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[ARM] ADD with a negative offset can become SUB for free 

So model that directly in TTI::getIntImmCost().

llvm-svn: 281044
This commit is contained in:
James Molloy 2016-09-09 13:35:36 +00:00
parent 1454e90f86
commit 57d9dfa9ac
2 changed files with 21 additions and 0 deletions
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4
llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
View File

@ -73,6 +73,10 @@ int ARMTTIImpl::getIntImmCost(unsigned Opcode, unsigned Idx, const APInt &Imm,
// Conversion to BIC is free, and means we can use ~Imm instead. // Conversion to BIC is free, and means we can use ~Imm instead.
return std::min(getIntImmCost(Imm, Ty), getIntImmCost(~Imm, Ty)); return std::min(getIntImmCost(Imm, Ty), getIntImmCost(~Imm, Ty));
if (Opcode == Instruction::Add)
// Conversion to SUB is free, and means we can use -Imm instead.
return std::min(getIntImmCost(Imm, Ty), getIntImmCost(-Imm, Ty));
if (Opcode == Instruction::ICmp && Imm.isNegative() && if (Opcode == Instruction::ICmp && Imm.isNegative() &&
Ty->getIntegerBitWidth() == 32) { Ty->getIntegerBitWidth() == 32) {
int64_t NegImm = -Imm.getSExtValue(); int64_t NegImm = -Imm.getSExtValue();

17
llvm/test/CodeGen/ARM/immcost.ll
View File

@ -71,3 +71,20 @@ true:
ret: ret:
ret void ret void
} }
; CHECK: Function: test_add_neg
; CHECK-NOT: Collect constant i32 -5
define void @test_add_neg(i1 %cond, i32 %arg, i32 %arg2) {
entry:
%a = add i32 %arg, -5
call void @g(i32 %a)
br i1 %cond, label %true, label %ret
true:
%b = add i32 %arg2, -5
call void @g(i32 %b)
br label %ret
ret:
ret void
}