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[ARM] Disallow icmp with negative imm and overflow 

We allow overflowing instructions if they're decreasing and only used
by an unsigned compare. Add the extra condition that the icmp cannot
be using a negative immediate.

Differential Revision: https://reviews.llvm.org/D52102

llvm-svn: 342392
This commit is contained in:
Sam Parker 2018-09-17 13:48:25 +00:00
parent fb310c0af9
commit 76d25d7f55
2 changed files with 33 additions and 0 deletions
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11
llvm/lib/Target/ARM/ARMCodeGenPrepare.cpp
View File

@ -257,9 +257,20 @@ static bool isSafeOverflow(Instruction *I) {
return false;
auto *CI = cast<ICmpInst>(*I->user_begin());
// Don't support an icmp that deals with sign bits, including negative
// immediates
if (CI->isSigned())
return false;
if (auto *Const = dyn_cast<ConstantInt>(CI->getOperand(0)))
if (Const->isNegative())
return false;
if (auto *Const = dyn_cast<ConstantInt>(CI->getOperand(1)))
if (Const->isNegative())
return false;
bool NegImm = cast<ConstantInt>(I->getOperand(1))->isNegative();
bool IsDecreasing = ((Opc == Instruction::Sub) && !NegImm) ||
((Opc == Instruction::Add) && NegImm);

22
llvm/test/CodeGen/ARM/arm-cgp-icmps.ll
View File

@ -288,3 +288,25 @@ define i32 @icmp_i15(i15 zeroext %arg0, i15 zeroext %arg1) {
ret i32 %res
}
; CHECK-COMMON-LABEL: icmp_minus_imm
; CHECK-NODSP: subs [[SUB:r[0-9]+]],
; CHECK-NODSP: uxtb [[UXT:r[0-9]+]],
; CHECK-NODSP: cmp [[UXT]], #251
; CHECK-DSP: subs [[SUB:r[0-9]+]],
; CHECK-DSP: uxtb [[UXT:r[0-9]+]],
; CHECK-DSP: cmp [[UXT]], #251
; CHECK-DSP-IMM: ldrb [[A:r[0-9]+]],
; CHECK-DSP-IMM: movs [[MINUS_7:r[0-9]+]], #249
; CHECK-DSP-IMM: uadd8 [[RES:r[0-9]+]], [[A]], [[MINUS_7]]
; CHECK-DSP-IMM: cmp [[RES]], #251
define i32 @icmp_minus_imm(i8* %a) {
entry:
%0 = load i8, i8* %a, align 1
%add.i = add i8 %0, -7
%cmp = icmp ugt i8 %add.i, -5
%conv1 = zext i1 %cmp to i32
ret i32 %conv1
}