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llvm-6502/test/Transforms/SampleProfile/branch.ll
Diego Novillo 0de8cecb84 Propagation of profile samples through the CFG. 
This adds a propagation heuristic to convert instruction samples
into branch weights. It implements a similar heuristic to the one
implemented by Dehao Chen on GCC.

The propagation proceeds in 3 phases:

1- Assignment of block weights. All the basic blocks in the function
   are initial assigned the same weight as their most frequently
   executed instruction.

2- Creation of equivalence classes. Since samples may be missing from
   blocks, we can fill in the gaps by setting the weights of all the
   blocks in the same equivalence class to the same weight. To compute
   the concept of equivalence, we use dominance and loop information.
   Two blocks B1 and B2 are in the same equivalence class if B1
   dominates B2, B2 post-dominates B1 and both are in the same loop.

3- Propagation of block weights into edges. This uses a simple
   propagation heuristic. The following rules are applied to every
   block B in the CFG:

   - If B has a single predecessor/successor, then the weight
     of that edge is the weight of the block.

   - If all the edges are known except one, and the weight of the
     block is already known, the weight of the unknown edge will
     be the weight of the block minus the sum of all the known
     edges. If the sum of all the known edges is larger than B's weight,
     we set the unknown edge weight to zero.

   - If there is a self-referential edge, and the weight of the block is
     known, the weight for that edge is set to the weight of the block
     minus the weight of the other incoming edges to that block (if
     known).

Since this propagation is not guaranteed to finalize for every CFG, we
only allow it to proceed for a limited number of iterations (controlled
by -sample-profile-max-propagate-iterations). It currently uses the same
GCC default of 100.

Before propagation starts, the pass builds (for each block) a list of
unique predecessors and successors. This is necessary to handle
identical edges in multiway branches. Since we visit all blocks and all
edges of the CFG, it is cleaner to build these lists once at the start
of the pass.

Finally, the patch fixes the computation of relative line locations.
The profiler emits lines relative to the function header. To discover
it, we traverse the compilation unit looking for the subprogram
corresponding to the function. The line number of that subprogram is the
line where the function begins. That becomes line zero for all the
relative locations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198972 91177308-0d34-0410-b5e6-96231b3b80d8
2014-01-10 23:23:46 +00:00

