[llvm] r199025 - Switch-to-lookup tables: Don't require a result for the default
Hans Wennborg
hans at hanshq.net
Sat Jan 11 16:44:41 PST 2014
Author: hans
Date: Sat Jan 11 18:44:41 2014
New Revision: 199025
URL: http://llvm.org/viewvc/llvm-project?rev=199025&view=rev
Log:
Switch-to-lookup tables: Don't require a result for the default
case when the lookup table doesn't have any holes.
This means we can build a lookup table for switches like this:
switch (x) {
case 0: return 1;
case 1: return 2;
case 2: return 3;
case 3: return 4;
default: exit(1);
}
The default case doesn't yield a constant result here, but that doesn't matter,
since a default result is only necessary for filling holes in the lookup table,
and this table doesn't have any holes.
This makes us transform 505 more switches in a clang bootstrap, and shaves 164 KB
off the resulting clang binary.
Modified:
llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
llvm/trunk/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=199025&r1=199024&r2=199025&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Sat Jan 11 18:44:41 2014
@@ -3428,7 +3428,7 @@ GetCaseResults(SwitchInst *SI,
Res.push_back(std::make_pair(PHI, ConstVal));
}
- return true;
+ return Res.size() > 0;
}
namespace {
@@ -3499,12 +3499,14 @@ SwitchLookupTable::SwitchLookupTable(Mod
// If all values in the table are equal, this is that value.
SingleValue = Values.begin()->second;
+ Type *ValueType = Values.begin()->second->getType();
+
// Build up the table contents.
SmallVector<Constant*, 64> TableContents(TableSize);
for (size_t I = 0, E = Values.size(); I != E; ++I) {
ConstantInt *CaseVal = Values[I].first;
Constant *CaseRes = Values[I].second;
- assert(CaseRes->getType() == DefaultValue->getType());
+ assert(CaseRes->getType() == ValueType);
uint64_t Idx = (CaseVal->getValue() - Offset->getValue())
.getLimitedValue();
@@ -3516,6 +3518,8 @@ SwitchLookupTable::SwitchLookupTable(Mod
// Fill in any holes in the table with the default result.
if (Values.size() < TableSize) {
+ assert(DefaultValue && "Need a default value to fill the lookup table holes.");
+ assert(DefaultValue->getType() == ValueType);
for (uint64_t I = 0; I < TableSize; ++I) {
if (!TableContents[I])
TableContents[I] = DefaultValue;
@@ -3533,8 +3537,8 @@ SwitchLookupTable::SwitchLookupTable(Mod
}
// If the type is integer and the table fits in a register, build a bitmap.
- if (WouldFitInRegister(TD, TableSize, DefaultValue->getType())) {
- IntegerType *IT = cast<IntegerType>(DefaultValue->getType());
+ if (WouldFitInRegister(TD, TableSize, ValueType)) {
+ IntegerType *IT = cast<IntegerType>(ValueType);
APInt TableInt(TableSize * IT->getBitWidth(), 0);
for (uint64_t I = TableSize; I > 0; --I) {
TableInt <<= IT->getBitWidth();
@@ -3552,7 +3556,7 @@ SwitchLookupTable::SwitchLookupTable(Mod
}
// Store the table in an array.
- ArrayType *ArrayTy = ArrayType::get(DefaultValue->getType(), TableSize);
+ ArrayType *ArrayTy = ArrayType::get(ValueType, TableSize);
Constant *Initializer = ConstantArray::get(ArrayTy, TableContents);
Array = new GlobalVariable(M, ArrayTy, /*constant=*/ true,
@@ -3723,20 +3727,29 @@ static bool SwitchToLookupTable(SwitchIn
}
}
- // Get the resulting values for the default case.
+ // Keep track of the result types.
