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avoid infinite looping when folding vector multiplies of constants (PR22698)

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We were missing a check for the following fold in DAGCombiner:

// fold (fmul (fmul x, c1), c2) -> (fmul x, (fmul c1, c2))

If 'x' is also a constant, then we shouldn't do anything. Otherwise, we could end up swapping the operands back and forth forever.

This should fix:
http://llvm.org/bugs/show_bug.cgi?id=22698

Differential Revision: http://reviews.llvm.org/D7917



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230884 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjay Patel 2015-03-01 00:09:35 +00:00
parent 7497834516
commit 821bba7fda
2 changed files with 48 additions and 5 deletions
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19
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -7453,14 +7453,23 @@ SDValue DAGCombiner::visitFMUL(SDNode *N) {
// Fold scalars or any vector constants (not just splats).
// This fold is done in general by InstCombine, but extra fmul insts
// may have been generated during lowering.
SDValue N00 = N0.getOperand(0);
SDValue N01 = N0.getOperand(1);
auto *BV1 = dyn_cast<BuildVectorSDNode>(N1);
auto *BV00 = dyn_cast<BuildVectorSDNode>(N00);
auto *BV01 = dyn_cast<BuildVectorSDNode>(N01);
if ((N1CFP && isConstOrConstSplatFP(N01)) ||
(BV1 && BV01 && BV1->isConstant() && BV01->isConstant())) {
SDLoc SL(N);
SDValue MulConsts = DAG.getNode(ISD::FMUL, SL, VT, N01, N1);
return DAG.getNode(ISD::FMUL, SL, VT, N0.getOperand(0), MulConsts);
// Check 1: Make sure that the first operand of the inner multiply is NOT
// a constant. Otherwise, we may induce infinite looping.
if (!(isConstOrConstSplatFP(N00) || (BV00 && BV00->isConstant()))) {
// Check 2: Make sure that the second operand of the inner multiply and
// the second operand of the outer multiply are constants.
if ((N1CFP && isConstOrConstSplatFP(N01)) ||
(BV1 && BV01 && BV1->isConstant() && BV01->isConstant())) {
SDLoc SL(N);
SDValue MulConsts = DAG.getNode(ISD::FMUL, SL, VT, N01, N1);
return DAG.getNode(ISD::FMUL, SL, VT, N00, MulConsts);
}
}
}

34
test/CodeGen/X86/fmul-combines.ll
View File

@ -103,6 +103,40 @@ define <4 x float> @fmul_v4f32_two_consts_no_splat_multiple_use(<4 x float> %x)
ret <4 x float> %a
}
; PR22698 - http://llvm.org/bugs/show_bug.cgi?id=22698
; Make sure that we don't infinite loop swapping constants back and forth.
define <4 x float> @PR22698_splats(<4 x float> %a) #0 {
%mul1 = fmul fast <4 x float> <float 2.0, float 2.0, float 2.0, float 2.0>, <float 3.0, float 3.0, float 3.0, float 3.0>
%mul2 = fmul fast <4 x float> <float 4.0, float 4.0, float 4.0, float 4.0>, %mul1
%mul3 = fmul fast <4 x float> %a, %mul2
ret <4 x float> %mul3
; CHECK: float 2.400000e+01
; CHECK: float 2.400000e+01
; CHECK: float 2.400000e+01
; CHECK: float 2.400000e+01
; CHECK-LABEL: PR22698_splats:
; CHECK: mulps
; CHECK: ret
}
; Same as above, but verify that non-splat vectors are handled correctly too.
define <4 x float> @PR22698_no_splats(<4 x float> %a) #0 {
%mul1 = fmul fast <4 x float> <float 1.0, float 2.0, float 3.0, float 4.0>, <float 5.0, float 6.0, float 7.0, float 8.0>
%mul2 = fmul fast <4 x float> <float 9.0, float 10.0, float 11.0, float 12.0>, %mul1
%mul3 = fmul fast <4 x float> %a, %mul2
ret <4 x float> %mul3
; CHECK: float 4.500000e+01
; CHECK: float 1.200000e+02
; CHECK: float 2.310000e+02
; CHECK: float 3.840000e+02
; CHECK-LABEL: PR22698_no_splats:
; CHECK: mulps
; CHECK: ret
}
; CHECK-LABEL: fmul_c2_c4_f32:
; CHECK-NOT: addss
; CHECK: mulss