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[Thumb1] Any imm8 should have cost of 1

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A simple MOVS rd, imm8 can materialize [-128, 127] in signed i8 type or
[0, 255] in unsigned i8 type on Thumb1.

Differential Revision: https://reviews.llvm.org/D52257

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@342898 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Zhaoshi Zheng 2018-09-24 16:15:23 +00:00
parent a7c2370e95
commit ab8edbddaa
2 changed files with 41 additions and 2 deletions
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4
lib/Target/ARM/ARMTargetTransformInfo.cpp
View File

@ -77,8 +77,8 @@ int ARMTTIImpl::getIntImmCost(const APInt &Imm, Type *Ty) {
return 1;
return ST->hasV6T2Ops() ? 2 : 3;
}
// Thumb1.
if (SImmVal >= 0 && SImmVal < 256)
// Thumb1, any i8 imm cost 1.
if (Bits == 8 || (SImmVal >= 0 && SImmVal < 256))
return 1;
if ((~SImmVal < 256) || ARM_AM::isThumbImmShiftedVal(ZImmVal))
return 2;

39
test/CodeGen/Thumb/consthoist-imm8-costs-1.ll Normal file
View File

@ -0,0 +1,39 @@
; RUN: llc %s -o - | FileCheck %s
target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
target triple = "thumbv6m-none-unknown-musleabi"
@a = global i8 undef, align 4
; Check that store-merging generates a single str i32 rather than strb+strb+strh,
; i.e., -1 is not moved by constant-hoisting.
; CHECK: movs [[R1:r[0-9]+]], #255
; CHECK: lsls [[R2:r[0-9]+]], [[R1]], #16
; CHECK: str [[R2]]
; CHECK: movs [[R3:r[0-9]+]], #255
; CHECK: lsls [[R4:r[0-9]+]], [[R3]], #16
; CHECK: str [[R4]]
; CHECK-NOT: strh
; CHECK-NOT: strb
define void @ham() {
bb:
br i1 undef, label %bb1, label %bb2
bb1:
store i8 0, i8* getelementptr inbounds (i8, i8* @a, i32 1), align 1
store i8 0, i8* getelementptr inbounds (i8, i8* @a, i32 0), align 4
store i8 -1, i8* getelementptr inbounds (i8, i8* @a, i32 2), align 2
store i8 0, i8* getelementptr inbounds (i8, i8* @a, i32 3), align 1
br label %bb3
bb2:
store i8 0, i8* getelementptr inbounds (i8, i8* @a, i32 9), align 1
store i8 0, i8* getelementptr inbounds (i8, i8* @a, i32 8), align 4
store i8 -1, i8* getelementptr inbounds (i8, i8* @a, i32 10), align 2
store i8 0, i8* getelementptr inbounds (i8, i8* @a, i32 11), align 1
br label %bb3
bb3:
ret void
}