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AArch64: be careful of large immediates when optimising cmps. 

llvm-svn: 243492
This commit is contained in:
Tim Northover 2015-07-28 22:42:32 +00:00
parent 0dae64a554
commit 17ae83a25f
2 changed files with 38 additions and 5 deletions
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17
llvm/lib/Target/AArch64/AArch64ConditionOptimizer.cpp
View File

@ -154,11 +154,18 @@ MachineInstr *AArch64ConditionOptimizer::findSuitableCompare(
// cmn is an alias for adds with a dead destination register.
case AArch64::ADDSWri:
case AArch64::ADDSXri:
if (MRI->use_empty(I->getOperand(0).getReg()))
return I;
DEBUG(dbgs() << "Destination of cmp is not dead, " << *I << '\n');
return nullptr;
if (!I->getOperand(2).isImm()) {
DEBUG(dbgs() << "Immediate of cmp is symbolic, " << *I << '\n');
return nullptr;
} else if (I->getOperand(2).getImm() << I->getOperand(3).getImm() >=
0xfff) {
DEBUG(dbgs() << "Immediate of cmp may be out of range, " << *I << '\n');
return nullptr;
} else if (!MRI->use_empty(I->getOperand(0).getReg())) {
DEBUG(dbgs() << "Destination of cmp is not dead, " << *I << '\n');
return nullptr;
}
return I;
// Prevent false positive case like:
// cmp w19, #0

26
llvm/test/CodeGen/AArch64/combine-comparisons-by-cse.ll
View File

@ -403,6 +403,32 @@ return: ; preds = %land.lhs.true, %con
ret i32 %retval.0
}
define void @cmp_shifted(i32 %in, i32 %lhs, i32 %rhs) {
; CHECK-LABEL: cmp_shifted:
; CHECK: cmp w0, #1
; [...]
; CHECK: cmp w0, #2, lsl #12
%tst_low = icmp sgt i32 %in, 0
br i1 %tst_low, label %true, label %false
true:
call i32 @zoo(i32 128)
ret void
false:
%tst = icmp sgt i32 %in, 8191
br i1 %tst, label %truer, label %falser
truer:
call i32 @zoo(i32 42)
ret void
falser:
call i32 @zoo(i32 1)
ret void
}
declare i32 @zoo(i32)
declare double @yoo(i32)