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Teach dag combine to fold the following transformation more aggressively:

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(OP (trunc x), (trunc y)) -> (trunc (OP x, y))

Unfortunately this simple change causes dag combine to infinite looping. The problem is the shrink demanded ops optimization tend to canonicalize expressions in the opposite manner. That is badness. This patch disable those optimizations in dag combine but instead it is done as a late pass in sdisel.

This also exposes some deficiencies in dag combine and x86 setcc / brcond lowering. Teach them to look pass ISD::TRUNCATE in various places.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92849 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2010-01-06 19:38:29 +00:00
parent b419a5cfe9
commit d40d03e1bd
12 changed files with 335 additions and 116 deletions
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6
include/llvm/Target/TargetLowering.h
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@@ -774,10 +774,12 @@ public:
/// that want to combine
struct TargetLoweringOpt {
SelectionDAG &DAG;
bool ShrinkOps;
SDValue Old;
SDValue New;
explicit TargetLoweringOpt(SelectionDAG &InDAG) : DAG(InDAG) {}
explicit TargetLoweringOpt(SelectionDAG &InDAG, bool Shrink = false) :
DAG(InDAG), ShrinkOps(Shrink) {}
bool CombineTo(SDValue O, SDValue N) {
Old = O;
@@ -1478,7 +1480,7 @@ public:
}
/// isZExtFree - Return true if any actual instruction that defines a
/// value of type Ty1 implicit zero-extends the value to Ty2 in the result
/// value of type Ty1 implicitly zero-extends the value to Ty2 in the result
/// register. This does not necessarily include registers defined in
/// unknown ways, such as incoming arguments, or copies from unknown
/// virtual registers. Also, if isTruncateFree(Ty2, Ty1) is true, this