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SimplifyCFG: Omit range checks for switch lookup tables when default is unreachable

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The range check would get optimized away later, but we might as well not emit
them in the first place.

http://reviews.llvm.org/D6471

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227126 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hans Wennborg 2015-01-26 19:52:34 +00:00
parent d5c2318adc
commit 325385a37f
2 changed files with 37 additions and 7 deletions
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15
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -4182,19 +4182,20 @@ static bool SwitchToLookupTable(SwitchInst *SI,
"It is impossible for a switch to have more entries than the max "
"representable value of its input integer type's size.");
// If we have a fully covered lookup table, unconditionally branch to the
// lookup table BB. Otherwise, check if the condition value is within the case
// range. If it is so, branch to the new BB. Otherwise branch to SI's default
// destination.
// If the default destination is unreachable, or if the lookup table covers
// all values of the conditional variable, branch directly to the lookup table
// BB. Otherwise, check that the condition is within the case range.
const bool DefaultIsReachable =
!isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize);
BranchInst *RangeCheckBranch = nullptr;
const bool GeneratingCoveredLookupTable = MaxTableSize == TableSize;
if (GeneratingCoveredLookupTable) {
if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
Builder.CreateBr(LookupBB);
// We cached PHINodes in PHIs, to avoid accessing deleted PHINodes later,
// do not delete PHINodes here.
SI->getDefaultDest()->removePredecessor(SI->getParent(),
true/*DontDeleteUselessPHIs*/);
/*DontDeleteUselessPHIs=*/true);
} else {
Value *Cmp = Builder.CreateICmpULT(TableIndex, ConstantInt::get(
MinCaseVal->getType(), TableSize));

29
test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
View File

@ -781,6 +781,35 @@ return:
; CHECK: getelementptr inbounds [9 x i32]* @switch.table6, i32 0, i32 %switch.tableidx
}
define i32 @unreachable_default(i32 %x) {
entry:
switch i32 %x, label %default [
i32 0, label %bb0
i32 1, label %bb1
i32 2, label %bb2
i32 3, label %bb3
]
bb0: br label %return
bb1: br label %return
bb2: br label %return
bb3: br label %return
default: unreachable
return:
%retval = phi i32 [ 42, %bb0 ], [ 52, %bb1 ], [ 1, %bb2 ], [ 2, %bb3 ]
ret i32 %retval
; CHECK-LABEL: @unreachable_default(
; CHECK: entry:
; CHECK-NEXT: %switch.tableidx = sub i32 %x, 0
; CHECK-NOT: icmp
; CHECK-NOT: br 1i
; CHECK-NEXT: %switch.gep = getelementptr inbounds [4 x i32]* @switch.table7, i32 0, i32 %switch.tableidx
; CHECK-NEXT: %switch.load = load i32* %switch.gep
; CHECK-NEXT: ret i32 %switch.load
}
; Don't create a table with illegal type
define i96 @illegaltype(i32 %c) {
entry: