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[ConstantHoisting][X86] Improve the cost model for small constants with large types (i64 and above).

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This improves the X86 cost model for small constants with large types. Before
this commit we would even hoist trivial constants such as i96 2.

This is related to <rdar://problem/17070936>

llvm-svn: 210504
This commit is contained in:
Juergen Ributzka 2014-06-10 00:32:29 +00:00
parent cb40a8e503
commit 250efba0f3
3 changed files with 47 additions and 11 deletions
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43
lib/Target/X86/X86TargetTransformInfo.cpp
View File

@ -102,6 +102,8 @@ public:
unsigned getReductionCost(unsigned Opcode, Type *Ty,
bool IsPairwiseForm) const override;
unsigned getIntImmCost(int64_t) const;
unsigned getIntImmCost(const APInt &Imm, Type *Ty) const override;
unsigned getIntImmCost(unsigned Opcode, unsigned Idx, const APInt &Imm,
@ -808,6 +810,19 @@ unsigned X86TTI::getReductionCost(unsigned Opcode, Type *ValTy,
return TargetTransformInfo::getReductionCost(Opcode, ValTy, IsPairwise);
}
/// \brief Calculate the cost of materializing a 64-bit value. This helper
/// method might only calculate a fraction of a larger immediate. Therefore it
/// is valid to return a cost of ZERO.
unsigned X86TTI::getIntImmCost(int64_t Val) const {
if (Val == 0)
return TCC_Free;
if (isInt<32>(Val))
return TCC_Basic;
return 2 * TCC_Basic;
}
unsigned X86TTI::getIntImmCost(const APInt &Imm, Type *Ty) const {
assert(Ty->isIntegerTy());
@ -825,11 +840,21 @@ unsigned X86TTI::getIntImmCost(const APInt &Imm, Type *Ty) const {
if (Imm == 0)
return TCC_Free;
if (Imm.getBitWidth() <= 64 &&
(isInt<32>(Imm.getSExtValue()) || isUInt<32>(Imm.getZExtValue())))
return TCC_Basic;
else
return 2 * TCC_Basic;
// Sign-extend all constants to a multiple of 64-bit.
APInt ImmVal = Imm;
if (BitSize & 0x3f)
ImmVal = Imm.sext((BitSize + 63) & ~0x3fU);
// Split the constant into 64-bit chunks and calculate the cost for each
// chunk.
unsigned Cost = 0;
for (unsigned ShiftVal = 0; ShiftVal < BitSize; ShiftVal += 64) {
APInt Tmp = ImmVal.ashr(ShiftVal).sextOrTrunc(64);
int64_t Val = Tmp.getSExtValue();
Cost += getIntImmCost(Val);
}
// We need at least one instruction to materialze the constant.
return std::max(1U, Cost);
}
unsigned X86TTI::getIntImmCost(unsigned Opcode, unsigned Idx, const APInt &Imm,
@ -889,9 +914,11 @@ unsigned X86TTI::getIntImmCost(unsigned Opcode, unsigned Idx, const APInt &Imm,
break;
}
if ((Idx == ImmIdx) &&
Imm.getBitWidth() <= 64 && isInt<32>(Imm.getSExtValue()))
return TCC_Free;
if (Idx == ImmIdx) {
unsigned NumConstants = (BitSize + 63) / 64;
unsigned Cost = X86TTI::getIntImmCost(Imm, Ty);
return (Cost <= NumConstants * TCC_Basic) ? TCC_Free : Cost;
}
return X86TTI::getIntImmCost(Imm, Ty);
}

9
test/Transforms/ConstantHoisting/X86/large-immediate.ll
View File

@ -25,3 +25,12 @@ define i196 @test3(i196 %a) nounwind {
%2 = mul i196 %1, 2
ret i196 %2
}
; Check that we don't hoist immediates with small values.
define i96 @test4(i96 %a) nounwind {
; CHECK-LABEL: test4
; CHECK-NOT: %const = bitcast i96 2 to i96
%1 = mul i96 %a, 2
%2 = add i96 %1, 2
ret i96 %2
}

6
test/Transforms/ConstantHoisting/X86/stackmap.ll
View File

@ -6,11 +6,11 @@ target triple = "x86_64-apple-macosx10.9.0"
; Test if the 3rd argument of a stackmap is hoisted.
define i128 @test1(i128 %a) {
; CHECK-LABEL: @test1
; CHECK: %const = bitcast i128 13464618275673403322 to i128
; CHECK: %const = bitcast i128 134646182756734033220 to i128
; CHECK: tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 1, i32 24, i128 %const)
entry:
%0 = add i128 %a, 13464618275673403322
tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 1, i32 24, i128 13464618275673403322)
%0 = add i128 %a, 134646182756734033220
tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 1, i32 24, i128 134646182756734033220)
ret i128 %0
}