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Reapply [AArch64] Fix isLegalAddImmediate() to return true for valid negative values.

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Originally reviewed here: http://reviews.llvm.org/D17463

llvm-svn: 272023
This commit is contained in:
Geoff Berry 2016-06-07 16:48:43 +00:00
parent 19353b2150
commit 26dc05069f
2 changed files with 51 additions and 2 deletions
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7
lib/Target/AArch64/AArch64ISelLowering.cpp
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@ -7313,14 +7313,17 @@ EVT AArch64TargetLowering::getOptimalMemOpType(uint64_t Size, unsigned DstAlign,
// 12-bit optionally shifted immediates are legal for adds.
bool AArch64TargetLowering::isLegalAddImmediate(int64_t Immed) const {
// Avoid UB for INT64_MIN.
if (Immed == std::numeric_limits<int64_t>::min())
return false;
// Same encoding for add/sub, just flip the sign.
Immed = std::abs(Immed);
return ((Immed >> 12) == 0 || ((Immed & 0xfff) == 0 && Immed >> 24 == 0));
}
// Integer comparisons are implemented with ADDS/SUBS, so the range of valid
// immediates is the same as for an add or a sub.
bool AArch64TargetLowering::isLegalICmpImmediate(int64_t Immed) const {
if (Immed < 0)
Immed *= -1;
return isLegalAddImmediate(Immed);
}

46
test/CodeGen/AArch64/neg-imm.ll Normal file
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@ -0,0 +1,46 @@
; RUN: llc -mtriple=aarch64-linux-gnu -verify-machineinstrs -o - %s | FileCheck %s
; LSR used to pick a sub-optimal solution due to the target responding
; conservatively to isLegalAddImmediate for negative values.
declare void @foo(i32)
define void @test(i32 %px) {
; CHECK_LABEL: test:
; CHECK_LABEL: %entry
; CHECK: subs
; CHECK-NEXT: csel
entry:
%sub = add nsw i32 %px, -1
%cmp = icmp slt i32 %px, 1
%.sub = select i1 %cmp, i32 0, i32 %sub
br label %for.body
for.body:
; CHECK_LABEL: %for.body
; CHECK: cmp
; CHECK-NEXT: b.eq
; CHECK-LABEL: %if.then3
%x.015 = phi i32 [ %inc, %for.inc ], [ %.sub, %entry ]
%cmp2 = icmp eq i32 %x.015, %px
br i1 %cmp2, label %for.inc, label %if.then3
if.then3:
tail call void @foo(i32 %x.015)
br label %for.inc
for.inc:
; CHECK_LABEL: %for.inc
; CHECK: add
; CHECK-NEXT: cmp
; CHECK: b.le
; CHECK_LABEL: %for.cond.cleanup
%inc = add nsw i32 %x.015, 1
%cmp1 = icmp sgt i32 %x.015, %px
br i1 %cmp1, label %for.cond.cleanup.loopexit, label %for.body
for.cond.cleanup.loopexit:
br label %for.cond.cleanup
for.cond.cleanup:
ret void
}