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SimplifyCFG: Also transform switches that represent a range comparison but are not sorted into sub+icmp.

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This transforms another 1000 switches in gcc.c.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124826 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2011-02-03 22:51:41 +00:00
parent d931dca6e5
commit 042b27f40e
2 changed files with 58 additions and 7 deletions
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25
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -2241,14 +2241,25 @@ bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
/// integer range comparison into a sub, an icmp and a branch.
static bool TurnSwitchRangeIntoICmp(SwitchInst *SI) {
assert(SI->getNumCases() > 2 && "Degenerate switch?");
// We can do this transform if the switch consists of an ascending series
// and all cases point to the same destination.
for (unsigned I = 2, E = SI->getNumCases(); I != E; ++I)
if (SI->getSuccessor(I-1) != SI->getSuccessor(I) ||
SI->getCaseValue(I-1)->getValue()+1 != SI->getCaseValue(I)->getValue())
return false;
Constant *Offset = ConstantExpr::getNeg(SI->getCaseValue(1));
// Make sure all cases point to the same destination and gather the values.
SmallVector<ConstantInt *, 16> Cases;
Cases.push_back(SI->getCaseValue(1));
for (unsigned I = 2, E = SI->getNumCases(); I != E; ++I) {
if (SI->getSuccessor(I-1) != SI->getSuccessor(I))
return false;
Cases.push_back(SI->getCaseValue(I));
}
assert(Cases.size() == SI->getNumCases()-1 && "Not all cases gathered");
// Sort the case values, then check if they form a range we can transform.
array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
return false;
}
Constant *Offset = ConstantExpr::getNeg(Cases.back());
Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()-1);
Value *Sub = BinaryOperator::CreateAdd(SI->getCondition(), Offset, "off", SI);

40
test/Transforms/SimplifyCFG/switch-to-icmp.ll Normal file
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@ -0,0 +1,40 @@
; RUN: opt -S -simplifycfg < %s | FileCheck %s
define zeroext i1 @test1(i32 %x) nounwind readnone ssp noredzone {
entry:
switch i32 %x, label %lor.rhs [
i32 2, label %lor.end
i32 1, label %lor.end
i32 3, label %lor.end
]
lor.rhs:
br label %lor.end
lor.end:
%0 = phi i1 [ true, %entry ], [ false, %lor.rhs ], [ true, %entry ], [ true, %entry ]
ret i1 %0
; CHECK: @test1
; CHECK: %off = add i32 %x, -1
; CHECK: %switch = icmp ult i32 %off, 3
}
define zeroext i1 @test2(i32 %x) nounwind readnone ssp noredzone {
entry:
switch i32 %x, label %lor.rhs [
i32 0, label %lor.end
i32 1, label %lor.end
]
lor.rhs:
br label %lor.end
lor.end:
%0 = phi i1 [ true, %entry ], [ false, %lor.rhs ], [ true, %entry ]
ret i1 %0
; CHECK: @test2
; CHECK: %off = add i32 %x, 0
; CHECK: %switch = icmp ult i32 %off, 2
}