[llvm] e585b33 - [AMDGPU] PHI node cost should not be counted for the size and latency.

[via llvm-commits]

Author: alex-t
Date: 2021-06-30T16:11:17+03:00
New Revision: e585b332e42321870b2cf1eeefcd68b0717570e2

URL: https://github.com/llvm/llvm-project/commit/e585b332e42321870b2cf1eeefcd68b0717570e2
DIFF: https://github.com/llvm/llvm-project/commit/e585b332e42321870b2cf1eeefcd68b0717570e2.diff

LOG: [AMDGPU] PHI node cost should not be counted for the size and latency.

  Details: https://reviews.llvm.org/D96805 changed the GCNTTIImpl::getCFInstrCost to return 1 for the PHI nodes
  for the TTI::TCK_CodeSize and TTI::TCK_SizeAndLatency. This is incorrect because the value moves that are the
  result of the PHI lowering are inserted into the basic block predecessors - not into the block itself.
  As a result of this change LoopRotate and LoopUnroll were broken because of the incorrect Loop header and loop
  body size/cost estimation.

Reviewed By: rampitec

Differential Revision: https://reviews.llvm.org/D105104

Added: 
    

Modified: 
    llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
    llvm/test/Analysis/CostModel/AMDGPU/control-flow.ll

Removed: 
    


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diff  --git a/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp b/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
index fe138fd7bf326..67886b9681aeb 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
@@ -837,10 +837,6 @@ InstructionCost GCNTTIImpl::getCFInstrCost(unsigned Opcode,
   }
   case Instruction::Ret:
     return SCost ? 1 : 10;
-  case Instruction::PHI:
-    // TODO: 1. A prediction phi won't be eliminated?
-    //       2. Estimate data copy instructions in this case.
-    return 1;
   }
   return BaseT::getCFInstrCost(Opcode, CostKind, I);
 }

diff  --git a/llvm/test/Analysis/CostModel/AMDGPU/control-flow.ll b/llvm/test/Analysis/CostModel/AMDGPU/control-flow.ll
index ef469ccb48278..88c4956f3fc0e 100644
--- a/llvm/test/Analysis/CostModel/AMDGPU/control-flow.ll
+++ b/llvm/test/Analysis/CostModel/AMDGPU/control-flow.ll
@@ -8,7 +8,7 @@
 ; SPEED: estimated cost of 10 for instruction: ret void
 ; SIZE: estimated cost of 5 for instruction: br i1
 ; SIZE: estimated cost of 1 for instruction: br label
-; SIZE: estimated cost of 1 for instruction: %phi = phi i32 [
+; SIZE: estimated cost of 0 for instruction: %phi = phi i32 [
 ; SIZE: estimated cost of 1 for instruction: ret void
 define amdgpu_kernel void @test_br_cost(i32 addrspace(1)* %out, i32 addrspace(1)* %vaddr, i32 %b) #0 {
 bb0: