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The expression icmp eq (select (icmp eq x, 0), 1, x), 0 folds to false.

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Spotted by my super-optimizer in 186.crafty and 450.soplex.  We really
need a proper infrastructure for handling generalizations of this kind
of thing (which occur a lot), however this case is so simple that I decided
to go ahead and implement it directly.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@143214 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands
2011-10-28 19:01:20 +00:00
parent 2ec69faf26
commit 012f8547f7
2 changed files with 54 additions and 29 deletions
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36
lib/Analysis/InstructionSimplify.cpp
View File

@@ -416,19 +416,37 @@ static Value *ThreadCmpOverSelect(CmpInst::Predicate Pred, Value *LHS,
} }
assert(isa<SelectInst>(LHS) && "Not comparing with a select instruction!"); assert(isa<SelectInst>(LHS) && "Not comparing with a select instruction!");
SelectInst *SI = cast<SelectInst>(LHS); SelectInst *SI = cast<SelectInst>(LHS);
Value *Cond = SI->getCondition();
Value *TV = SI->getTrueValue();
Value *FV = SI->getFalseValue();
// Now that we have "cmp select(Cond, TV, FV), RHS", analyse it. // Now that we have "cmp select(Cond, TV, FV), RHS", analyse it.
// Does "cmp TV, RHS" simplify? // Does "cmp TV, RHS" simplify?
if (Value *TCmp = SimplifyCmpInst(Pred, SI->getTrueValue(), RHS, TD, DT, Value *TCmp = SimplifyCmpInst(Pred, TV, RHS, TD, DT, MaxRecurse);
MaxRecurse)) { if (!TCmp) {
// It does! Does "cmp FV, RHS" simplify? // It didn't simplify. However if "cmp TV, RHS" is equal to the select
if (Value *FCmp = SimplifyCmpInst(Pred, SI->getFalseValue(), RHS, TD, DT, // condition itself then we can replace it with 'true'.
MaxRecurse)) { if (match(Cond, m_ICmp(Pred, m_Specific(TV), m_Specific(RHS))))
// It does! If they simplified to the same value, then use it as the TCmp = getTrue(Cond->getType());
// result of the original comparison. }
if (!TCmp)
return 0;
// Does "cmp FV, RHS" simplify?
Value *FCmp = SimplifyCmpInst(Pred, FV, RHS, TD, DT, MaxRecurse);
if (!FCmp) {
// It didn't simplify. However if "cmp FV, RHS" is equal to the select
// condition itself then we can replace it with 'false'.
if (match(Cond, m_ICmp(Pred, m_Specific(FV), m_Specific(RHS))))
FCmp = getFalse(Cond->getType());
}
if (!FCmp)
return 0;
// If both sides simplified to the same value, then use it as the result of
// the original comparison.
if (TCmp == FCmp) if (TCmp == FCmp)
return TCmp; return TCmp;
Value *Cond = SI->getCondition();
// If the false value simplified to false, then the result of the compare // If the false value simplified to false, then the result of the compare
// is equal to "Cond && TCmp". This also catches the case when the false // is equal to "Cond && TCmp". This also catches the case when the false
// value simplified to false and the true value to true, returning "Cond". // value simplified to false and the true value to true, returning "Cond".
@@ -447,8 +465,6 @@ static Value *ThreadCmpOverSelect(CmpInst::Predicate Pred, Value *LHS,
SimplifyXorInst(Cond, Constant::getAllOnesValue(Cond->getType()), SimplifyXorInst(Cond, Constant::getAllOnesValue(Cond->getType()),
TD, DT, MaxRecurse)) TD, DT, MaxRecurse))
return V; return V;
}
}
return 0; return 0;
} }

9
test/Transforms/InstSimplify/compare.ll
View File

@@ -204,6 +204,15 @@ define i1 @select4(i1 %cond) {
; CHECK: ret i1 %cond ; CHECK: ret i1 %cond
} }
define i1 @select5(i32 %x) {
; CHECK: @select5
%c = icmp eq i32 %x, 0
%s = select i1 %c, i32 1, i32 %x
%c2 = icmp eq i32 %s, 0
ret i1 %c2
; CHECK: ret i1 false
}
define i1 @urem1(i32 %X, i32 %Y) { define i1 @urem1(i32 %X, i32 %Y) {
; CHECK: @urem1 ; CHECK: @urem1
%A = urem i32 %X, %Y %A = urem i32 %X, %Y