[llvm] r214785 - [SDAG] Fix a really, really terrible bug in the DAG combiner.

[Chandler Carruth]

Author: chandlerc
Date: Mon Aug  4 16:29:59 2014
New Revision: 214785

URL: http://llvm.org/viewvc/llvm-project?rev=214785&view=rev
Log:
[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.

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    llvm/trunk/test/CodeGen/X86/select.ll

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=214785&r1=214784&r2=214785&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Mon Aug  4 16:29:59 2014
@@ -11100,8 +11100,8 @@ SDValue DAGCombiner::SimplifySelect(SDLo
                                   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;

Modified: llvm/trunk/test/CodeGen/X86/select.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/select.ll?rev=214785&r1=214784&r2=214785&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/select.ll (original)
+++ llvm/trunk/test/CodeGen/X86/select.ll Mon Aug  4 16:29:59 2014
@@ -364,4 +364,40 @@ define i32 @trunc_select_miscompile(i32
   %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
+}