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Canonicalize -1 - x to ~x.

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Instcombine does this but apparently there are situations where this pattern will escape the optimizer and / or created by isel. Here is a case that's seen in JavaScriptCore:
  %t1 = sub i32 0, %a
  %t2 = add i32 %t1, -1
The dag combiner pattern: ((c1-A)+c2) -> (c1+c2)-A
will fold it to -1 - %a.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93773 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2010-01-18 21:38:44 +00:00
parent 2d53c21eca
commit 1ad0e8b576
2 changed files with 14 additions and 0 deletions
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3
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -1176,6 +1176,9 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
if (N1C) if (N1C)
return DAG.getNode(ISD::ADD, N->getDebugLoc(), VT, N0, return DAG.getNode(ISD::ADD, N->getDebugLoc(), VT, N0,
DAG.getConstant(-N1C->getAPIntValue(), VT)); DAG.getConstant(-N1C->getAPIntValue(), VT));
// Canonicalize (sub -1, x) -> ~x, i.e. (xor x, -1)
if (N0C && N0C->isAllOnesValue())
return DAG.getNode(ISD::XOR, N->getDebugLoc(), VT, N1, N0);
// fold (A+B)-A -> B // fold (A+B)-A -> B
if (N0.getOpcode() == ISD::ADD && N0.getOperand(0) == N1) if (N0.getOpcode() == ISD::ADD && N0.getOperand(0) == N1)
return N0.getOperand(1); return N0.getOperand(1);

11
test/CodeGen/X86/xor.ll
View File

@ -131,3 +131,14 @@ bb12:
; X32: andl {{.*}}[[REG]] ; X32: andl {{.*}}[[REG]]
} }
define i32 @test8(i32 %a) nounwind {
; rdar://7553032
entry:
%t1 = sub i32 0, %a
%t2 = add i32 %t1, -1
ret i32 %t2
; X64: test8:
; X64: notl %eax
; X32: test8:
; X32: notl %eax
}