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3919ffc012
BranchProbability now is represented by its numerator and denominator in uint32_t type. This patch changes this representation into a fixed point that is represented by the numerator in uint32_t type and a constant denominator 1<<31. This is quite similar to the representation of BlockMass in BlockFrequencyInfoImpl.h. There are several pros and cons of this change: Pros: 1. It uses only a half space of the current one. 2. Some operations are much faster like plus, subtraction, comparison, and scaling by an integer. Cons: 1. Constructing a probability using arbitrary numerator and denominator needs additional calculations. 2. It is a little less precise than before as we use a fixed denominator. For example, 1 - 1/3 may not be exactly identical to 1 / 3 (this will lead to many BranchProbability unit test failures). This should not matter when we only use it for branch probability. If we use it like a rational value for some precise calculations we may need another construct like ValueRatio. One important reason for this change is that we propose to store branch probabilities instead of edge weights in MachineBasicBlock. We also want clients to use probability instead of weight when adding successors to a MBB. The current BranchProbability has more space which may be a concern. Differential revision: http://reviews.llvm.org/D12603 llvm-svn: 248633
85 lines
3.6 KiB
LLVM
85 lines
3.6 KiB
LLVM
; RUN: opt < %s -analyze -branch-prob | FileCheck %s
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; In this test, the else clause is taken about 90% of the time. This was not
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; reflected in the probability computation because the weight is larger than
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; the branch weight cap (about 2 billion).
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;
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; CHECK: edge for.body -> if.then probability is 0x0cccba45 / 0x80000000 = 10.00%
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; CHECK: edge for.body -> if.else probability is 0x733345bb / 0x80000000 = 90.00% [HOT edge]
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@y = common global i64 0, align 8
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@x = common global i64 0, align 8
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@.str = private unnamed_addr constant [17 x i8] c"x = %lu\0Ay = %lu\0A\00", align 1
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; Function Attrs: inlinehint nounwind uwtable
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define i32 @main() #0 {
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entry:
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%retval = alloca i32, align 4
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%i = alloca i64, align 8
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store i32 0, i32* %retval
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store i64 0, i64* @y, align 8
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store i64 0, i64* @x, align 8
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call void @srand(i32 422304) #3
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store i64 0, i64* %i, align 8
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br label %for.cond
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for.cond: ; preds = %for.inc, %entry
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%0 = load i64, i64* %i, align 8
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%cmp = icmp ult i64 %0, 13000000000
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br i1 %cmp, label %for.body, label %for.end, !prof !1
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for.body: ; preds = %for.cond
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%call = call i32 @rand() #3
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%conv = sitofp i32 %call to double
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%mul = fmul double %conv, 1.000000e+02
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%div = fdiv double %mul, 0x41E0000000000000
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%cmp1 = fcmp ogt double %div, 9.000000e+01
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br i1 %cmp1, label %if.then, label %if.else, !prof !2
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if.then: ; preds = %for.body
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%1 = load i64, i64* @x, align 8
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%inc = add i64 %1, 1
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store i64 %inc, i64* @x, align 8
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br label %if.end
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if.else: ; preds = %for.body
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%2 = load i64, i64* @y, align 8
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%inc3 = add i64 %2, 1
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store i64 %inc3, i64* @y, align 8
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br label %if.end
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if.end: ; preds = %if.else, %if.then
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br label %for.inc
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for.inc: ; preds = %if.end
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%3 = load i64, i64* %i, align 8
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%inc4 = add i64 %3, 1
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store i64 %inc4, i64* %i, align 8
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br label %for.cond
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for.end: ; preds = %for.cond
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%4 = load i64, i64* @x, align 8
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%5 = load i64, i64* @y, align 8
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%call5 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([17 x i8], [17 x i8]* @.str, i32 0, i32 0), i64 %4, i64 %5)
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ret i32 0
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}
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; Function Attrs: nounwind
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declare void @srand(i32) #1
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; Function Attrs: nounwind
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declare i32 @rand() #1
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declare i32 @printf(i8*, ...) #2
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attributes #0 = { inlinehint nounwind uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
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attributes #1 = { nounwind "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
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attributes #2 = { "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
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attributes #3 = { nounwind }
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!llvm.ident = !{!0}
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!0 = !{!"clang version 3.7.0 (trunk 236218) (llvm/trunk 236235)"}
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!1 = !{!"branch_weights", i32 -1044967295, i32 1}
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!2 = !{!"branch_weights", i32 433323762, i32 -394957723}
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