[llvm] [ARM] Update costs for ARM insts (PR #142843)

[via llvm-commits]

https://github.com/AZero13 created https://github.com/llvm/llvm-project/pull/142843

Things that can be encoded in an immediate should not have a cost.

>From 296c6374c0f9e328a1e56c7ea43621c399001dec Mon Sep 17 00:00:00 2001
From: Rose <gfunni234 at gmail.com>
Date: Wed, 4 Jun 2025 14:04:49 -0400
Subject: [PATCH] Update costs for ARM

Things that can be encoded in an immediate should not have a cost.
---
 .../lib/Target/ARM/ARMTargetTransformInfo.cpp | 44 +++++++++++++++----
 llvm/test/CodeGen/ARM/ssat.ll                 | 15 +++----
 2 files changed, 42 insertions(+), 17 deletions(-)

diff --git a/llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp b/llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
index 6c3a1ae7e1775..f61808d2a1cee 100644
--- a/llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
@@ -428,6 +428,13 @@ InstructionCost ARMTTIImpl::getIntImmCostInst(unsigned Opcode, unsigned Idx,
   if (Opcode == Instruction::GetElementPtr && Idx != 0)
     return 0;
 
+  if ((Opcode == Instruction::Shl || Opcode == Instruction::LShr ||
+       Opcode == Instruction::AShr) &&
+      Idx == 1) {
+    // Shifts are free (are we really going to get a shift of more than 64)?
+    return 0;
+  }
+
   if (Opcode == Instruction::And) {
     // UXTB/UXTH
     if (Imm == 255 || Imm == 65535)
@@ -437,19 +444,38 @@ InstructionCost ARMTTIImpl::getIntImmCostInst(unsigned Opcode, unsigned Idx,
                     getIntImmCost(~Imm, Ty, CostKind));
   }
 
-  if (Opcode == Instruction::Add)
+  if (Opcode == Instruction::Add || Opcode == Instruction::Sub) {
+    int64_t ImmVal = Imm.getSExtValue();
+    if (!ST->isThumb())
+      if (ARM_AM::getSOImmVal((uint32_t)ImmVal) != -1 ||
+          ARM_AM::getSOImmVal(-(uint32_t)ImmVal) != -1)
+        return 0;
+    if (ST->isThumb2())
+      if (ARM_AM::getT2SOImmVal((uint32_t)ImmVal) != -1 ||
+          ARM_AM::getT2SOImmVal(-(uint32_t)ImmVal) != -1)
+        return 0;
+    // Thumb1 doesn't have cmn, and only 8-bit immediates.
+    ImmVal = ImmVal < 0 ? -ImmVal : ImmVal;
+    if (ImmVal >= 0 && ImmVal <= 255)
+      return 0;
     // Conversion to SUB is free, and means we can use -Imm instead.
     return std::min(getIntImmCost(Imm, Ty, CostKind),
                     getIntImmCost(-Imm, Ty, CostKind));
+  }
 
-  if (Opcode == Instruction::ICmp && Imm.isNegative() &&
-      Ty->getIntegerBitWidth() == 32) {
-    int64_t NegImm = -Imm.getSExtValue();
-    if (ST->isThumb2() && NegImm < 1<<12)
-      // icmp X, #-C -> cmn X, #C
-      return 0;
-    if (ST->isThumb() && NegImm < 1<<8)
-      // icmp X, #-C -> adds X, #C
+  if (Opcode == Instruction::ICmp && Ty->getIntegerBitWidth() == 32) {
+    int64_t ImmVal = Imm.getSExtValue();
+    if (!ST->isThumb())
+      if (ARM_AM::getSOImmVal((uint32_t)ImmVal) != -1 ||
+          ARM_AM::getSOImmVal(-(uint32_t)ImmVal) != -1)
+        return 0;
+    if (ST->isThumb2())
+      if (ARM_AM::getT2SOImmVal((uint32_t)ImmVal) != -1 ||
+          ARM_AM::getT2SOImmVal(-(uint32_t)ImmVal) != -1)
+        return 0;
+    // Thumb1 doesn't have cmn, and only 8-bit immediates.
+    ImmVal = ImmVal < 0 ? -ImmVal : ImmVal;
+    if (ImmVal >= 0 && ImmVal <= 255)
       return 0;
   }
 
diff --git a/llvm/test/CodeGen/ARM/ssat.ll b/llvm/test/CodeGen/ARM/ssat.ll
index ed777f2b1882b..40058e0dcf635 100644
--- a/llvm/test/CodeGen/ARM/ssat.ll
+++ b/llvm/test/CodeGen/ARM/ssat.ll
@@ -390,12 +390,10 @@ entry:
 define i32 @no_sat_incorrect_constant(i32 %x) #0 {
 ; V4T-LABEL: no_sat_incorrect_constant:
 ; V4T:       @ %bb.0: @ %entry
-; V4T-NEXT:    mov r1, #1065353216
+; V4T-NEXT:    ldr r2, .LCPI11_0
 ; V4T-NEXT:    cmn r0, #8388608
-; V4T-NEXT:    orr r1, r1, #-1073741824
-; V4T-NEXT:    mov r2, r0
-; V4T-NEXT:    orrlt r2, r1, #1
-; V4T-NEXT:    ldr r1, .LCPI11_0
+; V4T-NEXT:    movge r2, r0
+; V4T-NEXT:    ldr r1, .LCPI11_1
 ; V4T-NEXT:    cmp r0, #8388608
 ; V4T-NEXT:    movlt r1, r2
 ; V4T-NEXT:    mov r0, r1
@@ -403,15 +401,16 @@ define i32 @no_sat_incorrect_constant(i32 %x) #0 {
 ; V4T-NEXT:    .p2align 2
 ; V4T-NEXT:  @ %bb.1:
 ; V4T-NEXT:  .LCPI11_0:
+; V4T-NEXT:    .long 4286578689 @ 0xff800001
+; V4T-NEXT:  .LCPI11_1:
 ; V4T-NEXT:    .long 8388607 @ 0x7fffff
 ;
 ; V6T2-LABEL: no_sat_incorrect_constant:
 ; V6T2:       @ %bb.0: @ %entry
-; V6T2-NEXT:    movw r2, #0
 ; V6T2-NEXT:    cmn r0, #8388608
 ; V6T2-NEXT:    mov r1, r0
-; V6T2-NEXT:    movt r2, #65408
-; V6T2-NEXT:    orrlt r1, r2, #1
+; V6T2-NEXT:    movwlt r1, #1
+; V6T2-NEXT:    movtlt r1, #65408
 ; V6T2-NEXT:    cmp r0, #8388608
 ; V6T2-NEXT:    movwge r1, #65535
 ; V6T2-NEXT:    movtge r1, #127