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InstCombine: Merge "(trunc x) == C1 & (and x, CA) == C2" into a single and+icmp.

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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
This commit is contained in:
Benjamin Kramer 2011-04-28 16:58:40 +00:00
parent 7a20a37bac
commit 264ac878b2
2 changed files with 65 additions and 0 deletions
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36
lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
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@ -769,6 +769,42 @@ Value *InstCombiner::FoldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
return Builder->CreateICmp(LHSCC, NewOr, LHSCst);
}
}
// (trunc x) == C1 & (and x, CA) == C2 -> (and CA|CMAX) == C1|C2
// where CMAX is the all ones value for the truncated type,
// iff the lower bits of CA are zero.
if (LHSCC == RHSCC && ICmpInst::isEquality(LHSCC) &&
LHS->hasOneUse() && RHS->hasOneUse()) {
Value *V;
ConstantInt *AndCst, *SmallCst = 0, *BigCst = 0;
// (trunc x) == C1 & (and x, CA) == C2
if (match(Val2, m_Trunc(m_Value(V))) &&
match(Val, m_And(m_Specific(V), m_ConstantInt(AndCst)))) {
SmallCst = RHSCst;
BigCst = LHSCst;
}
// (and x, CA) == C2 & (trunc x) == C1
else if (match(Val, m_Trunc(m_Value(V))) &&
match(Val2, m_And(m_Specific(V), m_ConstantInt(AndCst)))) {
SmallCst = LHSCst;
BigCst = RHSCst;
}
if (SmallCst && BigCst) {
unsigned BigBitSize = BigCst->getType()->getBitWidth();
unsigned SmallBitSize = SmallCst->getType()->getBitWidth();
// Check that the low bits are zero.
APInt Low = APInt::getLowBitsSet(BigBitSize, SmallBitSize);
if ((Low & AndCst->getValue()) == 0) {
Value *NewAnd = Builder->CreateAnd(V, Low | AndCst->getValue());
APInt N = SmallCst->getValue().zext(BigBitSize) | BigCst->getValue();
Value *NewVal = ConstantInt::get(AndCst->getType()->getContext(), N);
return Builder->CreateICmp(LHSCC, NewAnd, NewVal);
}
}
}
// From here on, we only handle:
// (icmp1 A, C1) & (icmp2 A, C2) --> something simpler.

29
test/Transforms/InstCombine/merge-icmp.ll Normal file
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@ -0,0 +1,29 @@
; RUN: opt -S -instcombine < %s | FileCheck %s
define i1 @test1(i16* %x) {
%load = load i16* %x, align 4
%trunc = trunc i16 %load to i8
%cmp1 = icmp eq i8 %trunc, 127
%and = and i16 %load, -256
%cmp2 = icmp eq i16 %and, 17664
%or = and i1 %cmp1, %cmp2
ret i1 %or
; CHECK: @test1
; CHECK-NEXT: load i16
; CHECK-NEXT: icmp eq i16 %load, 17791
; CHECK-NEXT: ret i1
}
define i1 @test2(i16* %x) {
%load = load i16* %x, align 4
%and = and i16 %load, -256
%cmp1 = icmp eq i16 %and, 32512
%trunc = trunc i16 %load to i8
%cmp2 = icmp eq i8 %trunc, 69
%or = and i1 %cmp1, %cmp2
ret i1 %or
; CHECK: @test2
; CHECK-NEXT: load i16
; CHECK-NEXT: icmp eq i16 %load, 32581
; CHECK-NEXT: ret i1
}