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InstCombine: Merge "(trunc x) == C1 & (and x, CA) == C2" into a single and+icmp.
This happens when GVN widens loads. Part of PR6627. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130405 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -769,6 +769,42 @@ Value *InstCombiner::FoldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
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return Builder->CreateICmp(LHSCC, NewOr, LHSCst);
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}
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}
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// (trunc x) == C1 & (and x, CA) == C2 -> (and CA|CMAX) == C1|C2
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// where CMAX is the all ones value for the truncated type,
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// iff the lower bits of CA are zero.
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if (LHSCC == RHSCC && ICmpInst::isEquality(LHSCC) &&
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LHS->hasOneUse() && RHS->hasOneUse()) {
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Value *V;
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ConstantInt *AndCst, *SmallCst = 0, *BigCst = 0;
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// (trunc x) == C1 & (and x, CA) == C2
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if (match(Val2, m_Trunc(m_Value(V))) &&
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match(Val, m_And(m_Specific(V), m_ConstantInt(AndCst)))) {
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SmallCst = RHSCst;
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BigCst = LHSCst;
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}
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// (and x, CA) == C2 & (trunc x) == C1
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else if (match(Val, m_Trunc(m_Value(V))) &&
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match(Val2, m_And(m_Specific(V), m_ConstantInt(AndCst)))) {
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SmallCst = LHSCst;
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BigCst = RHSCst;
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}
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if (SmallCst && BigCst) {
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unsigned BigBitSize = BigCst->getType()->getBitWidth();
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unsigned SmallBitSize = SmallCst->getType()->getBitWidth();
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// Check that the low bits are zero.
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APInt Low = APInt::getLowBitsSet(BigBitSize, SmallBitSize);
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if ((Low & AndCst->getValue()) == 0) {
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Value *NewAnd = Builder->CreateAnd(V, Low | AndCst->getValue());
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APInt N = SmallCst->getValue().zext(BigBitSize) | BigCst->getValue();
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Value *NewVal = ConstantInt::get(AndCst->getType()->getContext(), N);
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return Builder->CreateICmp(LHSCC, NewAnd, NewVal);
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}
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}
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}
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// From here on, we only handle:
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// (icmp1 A, C1) & (icmp2 A, C2) --> something simpler.
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29
test/Transforms/InstCombine/merge-icmp.ll
Normal file
29
test/Transforms/InstCombine/merge-icmp.ll
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@ -0,0 +1,29 @@
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; RUN: opt -S -instcombine < %s | FileCheck %s
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define i1 @test1(i16* %x) {
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%load = load i16* %x, align 4
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%trunc = trunc i16 %load to i8
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%cmp1 = icmp eq i8 %trunc, 127
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%and = and i16 %load, -256
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%cmp2 = icmp eq i16 %and, 17664
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%or = and i1 %cmp1, %cmp2
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ret i1 %or
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; CHECK: @test1
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; CHECK-NEXT: load i16
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; CHECK-NEXT: icmp eq i16 %load, 17791
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; CHECK-NEXT: ret i1
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}
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define i1 @test2(i16* %x) {
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%load = load i16* %x, align 4
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%and = and i16 %load, -256
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%cmp1 = icmp eq i16 %and, 32512
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%trunc = trunc i16 %load to i8
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%cmp2 = icmp eq i8 %trunc, 69
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%or = and i1 %cmp1, %cmp2
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ret i1 %or
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; CHECK: @test2
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; CHECK-NEXT: load i16
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; CHECK-NEXT: icmp eq i16 %load, 32581
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; CHECK-NEXT: ret i1
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}
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