Use fixed-point representation for BranchProbability.

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

1 files changed, 34 insertions, 34 deletions

diff --git a/llvm/test/Analysis/BranchProbabilityInfo/basic.ll b/llvm/test/Analysis/BranchProbabilityInfo/basic.ll
index 2c9c1561868..d833b8339aa 100644
--- a/llvm/test/Analysis/BranchProbabilityInfo/basic.ll
+++ b/llvm/test/Analysis/BranchProbabilityInfo/basic.ll
@@ -4,7 +4,7 @@ define i32 @test1(i32 %i, i32* %a) {
 ; CHECK: Printing analysis {{.*}} for function 'test1'
 entry:
   br label %body
-; CHECK: edge entry -> body probability is 16 / 16 = 100%
+; CHECK: edge entry -> body probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
 
 body:
   %iv = phi i32 [ 0, %entry ], [ %next, %body ]
@@ -15,8 +15,8 @@ body:
   %next = add i32 %iv, 1
   %exitcond = icmp eq i32 %next, %i
   br i1 %exitcond, label %exit, label %body
-; CHECK: edge body -> exit probability is 4 / 128
-; CHECK: edge body -> body probability is 124 / 128
+; CHECK: edge body -> exit probability is 0x04000000 / 0x80000000 = 3.12%
+; CHECK: edge body -> body probability is 0x7c000000 / 0x80000000 = 96.88% [HOT edge]
 
 exit:
   ret i32 %sum
@@ -27,16 +27,16 @@ define i32 @test2(i32 %i, i32 %a, i32 %b) {
 entry:
   %cond = icmp ult i32 %i, 42
   br i1 %cond, label %then, label %else, !prof !0
-; CHECK: edge entry -> then probability is 64 / 68
-; CHECK: edge entry -> else probability is 4 / 68
+; CHECK: edge entry -> then probability is 0x78787878 / 0x80000000 = 94.12% [HOT edge]
+; CHECK: edge entry -> else probability is 0x07878788 / 0x80000000 = 5.88%
 
 then:
   br label %exit
-; CHECK: edge then -> exit probability is 16 / 16 = 100%
+; CHECK: edge then -> exit probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
 
 else:
   br label %exit
-; CHECK: edge else -> exit probability is 16 / 16 = 100%
+; CHECK: edge else -> exit probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
 
 exit:
   %result = phi i32 [ %a, %then ], [ %b, %else ]
@@ -52,31 +52,31 @@ entry:
                                  i32 2, label %case_c
                                  i32 3, label %case_d
                                  i32 4, label %case_e ], !prof !1
-; CHECK: edge entry -> case_a probability is 4 / 80
-; CHECK: edge entry -> case_b probability is 4 / 80
-; CHECK: edge entry -> case_c probability is 64 / 80
-; CHECK: edge entry -> case_d probability is 4 / 80
-; CHECK: edge entry -> case_e probability is 4 / 80
+; CHECK: edge entry -> case_a probability is 0x06666666 / 0x80000000 = 5.00%
+; CHECK: edge entry -> case_b probability is 0x06666666 / 0x80000000 = 5.00%
+; CHECK: edge entry -> case_c probability is 0x66666666 / 0x80000000 = 80.00%
+; CHECK: edge entry -> case_d probability is 0x06666666 / 0x80000000 = 5.00%
+; CHECK: edge entry -> case_e probability is 0x06666666 / 0x80000000 = 5.00%
 
 case_a:
   br label %exit
-; CHECK: edge case_a -> exit probability is 16 / 16 = 100%
+; CHECK: edge case_a -> exit probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
 
 case_b:
   br label %exit
-; CHECK: edge case_b -> exit probability is 16 / 16 = 100%
+; CHECK: edge case_b -> exit probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
 
 case_c:
   br label %exit
-; CHECK: edge case_c -> exit probability is 16 / 16 = 100%
+; CHECK: edge case_c -> exit probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
 
 case_d:
   br label %exit
-; CHECK: edge case_d -> exit probability is 16 / 16 = 100%
+; CHECK: edge case_d -> exit probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
 
