[ScopeNestedCFG] Basic Blocks are cloned when containing convergent ops

[bob80905]

Description

Basic blocks containing convergent ops are being cloned, causing there to be multiple convergent ops, more than the original source. This is bad.

Steps to Reproduce

Run opt.exe on this IR:

; RUN: %opt-exe %s -scopenested -S | FileCheck %s

declare float @dx.wave.op(float) convergent


define void @CSMain(i32 %tid, float %v) convergent {
entry:
  switch i32 %tid, label %exit [
    i32 0, label %case0
    i32 1, label %case1
  ]

case0:                                          ; switch case 0

  %w0 = call float @dx.wave.op(float %v)
  br label %case1                               ; FALLTHROUGH


case1:                                          ; switch case 1
  %a = phi float [ %w0, %case0 ],
                   [ 0.0, %entry ]

  %w1 = call float @dx.wave.op(float %v)
  %sum = fadd float %a, %w1
  br label %exit


exit:
  %r = phi float [ %sum, %case1 ],
                   [ 0.0, %entry ]
  ret void
}

Actual Behavior

The observed issue is that there are 3 calls to the abstract wave op instruction, rather than the expected 2.

This can be seen here:

; ModuleID = 'C:\temp\min.ll'

; Function Attrs: convergent
declare float @dx.wave.op(float) #0

; Function Attrs: convergent
define void @CSMain(i32 %tid, float %v) #0 {
entry:
  switch i32 %tid, label %dx.EndSwitchScope [
    i32 0, label %case0
    i32 1, label %case1.4
  ], !dx.BranchKind !0

case0:                                            ; preds = %entry
  %w0 = call float @dx.wave.op(float %v)
  br label %case1

case1:                                            ; preds = %case0
  %a = phi float [ %w0, %case0 ], [ 0.000000e+00, %entry ]
  %w1 = call float @dx.wave.op(float %v)
  %sum = fadd float %a, %w1
  br label %dx.SwitchBreak

case1.4:                                          ; preds = %entry
  %a.1 = phi float [ %w0, %case0 ], [ 0.000000e+00, %entry ]
  %w1.2 = call float @dx.wave.op(float %v)
  %sum.3 = fadd float %a.1, %w1.2
  br label %dx.SwitchBreak.5

dx.EndSwitchScope:                                ; preds = %dx.SwitchBreak.5, %dx.SwitchBreak, %entry
  br label %exit, !dx.BranchKind !1

dx.SwitchBreak:                                   ; preds = %case1
  br label %dx.EndSwitchScope, !dx.BranchKind !2

dx.SwitchBreak.5:                                 ; preds = %case1.4
  br label %dx.EndSwitchScope, !dx.BranchKind !2

exit:                                             ; preds = %dx.EndSwitchScope
  %r = phi float [ %sum, %case1 ], [ 0.000000e+00, %entry ]
  ret void
}

attributes #0 = { convergent }

!0 = !{i32 4}
!1 = !{i32 5}
!2 = !{i32 7}

Environment

• DXC version: dxcompiler.dll: 1.10(5196-98bc4c27)(1.8.0.5070) - 1.8.0.5070 (move_coop_vec_feature_to_610, 55805c7-dirty)
• Host Operating System Windows 11 Version 10.0.26200 Build 26200