[PATCH] D57671: [ARM] Mark 255 and 65535 as cheap for Thumb1 "And"
Dave Green via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon Feb 4 01:16:24 PST 2019
dmgreen created this revision.
dmgreen added reviewers: samparker, efriedma, t.p.northover.
Herald added subscribers: kristof.beyls, javed.absar.
Herald added a project: LLVM.
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.
Repository:
rL LLVM
https://reviews.llvm.org/D57671
Files:
lib/Target/ARM/ARMTargetTransformInfo.cpp
test/CodeGen/Thumb/uxth.ll
Index: test/CodeGen/Thumb/uxth.ll
===================================================================
--- test/CodeGen/Thumb/uxth.ll
+++ test/CodeGen/Thumb/uxth.ll
@@ -68,24 +68,18 @@
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
Index: lib/Target/ARM/ARMTargetTransformInfo.cpp
===================================================================
--- lib/Target/ARM/ARMTargetTransformInfo.cpp
+++ lib/Target/ARM/ARMTargetTransformInfo.cpp
@@ -106,9 +106,13 @@
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.
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