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Add simplification of floating point comparisons with the result

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of a select instruction, the same as already exists for integer
comparisons.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@118379 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2010-11-07 16:46:25 +00:00
parent 1ac7c9979a
commit 92826def59
2 changed files with 28 additions and 0 deletions
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20
lib/Analysis/InstructionSimplify.cpp
View File

@ -350,6 +350,26 @@ Value *llvm::SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
}
}
// If the comparison is with the result of a select instruction, check whether
// comparing with either branch of the select always yields the same value.
if (isa<SelectInst>(LHS) || isa<SelectInst>(RHS)) {
// Make sure the select is on the LHS.
if (!isa<SelectInst>(LHS)) {
std::swap(LHS, RHS);
Pred = CmpInst::getSwappedPredicate(Pred);
}
SelectInst *SI = cast<SelectInst>(LHS);
// Now that we have "fcmp select(cond, TV, FV), RHS", analyse it.
// Does "fcmp TV, RHS" simplify?
if (Value *TCmp = SimplifyFCmpInst(Pred, SI->getTrueValue(), RHS, TD))
// It does! Does "fcmp FV, RHS" simplify?
if (Value *FCmp = SimplifyFCmpInst(Pred, SI->getFalseValue(), RHS, TD))
// It does! If they simplified to the same value, then use it as the
// result of the original comparison.
if (TCmp == FCmp)
return TCmp;
}
return 0;
}

8
test/Transforms/InstCombine/select.ll
View File

@ -480,3 +480,11 @@ define i1 @test38(i1 %cond) {
; CHECK: @test38
; CHECK: ret i1 false
}
define i1 @test39(i1 %cond, double %x) {
%s = select i1 %cond, double %x, double 0x7FF0000000000000 ; RHS = +infty
%cmp = fcmp ule double %x, %s
ret i1 %cmp
; CHECK: @test39
; CHECK: ret i1 true
}