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

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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
This commit is contained in:
Chandler Carruth 2014-08-04 21:29:59 +00:00
parent 25c8b4774b
commit 8a74e2fc07
2 changed files with 39 additions and 3 deletions
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4
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -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;

36
test/CodeGen/X86/select.ll
View File

@ -365,3 +365,39 @@ define i32 @trunc_select_miscompile(i32 %a, i1 zeroext %cc) {
%tmp2 = shl i32 %a, %tmp1
ret i32 %tmp2
}
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
}