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[ARM] Mark 255 and 65535 as cheap for Thumb1 "And" 

This prevents Constant Hoisting from pulling the constant out of the block,
allowing us to still produce LDRH/UXTH nodes. LDRB/UXTB (255) is already cheap
by the default getIntImmCost, but I've added it for clarity.

Differential Revision: https://reviews.llvm.org/D57671

llvm-svn: 353040
This commit is contained in:
David Green 2019-02-04 11:58:48 +00:00
parent 75d79f472e
commit b4f36a2196
2 changed files with 17 additions and 19 deletions
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10
llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
View File

@ -106,9 +106,13 @@ int ARMTTIImpl::getIntImmCost(unsigned Opcode, unsigned Idx, const APInt &Imm,
Idx == 1)
return 0;
if (Opcode == Instruction::And)
// Conversion to BIC is free, and means we can use ~Imm instead.
return std::min(getIntImmCost(Imm, Ty), getIntImmCost(~Imm, Ty));
if (Opcode == Instruction::And) {
// UXTB/UXTH
if (Imm == 255 || Imm == 65535)
return 0;
// Conversion to BIC is free, and means we can use ~Imm instead.
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.

26
llvm/test/CodeGen/Thumb/uxth.ll
View File

@ -68,24 +68,18 @@ for.cond.cleanup:
define void @uxth_loop_2(i32* %a, i32 %n) {
; V6M-LABEL: uxth_loop_2:
; V6M: .save {r4, r5, r7, lr}
; V6M-NEXT: push {r4, r5, r7, lr}
; V6M-NEXT: movs r3, #0
; V6M-NEXT: ldr r2, .LCPI5_0
; V6M: .save {r4, lr}
; V6M-NEXT: push {r4, lr}
; V6M-NEXT: movs r2, #0
; V6M-NEXT: .LBB5_1:
; V6M-NEXT: adds r4, r3, #1
; V6M-NEXT: ands r3, r2
; V6M-NEXT: ldr r5, [r0]
; V6M-NEXT: ands r5, r2
; V6M-NEXT: muls r5, r3, r5
; V6M-NEXT: stm r0!, {r5}
; V6M-NEXT: cmp r1, r4
; V6M-NEXT: mov r3, r4
; V6M-NEXT: uxth r3, r2
; V6M-NEXT: ldrh r4, [r0]
; V6M-NEXT: muls r4, r3, r4
; V6M-NEXT: stm r0!, {r4}
; V6M-NEXT: adds r2, r2, #1
; V6M-NEXT: cmp r1, r2
; V6M-NEXT: bne .LBB5_1
; V6M-NEXT: pop {r4, r5, r7, pc}
; V6M-NEXT: .p2align 2
; V6M-NEXT: .LCPI5_0:
; V6M-NEXT: .long 65535
; V6M-NEXT: pop {r4, pc}
entry:
br label %for.body