[CostModel] Remove some negative costs.

[davemgreen]

The cost model in the past returned -1 for unknown costs, but over time this has largely been removed. This cleans up some of the uses that have remained. It uses 0/free for the cost of an insert and 1/basic for the cost of anything that is unknown.

[llvmbot]

@llvm/pr-subscribers-llvm-analysis

Author: David Green (davemgreen)

Changes

The cost model in the past returned -1 for unknown costs, but over time this has largely been removed. This cleans up some of the uses that have remained. It uses 0/free for the cost of an insert and 1/basic for the cost of anything that is unknown.

---

Full diff: https://github.com/llvm/llvm-project/pull/135533.diff

2 Files Affected:

• (modified) llvm/include/llvm/Analysis/TargetTransformInfoImpl.h (+5-5)
• (modified) llvm/test/Analysis/CostModel/RISCV/shuffle-interleave.ll (+6-6)

diff --git a/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h b/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
index 3fe0a9101fdee..c9296edf5b81d 100644
--- a/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
+++ b/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
@@ -755,8 +755,9 @@ class TargetTransformInfoImplBase {
     // Note: The `insertvalue` cost here is chosen to match the default case of
     // getInstructionCost() -- as pior to adding this helper `insertvalue` was
     // not handled.
-    if (Opcode == Instruction::InsertValue)
-      return CostKind == TTI::TCK_RecipThroughput ? -1 : TTI::TCC_Basic;
+    if (Opcode == Instruction::InsertValue &&
+        CostKind != TTI::TCK_RecipThroughput)
+      return TTI::TCC_Basic;
     return TTI::TCC_Free;
   }
 
@@ -1578,9 +1579,8 @@ class TargetTransformInfoImplCRTPBase : public TargetTransformInfoImplBase {
     }
     }
 
-    // By default, just classify everything as 'basic' or -1 to represent that
-    // don't know the throughput cost.
-    return CostKind == TTI::TCK_RecipThroughput ? -1 : TTI::TCC_Basic;
+    // By default, just classify everything remaining as 'basic'.
+    return TTI::TCC_Basic;
   }
 
   bool isExpensiveToSpeculativelyExecute(const Instruction *I) {
diff --git a/llvm/test/Analysis/CostModel/RISCV/shuffle-interleave.ll b/llvm/test/Analysis/CostModel/RISCV/shuffle-interleave.ll
index 25b066bb3dcbf..27c33dca5048a 100644
--- a/llvm/test/Analysis/CostModel/RISCV/shuffle-interleave.ll
+++ b/llvm/test/Analysis/CostModel/RISCV/shuffle-interleave.ll
@@ -58,8 +58,8 @@ define {<4 x i8>, <4 x i8>} @deinterleave_2(<8 x i8> %v) {
 ; CHECK-LABEL: 'deinterleave_2'
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %v0 = shufflevector <8 x i8> %v, <8 x i8> poison, <4 x i32> <i32 0, i32 2, i32 4, i32 6>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %v1 = shufflevector <8 x i8> %v, <8 x i8> poison, <4 x i32> <i32 1, i32 3, i32 5, i32 7>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of -1 for instruction: %res0 = insertvalue { <4 x i8>, <4 x i8> } poison, <4 x i8> %v0, 0
-; CHECK-NEXT:  Cost Model: Found an estimated cost of -1 for instruction: %res1 = insertvalue { <4 x i8>, <4 x i8> } %res0, <4 x i8> %v1, 1
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %res0 = insertvalue { <4 x i8>, <4 x i8> } poison, <4 x i8> %v0, 0
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %res1 = insertvalue { <4 x i8>, <4 x i8> } %res0, <4 x i8> %v1, 1
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret { <4 x i8>, <4 x i8> } %res1
 ;
   %v0 = shufflevector <8 x i8> %v, <8 x i8> poison, <4 x i32> <i32 0, i32 2, i32 4, i32 6>
@@ -73,8 +73,8 @@ define {<4 x i32>, <4 x i32>} @deinterleave_2_m1_dest(<8 x i32> %v) {
 ; CHECK-LABEL: 'deinterleave_2_m1_dest'
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 8 for instruction: %v0 = shufflevector <8 x i32> %v, <8 x i32> poison, <4 x i32> <i32 0, i32 2, i32 4, i32 6>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 8 for instruction: %v1 = shufflevector <8 x i32> %v, <8 x i32> poison, <4 x i32> <i32 1, i32 3, i32 5, i32 7>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of -1 for instruction: %res0 = insertvalue { <4 x i32>, <4 x i32> } poison, <4 x i32> %v0, 0
-; CHECK-NEXT:  Cost Model: Found an estimated cost of -1 for instruction: %res1 = insertvalue { <4 x i32>, <4 x i32> } %res0, <4 x i32> %v1, 1
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %res0 = insertvalue { <4 x i32>, <4 x i32> } poison, <4 x i32> %v0, 0
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %res1 = insertvalue { <4 x i32>, <4 x i32> } %res0, <4 x i32> %v1, 1
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret { <4 x i32>, <4 x i32> } %res1
 ;
   %v0 = shufflevector <8 x i32> %v, <8 x i32> poison, <4 x i32> <i32 0, i32 2, i32 4, i32 6>
@@ -88,8 +88,8 @@ define {<8 x i32>, <8 x i32>} @deinterleave_2_m2_dest(<16 x i32> %v) {
 ; CHECK-LABEL: 'deinterleave_2_m2_dest'
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 22 for instruction: %v0 = shufflevector <16 x i32> %v, <16 x i32> poison, <8 x i32> <i32 0, i32 2, i32 4, i32 6, i32 8, i32 10, i32 12, i32 14>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 22 for instruction: %v1 = shufflevector <16 x i32> %v, <16 x i32> poison, <8 x i32> <i32 1, i32 3, i32 5, i32 7, i32 9, i32 11, i32 13, i32 15>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of -1 for instruction: %res0 = insertvalue { <8 x i32>, <8 x i32> } poison, <8 x i32> %v0, 0
-; CHECK-NEXT:  Cost Model: Found an estimated cost of -1 for instruction: %res1 = insertvalue { <8 x i32>, <8 x i32> } %res0, <8 x i32> %v1, 1
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %res0 = insertvalue { <8 x i32>, <8 x i32> } poison, <8 x i32> %v0, 0
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %res1 = insertvalue { <8 x i32>, <8 x i32> } %res0, <8 x i32> %v1, 1
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret { <8 x i32>, <8 x i32> } %res1
 ;
   %v0 = shufflevector <16 x i32> %v, <16 x i32> poison, <8 x i32> <i32 0, i32 2, i32 4, i32 6, i32 8, i32 10, i32 12, i32 14>

[RKSimon]

Why not use InstructionCost::getInvalid() ?

[davemgreen]

Why not use InstructionCost::getInvalid() ?

An Insert I would not expect to be invalid, and for the one at the end of getInstructionCost, if it can return a valid cost for !Recip returning the same cost as a fallback sounded OK to me. An Invalid cost to me means "this cannot be codegenerated" (or maybe just "strongly don't do this" at times), not "I don't know".