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; RUN: opt < %s -sample-profile -sample-profile-file=%S/Inputs/branch.prof | opt -analyze -branch-prob | FileCheck %s
; Original C++ code for this test case:
;
; #include <stdio.h>
; #include <stdlib.h>
;
; int main(int argc, char *argv[]) {
; if (argc < 2)
; return 1;
; double result;
; int limit = atoi(argv[1]);
; if (limit > 100) {
; double s = 23.041968;
; for (int u = 0; u < limit; u++) {
; double x = s;
; s = x + 3.049 + (double)u;
; s -= s + 3.94 / x * 0.32;
; }
; result = s;
; } else {
; result = 0;
; }
; printf("result is %lf\n", result);
; return 0;
; }
@.str = private unnamed_addr constant [15 x i8] c"result is %lf\0A\00", align 1
; Function Attrs: nounwind uwtable
define i32 @main(i32 %argc, i8** nocapture readonly %argv) #0 {
; CHECK: Printing analysis 'Branch Probability Analysis' for function 'main':
entry:
tail call void @llvm.dbg.value(metadata !{i32 %argc}, i64 0, metadata !13), !dbg !27
tail call void @llvm.dbg.value(metadata !{i8** %argv}, i64 0, metadata !14), !dbg !27
%cmp = icmp slt i32 %argc, 2, !dbg !28
br i1 %cmp, label %return, label %if.end, !dbg !28
; CHECK: edge entry -> return probability is 1 / 2 = 50%
; CHECK: edge entry -> if.end probability is 1 / 2 = 50%
if.end: ; preds = %entry
%arrayidx = getelementptr inbounds i8** %argv, i64 1, !dbg !30
%0 = load i8** %arrayidx, align 8, !dbg !30, !tbaa !31
%call = tail call i32 @atoi(i8* %0) #4, !dbg !30
tail call void @llvm.dbg.value(metadata !{i32 %call}, i64 0, metadata !17), !dbg !30
%cmp1 = icmp sgt i32 %call, 100, !dbg !35
br i1 %cmp1, label %for.body, label %if.end6, !dbg !35
; CHECK: edge if.end -> for.body probability is 1 / 2 = 50%
; CHECK: edge if.end -> if.end6 probability is 1 / 2 = 50%
for.body: ; preds = %if.end, %for.body
%u.016 = phi i32 [ %inc, %for.body ], [ 0, %if.end ]
%s.015 = phi double [ %sub, %for.body ], [ 0x40370ABE6A337A81, %if.end ]
%add = fadd double %s.015, 3.049000e+00, !dbg !36
%conv = sitofp i32 %u.016 to double, !dbg !36
%add4 = fadd double %add, %conv, !dbg !36
tail call void @llvm.dbg.value(metadata !{double %add4}, i64 0, metadata !18), !dbg !36
%div = fdiv double 3.940000e+00, %s.015, !dbg !37
%mul = fmul double %div, 3.200000e-01, !dbg !37
%add5 = fadd double %add4, %mul, !dbg !37
%sub = fsub double %add4, %add5, !dbg !37
tail call void @llvm.dbg.value(metadata !{double %sub}, i64 0, metadata !18), !dbg !37
%inc = add nsw i32 %u.016, 1, !dbg !38
tail call void @llvm.dbg.value(metadata !{i32 %inc}, i64 0, metadata !21), !dbg !38
%exitcond = icmp eq i32 %inc, %call, !dbg !38
br i1 %exitcond, label %if.end6, label %for.body, !dbg !38
; CHECK: edge for.body -> if.end6 probability is 1 / 10227 = 0.00977804
; CHECK: edge for.body -> for.body probability is 10226 / 10227 = 99.9902% [HOT edge]
if.end6: ; preds = %for.body, %if.end
%result.0 = phi double [ 0.000000e+00, %if.end ], [ %sub, %for.body ]
%call7 = tail call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([15 x i8]* @.str, i64 0, i64 0), double %result.0), !dbg !39
br label %return, !dbg !40
; CHECK: edge if.end6 -> return probability is 16 / 16 = 100% [HOT edge]
return: ; preds = %entry, %if.end6
%retval.0 = phi i32 [ 0, %if.end6 ], [ 1, %entry ]
ret i32 %retval.0, !dbg !41
}
; Function Attrs: nounwind readonly
declare i32 @atoi(i8* nocapture) #1
; Function Attrs: nounwind
declare i32 @printf(i8* nocapture readonly, ...) #2
; Function Attrs: nounwind readnone
declare void @llvm.dbg.value(metadata, i64, metadata) #3
attributes #0 = { nounwind uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { nounwind readonly "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #2 = { nounwind "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #3 = { nounwind readnone }
attributes #4 = { nounwind readonly }
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!25, !42}
!llvm.ident = !{!26}
!0 = metadata !{i32 786449, metadata !1, i32 4, metadata !"clang version 3.4 (trunk 192896) (llvm/trunk 192895)", i1 true, metadata !"", i32 0, metadata !2, metadata !2, metadata !3, metadata !2, metadata !2, metadata !""} ; [ DW_TAG_compile_unit ] [./branch.cc] [DW_LANG_C_plus_plus]
!1 = metadata !{metadata !"branch.cc", metadata !"."}
!2 = metadata !{i32 0}
