[llvm] update P7 v4i8 load cost (PR #108261)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-powerpc

Author: None (RolandF77)

<details>
<summary>Changes</summary>

Update cost model to reflect codegen change to use lfiwzx from https://github.com/llvm/llvm-project/pull/104507.

---
Full diff: https://github.com/llvm/llvm-project/pull/108261.diff


2 Files Affected:

- (modified) llvm/lib/Target/PowerPC/PPCTargetTransformInfo.cpp (+10-4) 
- (modified) llvm/test/Analysis/CostModel/PowerPC/vsr_load_32_64.ll (+5-2) 


``````````diff
diff --git a/llvm/lib/Target/PowerPC/PPCTargetTransformInfo.cpp b/llvm/lib/Target/PowerPC/PPCTargetTransformInfo.cpp
index b7bdbeb535d526..df0047022a2c04 100644
--- a/llvm/lib/Target/PowerPC/PPCTargetTransformInfo.cpp
+++ b/llvm/lib/Target/PowerPC/PPCTargetTransformInfo.cpp
@@ -802,12 +802,18 @@ InstructionCost PPCTTIImpl::getMemoryOpCost(unsigned Opcode, Type *Src,
   // explicitly check this case. There are also corresponding store
   // instructions.
   unsigned MemBytes = Src->getPrimitiveSizeInBits();
-  if (ST->hasVSX() && IsAltivecType &&
-      (MemBytes == 64 || (ST->hasP8Vector() && MemBytes == 32)))
-    return 1;
+  Align AlignBytes = Alignment ? *Alignment : Align(1);
+  unsigned SrcBytes = LT.second.getStoreSize();
+  if (ST->hasVSX() && IsAltivecType) {
+    if (MemBytes == 64 || (ST->hasP8Vector() && MemBytes == 32))
+      return 1;
+    // Use lfiwax/xxspltw
+    if (Opcode == Instruction::Load && MemBytes == 32)
+      if (AlignBytes < SrcBytes || Cost > 2)
+        return 2;
+  }
 
   // Aligned loads and stores are easy.
-  unsigned SrcBytes = LT.second.getStoreSize();
   if (!SrcBytes || !Alignment || *Alignment >= SrcBytes)
     return Cost;
 
diff --git a/llvm/test/Analysis/CostModel/PowerPC/vsr_load_32_64.ll b/llvm/test/Analysis/CostModel/PowerPC/vsr_load_32_64.ll
index 54cafa0ae59f39..0e7e89c18c1cba 100644
--- a/llvm/test/Analysis/CostModel/PowerPC/vsr_load_32_64.ll
+++ b/llvm/test/Analysis/CostModel/PowerPC/vsr_load_32_64.ll
@@ -1,18 +1,21 @@
 ; RUN: opt < %s -passes="print<cost-model>" 2>&1 -disable-output -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr8 -mattr=+vsx | FileCheck %s
+; RUN: opt < %s -passes="print<cost-model>" 2>&1 -disable-output -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 -mattr=+vsx | FileCheck --check-prefix=P7 %s
 target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-f128:128:128-v128:128:128-n32:64"
 target triple = "powerpc64-unknown-linux-gnu"
 
 define i32 @loads(i32 %arg) {
   ; CHECK: cost of 1 {{.*}} load
+  ; P7: cost of 2 {{.*}} load
   load <4 x i8>, ptr undef, align 1
 
-  ; CHECK: cost of 1 {{.*}} load
+  ; CHECK, P7: cost of 1 {{.*}} load
   load <8 x i8>, ptr undef, align 1
 
   ; CHECK: cost of 1 {{.*}} load
+  ; P7: cost of 2 {{.*}} load
   load <2 x i16>, ptr undef, align 2
 
-  ; CHECK: cost of 1 {{.*}} load
+  ; CHECK, P7: cost of 1 {{.*}} load
   load <4 x i16>, ptr undef, align 2
 
   ret i32 undef

``````````

</details>


https://github.com/llvm/llvm-project/pull/108261