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Don't create a MIN/MAX node if the underlying compare has more than one use.

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If the compare in a select pattern has another use then it can't be removed, so we'd just
be creating repeated code if we created a min/max node.

Spotted by Matt Arsenault!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239037 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
James Molloy 2015-06-04 13:48:23 +00:00
parent 6ff6fc6055
commit cd2647f4fd
2 changed files with 16 additions and 1 deletions
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6
lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
View File

@ -2282,7 +2282,11 @@ void SelectionDAGBuilder::visitSelect(const User &I) {
while (TLI.getTypeAction(Ctx, VT) == TargetLoweringBase::TypeSplitVector)
VT = TLI.getTypeToTransformTo(Ctx, VT);
if (Opc != ISD::DELETED_NODE && TLI.isOperationLegalOrCustom(Opc, VT)) {
if (Opc != ISD::DELETED_NODE && TLI.isOperationLegalOrCustom(Opc, VT) &&
// If the underlying comparison instruction is used by any other instruction,
// the consumed instructions won't be destroyed, so it is not profitable
// to convert to a min/max.
cast<SelectInst>(&I)->getCondition()->hasOneUse()) {
OpCode = Opc;
LHSVal = getValue(LHS);
RHSVal = getValue(RHS);

11
test/CodeGen/AArch64/minmax.ll
View File

@ -94,3 +94,14 @@ define <16 x i32> @t11(<16 x i32> %a, <16 x i32> %b) {
%t2 = select <16 x i1> %t1, <16 x i32> %a, <16 x i32> %b
ret <16 x i32> %t2
}
; CHECK-LABEL: t12
; CHECK-NOT: umin
; The icmp is used by two instructions, so don't produce a umin node.
define <16 x i8> @t12(<16 x i8> %a, <16 x i8> %b) {
%t1 = icmp ugt <16 x i8> %b, %a
%t2 = select <16 x i1> %t1, <16 x i8> %a, <16 x i8> %b
%t3 = zext <16 x i1> %t1 to <16 x i8>
%t4 = add <16 x i8> %t3, %t2
ret <16 x i8> %t4
}