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Teach the table lookup optimization to generate range compares 

when a consequtive sequence of elements all satisfies the 
predicate.  Like the double compare case, this generates better
code than the magic constant case and generalizes to more than
32/64 element array lookups.

Here are some examples where it triggers.  From 403.gcc, most
accesses to the rtx_class array are handled, e.g.:

@rtx_class = constant [153 x i8] c"xxxxxmmmmmmmmxxxxxxxxxxxxmxxxxxxiiixxxxxxxxxxxxxxxxxxxooxooooooxxoooooox3x2c21c2222ccc122222ccccaaaaaa<<<<<<<<<<<<<<<<<<111111111111bbooxxxxxxxxxxcc2211x", align 32 ; <[153 x i8]*> [#uses=547]
   %142 = icmp eq i8 %141, 105
@rtx_class = constant [153 x i8] c"xxxxxmmmmmmmmxxxxxxxxxxxxmxxxxxxiiixxxxxxxxxxxxxxxxxxxooxooooooxxoooooox3x2c21c2222ccc122222ccccaaaaaa<<<<<<<<<<<<<<<<<<111111111111bbooxxxxxxxxxxcc2211x", align 32 ; <[153 x i8]*> [#uses=543]
	   %165 = icmp eq i8 %164, 60      

Also, most of the 59-element arrays (mode_class/rid_to_yy, etc) 
optimized before are actually range compares.  This lets 32-bit
machines optimize them.

400.perlbmk has stuff like this:

400.perlbmk: PL_regkind, even for 32-bit:
@PL_regkind = constant [62 x i8] c"\00\00\02\02\02\06\06\06\06\09\09\0B\0B\0D\0E\0E\0E\11\12\12\14\14\16\16\18\18\1A\1A\1C\1C\1E\1F !!!$$&'((((,-.///88886789:;8$", align 32 ; <[62 x i8]*> [#uses=4]
	   %811 = icmp ne i8 %810, 33 

@PL_utf8skip = constant [256 x i8] c"\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\01\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\02\03\03\03\03\03\03\03\03\03\03\03\03\03\03\03\03\04\04\04\04\04\04\04\04\05\05\05\05\06\06\07\0D", align 32 ; <[256 x i8]*> [#uses=94]
	   %12 = icmp ult i8 %10, 2
           
etc.