+ for (size_t I = 0, E = PHIs.size(); I != E; ++I) {
+ PHINode *PHI = PHIs[I];
+ ResultTypes[PHI] = ResultLists[PHI][0].second->getType();
+ }
+
+ uint64_t NumResults = ResultLists[PHIs[0]].size();
+ APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
+ uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
+ bool TableHasHoles = (NumResults < TableSize);
+
+ // If the table has holes, we need a constant result for the default case.
SmallVector<std::pair<PHINode*, Constant*>, 4> DefaultResultsList;
- if (!GetCaseResults(SI, 0, SI->getDefaultDest(), &CommonDest,
- DefaultResultsList, TD))
+ if (TableHasHoles && !GetCaseResults(SI, 0, SI->getDefaultDest(), &CommonDest,
+ DefaultResultsList, TD))
return false;
+
for (size_t I = 0, E = DefaultResultsList.size(); I != E; ++I) {
PHINode *PHI = DefaultResultsList[I].first;
Constant *Result = DefaultResultsList[I].second;
DefaultResults[PHI] = Result;
- ResultTypes[PHI] = Result->getType();
}
- APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
- uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
if (!ShouldBuildLookupTable(SI, TableSize, TTI, TD, ResultTypes))
return false;
@@ -3755,7 +3768,7 @@ static bool SwitchToLookupTable(SwitchIn
// Compute the maximum table size representable by the integer type we are
// switching upon.
unsigned CaseSize = MinCaseVal->getType()->getPrimitiveSizeInBits();
- uint64_t MaxTableSize = CaseSize > 63? UINT64_MAX : 1ULL << CaseSize;
+ uint64_t MaxTableSize = CaseSize > 63 ? UINT64_MAX : 1ULL << CaseSize;
assert(MaxTableSize >= TableSize &&
"It is impossible for a switch to have more entries than the max "
"representable value of its input integer type's size.");
Modified: llvm/trunk/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll?rev=199025&r1=199024&r2=199025&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll (original)
+++ llvm/trunk/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll Sat Jan 11 18:44:41 2014
@@ -806,3 +806,53 @@ return:
; CHECK-NOT: @switch.table
; CHECK: switch i32 %c
}
+
+; If we can build a lookup table without any holes, we don't need a default result.
+declare void @exit(i32)
+define i32 @nodefaultnoholes(i32 %c) {
+entry:
+ switch i32 %c, label %sw.default [
+ i32 0, label %return
+ i32 1, label %sw.bb1
+ i32 2, label %sw.bb2
+ i32 3, label %sw.bb3
+ ]
+
+sw.bb1: br label %return
+sw.bb2: br label %return
+sw.bb3: br label %return
+sw.default: call void @exit(i32 1)
+ unreachable
+return:
+ %x = phi i32 [ -1, %sw.bb3 ], [ 0, %sw.bb2 ], [ 123, %sw.bb1 ], [ 55, %entry ]
+ ret i32 %x
+
+; CHECK-LABEL: @nodefaultnoholes(
+; CHECK: @switch.table
+; CHECK-NOT: switch i32
+}
+
+; This lookup table will have holes, so we cannot build it without default result.
+define i32 @nodefaultwithholes(i32 %c) {
+entry:
+ switch i32 %c, label %sw.default [
+ i32 0, label %return
+ i32 1, label %sw.bb1
+ i32 2, label %sw.bb2
+ i32 3, label %sw.bb3
+ i32 5, label %sw.bb3
+ ]
+
+sw.bb1: br label %return
+sw.bb2: br label %return
+sw.bb3: br label %return
+sw.default: call void @exit(i32 1)
+ unreachable
+return:
+ %x = phi i32 [ -1, %sw.bb3 ], [ 0, %sw.bb2 ], [ 123, %sw.bb1 ], [ 55, %entry ]
+ ret i32 %x
+
+; CHECK-LABEL: @nodefaultwithholes(
+; CHECK-NOT: @switch.table
+; CHECK: switch i32
+}
More information about the llvm-commits
mailing list