[llvm] [CostModel] Mark ssa_copy as free (PR #75294)

[David Green via llvm-commits]

https://github.com/davemgreen created https://github.com/llvm/llvm-project/pull/75294

These are intrinsics are only used ephemerally and be should be given a zero cost.

>From 99621ee30d6ab1ff26de1d30be39fcc3a53ba0a0 Mon Sep 17 00:00:00 2001
From: David Green <david.green at arm.com>
Date: Wed, 13 Dec 2023 07:40:05 +0000
Subject: [PATCH] [CostModel] Mark ssa_copy as free

These are intrinsics are only used ephemerally and be should be given a zero cost.
---
 llvm/include/llvm/CodeGen/BasicTTIImpl.h      |  2 ++
 .../CostModel/ARM/intrinsic-cost-kinds.ll     | 24 +++++++++----------
 2 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/llvm/include/llvm/CodeGen/BasicTTIImpl.h b/llvm/include/llvm/CodeGen/BasicTTIImpl.h
index e05ce2890a08c8..33db350a12102a 100644
--- a/llvm/include/llvm/CodeGen/BasicTTIImpl.h
+++ b/llvm/include/llvm/CodeGen/BasicTTIImpl.h
@@ -1510,6 +1510,8 @@ class BasicTTIImplBase : public TargetTransformInfoImplCRTPBase<T> {
     Intrinsic::ID IID = ICA.getID();
     if (Function::isTargetIntrinsic(IID))
       return TargetTransformInfo::TCC_Basic;
+    if (IID == Intrinsic::ssa_copy)
+      return TargetTransformInfo::TCC_Free;
 
     if (ICA.isTypeBasedOnly())
       return getTypeBasedIntrinsicInstrCost(ICA, CostKind);
diff --git a/llvm/test/Analysis/CostModel/ARM/intrinsic-cost-kinds.ll b/llvm/test/Analysis/CostModel/ARM/intrinsic-cost-kinds.ll
index 9a9193b36de029..d58f3348e41fed 100644
--- a/llvm/test/Analysis/CostModel/ARM/intrinsic-cost-kinds.ll
+++ b/llvm/test/Analysis/CostModel/ARM/intrinsic-cost-kinds.ll
@@ -341,27 +341,27 @@ define void @memcpy(ptr %a, ptr %b, i32 %c) {
 define void @ssa_copy() {
   ; CHECK: %{{.*}} = llvm.intr.ssa.copy %{{.*}} : f32
 ; THRU-LABEL: 'ssa_copy'
-; THRU-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %i = call i32 @llvm.ssa.copy.i32(i32 undef)
-; THRU-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %f = call float @llvm.ssa.copy.f32(float undef)
-; THRU-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %p = call ptr @llvm.ssa.copy.p0(ptr undef)
+; THRU-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %i = call i32 @llvm.ssa.copy.i32(i32 undef)
+; THRU-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %f = call float @llvm.ssa.copy.f32(float undef)
+; THRU-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %p = call ptr @llvm.ssa.copy.p0(ptr undef)
 ; THRU-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;
 ; LATE-LABEL: 'ssa_copy'
-; LATE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %i = call i32 @llvm.ssa.copy.i32(i32 undef)
-; LATE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %f = call float @llvm.ssa.copy.f32(float undef)
-; LATE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %p = call ptr @llvm.ssa.copy.p0(ptr undef)
+; LATE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %i = call i32 @llvm.ssa.copy.i32(i32 undef)
+; LATE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %f = call float @llvm.ssa.copy.f32(float undef)
+; LATE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %p = call ptr @llvm.ssa.copy.p0(ptr undef)
 ; LATE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: ret void
 ;
 ; SIZE-LABEL: 'ssa_copy'
-; SIZE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %i = call i32 @llvm.ssa.copy.i32(i32 undef)
-; SIZE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %f = call float @llvm.ssa.copy.f32(float undef)
-; SIZE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %p = call ptr @llvm.ssa.copy.p0(ptr undef)
+; SIZE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %i = call i32 @llvm.ssa.copy.i32(i32 undef)
+; SIZE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %f = call float @llvm.ssa.copy.f32(float undef)
+; SIZE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %p = call ptr @llvm.ssa.copy.p0(ptr undef)
 ; SIZE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: ret void
 ;
 ; SIZE_LATE-LABEL: 'ssa_copy'
-; SIZE_LATE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %i = call i32 @llvm.ssa.copy.i32(i32 undef)
-; SIZE_LATE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %f = call float @llvm.ssa.copy.f32(float undef)
-; SIZE_LATE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %p = call ptr @llvm.ssa.copy.p0(ptr undef)
+; SIZE_LATE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %i = call i32 @llvm.ssa.copy.i32(i32 undef)
+; SIZE_LATE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %f = call float @llvm.ssa.copy.f32(float undef)
+; SIZE_LATE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %p = call ptr @llvm.ssa.copy.p0(ptr undef)
 ; SIZE_LATE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: ret void
 ;
   %i = call i32 @llvm.ssa.copy.i32(i32 undef)