llvm-svn: 92426
This commit is contained in:
Chris Lattner 2010-01-02 21:50:18 +00:00
parent e199d2df80
commit b56bef45f8
2 changed files with 112 additions and 25 deletions
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108
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -6053,6 +6053,14 @@ FoldCmpLoadFromIndexedGlobal(GetElementPtrInst *GEP, GlobalVariable *GV,
// form "i != 47 & i != 87". Same state transitions as for true elements.
int FirstFalseElement = Undefined, SecondFalseElement = Undefined;
/// TrueRangeEnd/FalseRangeEnd - In conjunction with First*Element, these
/// define a state machine that triggers for ranges of values that the index
/// is true or false for. This triggers on things like "abbbbc"[i] == 'b'.
/// This is -2 when undefined, -3 when overdefined, and otherwise the last
/// index in the range (inclusive). We use -2 for undefined here because we
/// use relative comparisons and don't want 0-1 to match -1.
int TrueRangeEnd = Undefined, FalseRangeEnd = Undefined;
// MagicBitvector - This is a magic bitvector where we set a bit if the
// comparison is true for element 'i'. If there are 64 elements or less in
// the array, this will fully represent all the comparison results.
@ -6067,7 +6075,15 @@ FoldCmpLoadFromIndexedGlobal(GetElementPtrInst *GEP, GlobalVariable *GV,
Init->getOperand(i),
CompareRHS, TD);
// If the result is undef for this element, ignore it.
if (isa<UndefValue>(C)) continue;
if (isa<UndefValue>(C)) {
// Extend range state machines to cover this element in case there is an
// undef in the middle of the range.
if (TrueRangeEnd == (int)i-1)
TrueRangeEnd = i;
if (FalseRangeEnd == (int)i-1)
FalseRangeEnd = i;
continue;
}
// If we can't compute the result for any of the elements, we have to give
// up evaluating the entire conditional.
@ -6077,32 +6093,54 @@ FoldCmpLoadFromIndexedGlobal(GetElementPtrInst *GEP, GlobalVariable *GV,
// update our state machines.
bool IsTrueForElt = !cast<ConstantInt>(C)->isZero();
// State machine for single index comparison.
// State machine for single/double/range index comparison.
if (IsTrueForElt) {
// Update the TrueElement state machine.
if (FirstTrueElement == Undefined)
FirstTrueElement = i;
else if (SecondTrueElement == Undefined)
SecondTrueElement = i;
else
SecondTrueElement = Overdefined;
FirstTrueElement = TrueRangeEnd = i; // First true element.
else {
// Update double-compare state machine.
if (SecondTrueElement == Undefined)
SecondTrueElement = i;
else
SecondTrueElement = Overdefined;
// Update range state machine.
if (TrueRangeEnd == (int)i-1)
TrueRangeEnd = i;
else
TrueRangeEnd = Overdefined;
}
} else {
// Update the FalseElement state machine.
if (FirstFalseElement == Undefined)
FirstFalseElement = i;
else if (SecondFalseElement == Undefined)
SecondFalseElement = i;
else
SecondFalseElement = Overdefined;
FirstFalseElement = FalseRangeEnd = i; // First false element.
else {
// Update double-compare state machine.
if (SecondFalseElement == Undefined)
SecondFalseElement = i;
else
SecondFalseElement = Overdefined;
// Update range state machine.
if (FalseRangeEnd == (int)i-1)
FalseRangeEnd = i;
else
FalseRangeEnd = Overdefined;
}
}
// If this element is in range, update our magic bitvector.
if (i < 64 && IsTrueForElt)
MagicBitvector |= 1ULL << i;
// If all of our states become overdefined, bail out early.
if (i >= 64 && SecondTrueElement == Overdefined &&
SecondFalseElement == Overdefined)
// If all of our states become overdefined, bail out early. Since the
// predicate is expensive, only check it every 8 elements. This is only
// really useful for really huge arrays.
if ((i & 8) == 0 && i >= 64 && SecondTrueElement == Overdefined &&
SecondFalseElement == Overdefined && TrueRangeEnd == Overdefined &&
FalseRangeEnd == Overdefined)
return 0;
}
@ -6110,6 +6148,7 @@ FoldCmpLoadFromIndexedGlobal(GetElementPtrInst *GEP, GlobalVariable *GV,
// order the state machines in complexity of the generated code.
Value *Idx = GEP->getOperand(2);
// If the comparison is only true for one or two elements, emit direct
// comparisons.
if (SecondTrueElement != Overdefined) {
@ -6150,6 +6189,37 @@ FoldCmpLoadFromIndexedGlobal(GetElementPtrInst *GEP, GlobalVariable *GV,
return BinaryOperator::CreateAnd(C1, C2);
}
// If the comparison can be replaced with a range comparison for the elements
// where it is true, emit the range check.
if (TrueRangeEnd != Overdefined) {
assert(TrueRangeEnd != FirstTrueElement && "Should emit single compare");
// Generate (i-FirstTrue) <u (TrueRangeEnd-FirstTrue+1).
if (FirstTrueElement) {
Value *Offs = ConstantInt::get(Idx->getType(), -FirstTrueElement);
Idx = Builder->CreateAdd(Idx, Offs);
}
Value *End = ConstantInt::get(Idx->getType(),
TrueRangeEnd-FirstTrueElement+1);
return new ICmpInst(ICmpInst::ICMP_ULT, Idx, End);
}
// False range check.
if (FalseRangeEnd != Overdefined) {
assert(FalseRangeEnd != FirstFalseElement && "Should emit single compare");
// Generate (i-FirstFalse) >u (FalseRangeEnd-FirstFalse).
if (FirstFalseElement) {
Value *Offs = ConstantInt::get(Idx->getType(), -FirstFalseElement);
Idx = Builder->CreateAdd(Idx, Offs);
}
Value *End = ConstantInt::get(Idx->getType(),
FalseRangeEnd-FirstFalseElement);
return new ICmpInst(ICmpInst::ICMP_UGT, Idx, End);
}
// If a 32-bit or 64-bit magic bitvector captures the entire comparison state
// of this load, replace it with computation that does:
// ((magic_cst >> i) & 1) != 0
@ -6166,14 +6236,8 @@ FoldCmpLoadFromIndexedGlobal(GetElementPtrInst *GEP, GlobalVariable *GV,
return new ICmpInst(ICmpInst::ICMP_NE, V, ConstantInt::get(Ty, 0));
}
// TODO: Range check
// TODO: GEP 0, i, 4
// TODO: A[i]&4 == 0
//errs() << "XFORM: " << *GV << "\n";
//errs() << "\t" << *GEP << "\n";
//errs() << "\t " << ICI << "\n\n\n\n";
// TODO: GEP 0, i, 4
return 0;
}

29
llvm/test/Transforms/InstCombine/load-cmp.ll
View File

@ -2,7 +2,8 @@
@G16 = internal constant [10 x i16] [i16 35, i16 82, i16 69, i16 81, i16 85,
i16 73, i16 82, i16 69, i16 68, i16 0]
@GD = internal constant [3 x double] [double 1.0, double 4.0, double -20.0]
@GD = internal constant [6 x double]
[double -10.0, double 1.0, double 4.0, double 2.0, double -20.0, double -40.0]
define i1 @test1(i32 %X) {
%P = getelementptr [10 x i16]* @G16, i32 0, i32 %X
@ -25,12 +26,12 @@ define i1 @test2(i32 %X) {
}
define i1 @test3(i32 %X) {
%P = getelementptr [3 x double]* @GD, i32 0, i32 %X
%P = getelementptr [6 x double]* @GD, i32 0, i32 %X
%Q = load double* %P
%R = fcmp oeq double %Q, 1.0
ret i1 %R
; CHECK: @test3
; CHECK-NEXT: %R = icmp eq i32 %X, 0
; CHECK-NEXT: %R = icmp eq i32 %X, 1
; CHECK-NEXT: ret i1 %R
}
@ -57,3 +58,25 @@ define i1 @test5(i32 %X) {
; CHECK-NEXT: %R = or i1
; CHECK-NEXT: ret i1 %R
}
define i1 @test6(i32 %X) {
%P = getelementptr [6 x double]* @GD, i32 0, i32 %X
%Q = load double* %P
%R = fcmp ogt double %Q, 0.0
ret i1 %R
; CHECK: @test6
; CHECK-NEXT: add i32 %X, -1
; CHECK-NEXT: %R = icmp ult i32 {{.*}}, 3
; CHECK-NEXT: ret i1 %R
}
define i1 @test7(i32 %X) {
%P = getelementptr [6 x double]* @GD, i32 0, i32 %X
%Q = load double* %P
%R = fcmp olt double %Q, 0.0
ret i1 %R
; CHECK: @test7
; CHECK-NEXT: add i32 %X, -1
; CHECK-NEXT: %R = icmp ugt i32 {{.*}}, 2
; CHECK-NEXT: ret i1 %R
}