead, as if it were to *ever*
run, it would crash. Fortunately, after my work to the combiner, it is
at least *possible* to reach the code, and llvm-stress has found a test
case. Thanks to Patrick for reporting.

It would be really good if anyone who remembers how this code works and
what it was intended to do could add some more obvious test coverage
instead of my completely contrived and reduced test case. My test case
was so brittle I left a bread crumb comment in it to help the next
person to stumble on it and not know what it was actually testing for.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214785 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index cb9e13c331da56361682650c0e9095baa4e02a00..035ce57bf0f678e6037af7075f18c6158faa5b3b 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -11100,8 +11100,8 @@ SDValue DAGCombiner::SimplifySelect(SDLoc DL, SDValue N0,
                                   SCC.getOperand(0), SCC.getOperand(1),
                                   SCC.getOperand(4));
       AddToWorklist(SETCC.getNode());
-      return DAG.getSelect(SDLoc(SCC), SCC.getValueType(),
-                           SCC.getOperand(2), SCC.getOperand(3), SETCC);
+      return DAG.getSelect(SDLoc(SCC), SCC.getValueType(), SETCC,
+                           SCC.getOperand(2), SCC.getOperand(3));
     }
 
     return SCC;

diff --git a/test/CodeGen/X86/select.ll b/test/CodeGen/X86/select.ll
index 654e8652cfcba625630ad6497192438915330553..7e6f153214155bbda8cff31791ce3591b941f90d 100644 (file)
--- a/test/CodeGen/X86/select.ll
+++ b/test/CodeGen/X86/select.ll
@@ -364,4 +364,40 @@ define i32 @trunc_select_miscompile(i32 %a, i1 zeroext %cc) {
   %tmp1 = select i1 %cc, i32 3, i32 2
   %tmp2 = shl i32 %a, %tmp1
   ret i32 %tmp2
-}
\ No newline at end of file
+}
+
+define void @test19() {
+; This is a massive reduction of an llvm-stress test case that generates
+; interesting chains feeding setcc and eventually a f32 select operation. This
+; is intended to exercise the SELECT formation in the DAG combine simplifying
+; a simplified select_cc node. If it it regresses and is no longer triggering
+; that code path, it can be deleted.
+;
+; CHECK-LABEL: @test19
+; CHECK: testb
+; CHECK: cmpl
+; CHECK: ucomiss
+
+BB:
+  br label %CF
+
+CF:
+  %Cmp10 = icmp ule i8 undef, undef
+  br i1 %Cmp10, label %CF, label %CF250
+
+CF250:
+  %E12 = extractelement <4 x i32> <i32 -1, i32 -1, i32 -1, i32 -1>, i32 2
+  %Cmp32 = icmp ugt i1 %Cmp10, false
+  br i1 %Cmp32, label %CF, label %CF242
+
+CF242:
+  %Cmp38 = icmp uge i32 %E12, undef
+  %FC = uitofp i1 %Cmp38 to float
+  %Sl59 = select i1 %Cmp32, float %FC, float undef
+  %Cmp60 = fcmp ugt float undef, undef
+  br i1 %Cmp60, label %CF242, label %CF244
+
+CF244:
+  %B122 = fadd float %Sl59, undef
+  ret void
+}