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[DAGCombine] fold (X >>?,exact C1) << C2 --> X << (C2-C1)

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Instcombine also does this but many opportunities only become visible
after GEPs are lowered.

llvm-svn: 240787
This commit is contained in:
Benjamin Kramer 2015-06-26 14:51:36 +00:00
parent a17cbff2f6
commit 07e70b4fa4
2 changed files with 65 additions and 0 deletions
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16
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -4362,6 +4362,22 @@ SDValue DAGCombiner::visitSHL(SDNode *N) {
}
}
// fold (shl (sr[la] exact X, C1), C2) -> (shl X, (C2-C1)) if C1 <= C2
// fold (shl (sr[la] exact X, C1), C2) -> (sr[la] X, (C2-C1)) if C1 > C2
if (N1C && (N0.getOpcode() == ISD::SRL || N0.getOpcode() == ISD::SRA) &&
cast<BinaryWithFlagsSDNode>(N0)->Flags.hasExact()) {
if (ConstantSDNode *N0C1 = isConstOrConstSplat(N0.getOperand(1))) {
uint64_t C1 = N0C1->getZExtValue();
uint64_t C2 = N1C->getZExtValue();
SDLoc DL(N);
if (C1 <= C2)
return DAG.getNode(ISD::SHL, DL, VT, N0.getOperand(0),
DAG.getConstant(C2 - C1, DL, N1.getValueType()));
return DAG.getNode(N0.getOpcode(), DL, VT, N0.getOperand(0),
DAG.getConstant(C1 - C2, DL, N1.getValueType()));
}
}
// fold (shl (srl x, c1), c2) -> (and (shl x, (sub c2, c1), MASK) or
// (and (srl x, (sub c1, c2), MASK)
// Only fold this if the inner shift has no other uses -- if it does, folding

49
llvm/test/CodeGen/X86/shift-combine.ll
View File

@ -17,3 +17,52 @@ entry:
ret i32 %tmp5
}
define i32* @test_exact1(i32 %a, i32 %b, i32* %x) {
; CHECK-LABEL: test_exact1:
; CHECK: sarl %
%sub = sub i32 %b, %a
%shr = ashr exact i32 %sub, 3
%gep = getelementptr inbounds i32, i32* %x, i32 %shr
ret i32* %gep
}
define i32* @test_exact2(i32 %a, i32 %b, i32* %x) {
; CHECK-LABEL: test_exact2:
; CHECK: sarl %
%sub = sub i32 %b, %a
%shr = ashr exact i32 %sub, 3
%gep = getelementptr inbounds i32, i32* %x, i32 %shr
ret i32* %gep
}
define i32* @test_exact4(i32 %a, i32 %b, i32* %x) {
; CHECK-LABEL: test_exact4:
; CHECK: shrl %
%sub = sub i32 %b, %a
%shr = lshr exact i32 %sub, 3
%gep = getelementptr inbounds i32, i32* %x, i32 %shr
ret i32* %gep
}
define i32* @test_exact5(i32 %a, i32 %b, i32* %x) {
; CHECK-LABEL: test_exact5:
; CHECK: shrl %
%sub = sub i32 %b, %a
%shr = lshr exact i32 %sub, 3
%gep = getelementptr inbounds i32, i32* %x, i32 %shr
ret i32* %gep
}
define i32* @test_exact6(i32 %a, i32 %b, i32* %x) {
; CHECK-LABEL: test_exact6:
; CHECK-NOT: shrl
%sub = sub i32 %b, %a
%shr = lshr exact i32 %sub, 2
%gep = getelementptr inbounds i32, i32* %x, i32 %shr
ret i32* %gep
}