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Transform (A == C1 || A == C2) into (A & ~(C1 ^ C2)) == C1

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if C1 and C2 differ only with one bit.
Fixes PR14708.

llvm-svn: 171270
This commit is contained in:
Jakub Staszak 2012-12-31 00:34:55 +00:00
parent 3bc1b07a1b
commit 000956e03b
2 changed files with 23 additions and 0 deletions
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12
lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
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@ -1524,6 +1524,18 @@ Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
AddCST = ConstantExpr::getSub(AddOne(RHSCst), LHSCst);
return Builder->CreateICmpULT(Add, AddCST);
}
if (LHS->getOperand(0) == RHS->getOperand(0)) {
// if LHSCst and RHSCst differ with only one bit:
// (A == C1 || A == C2) -> (A & ~(C1 ^ C2)) == C1
APInt Xor = LHSCst->getValue() ^ RHSCst->getValue();
if (Xor.isPowerOf2()) {
Value *NegCst = Builder->getInt(~Xor);
Value *And = Builder->CreateAnd(LHS->getOperand(0), NegCst);
return Builder->CreateICmp(ICmpInst::ICMP_EQ, And, LHSCst);
}
}
break; // (X == 13 | X == 15) -> no change
case ICmpInst::ICMP_UGT: // (X == 13 | X u> 14) -> no change
case ICmpInst::ICMP_SGT: // (X == 13 | X s> 14) -> no change

11
test/Transforms/InstCombine/icmp.ll
View File

@ -694,3 +694,14 @@ define i1 @test68(i32 %x) nounwind uwtable {
%cmp = icmp sgt i32 %and, 30
ret i1 %cmp
}
; PR14708
; CHECK: @test69
; CHECK: %1 = and i32 %c, -33
; CHECK: %2 = icmp eq i32 %1, 65
define i1 @test69(i32 %c) nounwind uwtable {
%1 = icmp eq i32 %c, 97
%2 = icmp eq i32 %c, 65
%3 = or i1 %1, %2
ret i1 %3
}