!3 = metadata !{metadata !4}
!4 = metadata !{i32 786478, metadata !1, metadata !5, metadata !"main", metadata !"main", metadata !"", i32 4, metadata !6, i1 false, i1 true, i32 0, i32 0, null, i32 256, i1 true, i32 (i32, i8**)* @main, null, null, metadata !12, i32 4} ; [ DW_TAG_subprogram ] [line 4] [def] [main]
!5 = metadata !{i32 786473, metadata !1} ; [ DW_TAG_file_type ] [./branch.cc]
!6 = metadata !{i32 786453, i32 0, null, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !7, i32 0, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
!7 = metadata !{metadata !8, metadata !8, metadata !9}
!8 = metadata !{i32 786468, null, null, metadata !"int", i32 0, i64 32, i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ] [int] [line 0, size 32, align 32, offset 0, enc DW_ATE_signed]
!9 = metadata !{i32 786447, null, null, metadata !"", i32 0, i64 64, i64 64, i64 0, i32 0, metadata !10} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [from ]
!10 = metadata !{i32 786447, null, null, metadata !"", i32 0, i64 64, i64 64, i64 0, i32 0, metadata !11} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [from char]
!11 = metadata !{i32 786468, null, null, metadata !"char", i32 0, i64 8, i64 8, i64 0, i32 0, i32 6} ; [ DW_TAG_base_type ] [char] [line 0, size 8, align 8, offset 0, enc DW_ATE_signed_char]
!12 = metadata !{metadata !13, metadata !14, metadata !15, metadata !17, metadata !18, metadata !21, metadata !23}
!13 = metadata !{i32 786689, metadata !4, metadata !"argc", metadata !5, i32 16777220, metadata !8, i32 0, i32 0} ; [ DW_TAG_arg_variable ] [argc] [line 4]
!14 = metadata !{i32 786689, metadata !4, metadata !"argv", metadata !5, i32 33554436, metadata !9, i32 0, i32 0} ; [ DW_TAG_arg_variable ] [argv] [line 4]
!15 = metadata !{i32 786688, metadata !4, metadata !"result", metadata !5, i32 7, metadata !16, i32 0, i32 0} ; [ DW_TAG_auto_variable ] [result] [line 7]
!16 = metadata !{i32 786468, null, null, metadata !"double", i32 0, i64 64, i64 64, i64 0, i32 0, i32 4} ; [ DW_TAG_base_type ] [double] [line 0, size 64, align 64, offset 0, enc DW_ATE_float]
!17 = metadata !{i32 786688, metadata !4, metadata !"limit", metadata !5, i32 8, metadata !8, i32 0, i32 0} ; [ DW_TAG_auto_variable ] [limit] [line 8]
!18 = metadata !{i32 786688, metadata !19, metadata !"s", metadata !5, i32 10, metadata !16, i32 0, i32 0} ; [ DW_TAG_auto_variable ] [s] [line 10]
!19 = metadata !{i32 786443, metadata !1, metadata !20, i32 9, i32 0, i32 2} ; [ DW_TAG_lexical_block ] [./branch.cc]
!20 = metadata !{i32 786443, metadata !1, metadata !4, i32 9, i32 0, i32 1} ; [ DW_TAG_lexical_block ] [./branch.cc]
!21 = metadata !{i32 786688, metadata !22, metadata !"u", metadata !5, i32 11, metadata !8, i32 0, i32 0} ; [ DW_TAG_auto_variable ] [u] [line 11]
!22 = metadata !{i32 786443, metadata !1, metadata !19, i32 11, i32 0, i32 3} ; [ DW_TAG_lexical_block ] [./branch.cc]
!23 = metadata !{i32 786688, metadata !24, metadata !"x", metadata !5, i32 12, metadata !16, i32 0, i32 0} ; [ DW_TAG_auto_variable ] [x] [line 12]
!24 = metadata !{i32 786443, metadata !1, metadata !22, i32 11, i32 0, i32 4} ; [ DW_TAG_lexical_block ] [./branch.cc]
!25 = metadata !{i32 2, metadata !"Dwarf Version", i32 4}
!26 = metadata !{metadata !"clang version 3.4 (trunk 192896) (llvm/trunk 192895)"}
!27 = metadata !{i32 4, i32 0, metadata !4, null}
!28 = metadata !{i32 5, i32 0, metadata !29, null}
!29 = metadata !{i32 786443, metadata !1, metadata !4, i32 5, i32 0, i32 0} ; [ DW_TAG_lexical_block ] [./branch.cc]
!30 = metadata !{i32 8, i32 0, metadata !4, null} ; [ DW_TAG_imported_declaration ]
!31 = metadata !{metadata !32, metadata !32, i64 0}
!32 = metadata !{metadata !"any pointer", metadata !33, i64 0}
!33 = metadata !{metadata !"omnipotent char", metadata !34, i64 0}
!34 = metadata !{metadata !"Simple C/C++ TBAA"}
!35 = metadata !{i32 9, i32 0, metadata !20, null}
!36 = metadata !{i32 13, i32 0, metadata !24, null}
!37 = metadata !{i32 14, i32 0, metadata !24, null}
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!40 = metadata !{i32 21, i32 0, metadata !4, null}
!41 = metadata !{i32 22, i32 0, metadata !4, null}
!42 = metadata !{i32 1, metadata !"Debug Info Version", i32 1}
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