 case_e:
   br label %exit
-; CHECK: edge case_e -> exit probability is 16 / 16 = 100%
+; CHECK: edge case_e -> exit probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
 
 exit:
   %result = phi i32 [ %a, %case_a ],
@@ -99,9 +99,9 @@ entry:
     i64 2, label %sw.bb
     i64 5, label %sw.bb1
   ], !prof !2
-; CHECK: edge entry -> return probability is 7 / 85
-; CHECK: edge entry -> sw.bb probability is 14 / 85
-; CHECK: edge entry -> sw.bb1 probability is 64 / 85
+; CHECK: edge entry -> return probability is 0x0a8a8a8b / 0x80000000 = 8.24%
+; CHECK: edge entry -> sw.bb probability is 0x15151515 / 0x80000000 = 16.47%
+; CHECK: edge entry -> sw.bb1 probability is 0x60606060 / 0x80000000 = 75.29%
 
 sw.bb:
   br label %return
@@ -122,17 +122,17 @@ define i32 @test5(i32 %a, i32 %b, i1 %flag) {
 ; CHECK: Printing analysis {{.*}} for function 'test5'
 entry:
   br i1 %flag, label %then, label %else
-; CHECK: edge entry -> then probability is 4 / 68
-; CHECK: edge entry -> else probability is 64 / 68
+; CHECK: edge entry -> then probability is 0x07878788 / 0x80000000 = 5.88%
+; CHECK: edge entry -> else probability is 0x78787878 / 0x80000000 = 94.12% [HOT edge]
 
 then:
   call void @coldfunc()
   br label %exit
-; CHECK: edge then -> exit probability is 16 / 16 = 100%
+; CHECK: edge then -> exit probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
 
 else:
   br label %exit
-; CHECK: edge else -> exit probability is 16 / 16 = 100%
+; CHECK: edge else -> exit probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
 
 exit:
   %result = phi i32 [ %a, %then ], [ %b, %else ]
@@ -149,8 +149,8 @@ define i32 @test_cold_call_sites(i32* %a) {
 ; after that is fixed.
 
 ; CHECK: Printing analysis {{.*}} for function 'test_cold_call_sites'
-; CHECK: edge entry -> then probability is 4 / 68 = 5.88235%
-; CHECK: edge entry -> else probability is 64 / 68 = 94.1176% [HOT edge]
+; CHECK: edge entry -> then probability is 0x07878788 / 0x80000000 = 5.88%
+; CHECK: edge entry -> else probability is 0x78787878 / 0x80000000 = 94.12% [HOT edge]
 
 entry:
   %gep1 = getelementptr i32, i32* %a, i32 1
@@ -179,8 +179,8 @@ define i32 @zero1(i32 %i, i32 %a, i32 %b) {
 entry:
   %cond = icmp eq i32 %i, 0
   br i1 %cond, label %then, label %else
-; CHECK: edge entry -> then probability is 12 / 32
-; CHECK: edge entry -> else probability is 20 / 32
+; CHECK: edge entry -> then probability is 0x30000000 / 0x80000000 = 37.50%
+; CHECK: edge entry -> else probability is 0x50000000 / 0x80000000 = 62.50%
 
 then:
   br label %exit
@@ -198,8 +198,8 @@ define i32 @zero2(i32 %i, i32 %a, i32 %b) {
 entry:
   %cond = icmp ne i32 %i, -1
   br i1 %cond, label %then, label %else
-; CHECK: edge entry -> then probability is 20 / 32
-; CHECK: edge entry -> else probability is 12 / 32
+; CHECK: edge entry -> then probability is 0x50000000 / 0x80000000 = 62.50%
+; CHECK: edge entry -> else probability is 0x30000000 / 0x80000000 = 37.50%
 
 then:
   br label %exit
@@ -220,8 +220,8 @@ entry:
   %and = and i32 %i, 2
   %tobool = icmp eq i32 %and, 0
   br i1 %tobool, label %then, label %else
-; CHECK: edge entry -> then probability is 16 / 32
-; CHECK: edge entry -> else probability is 16 / 32
+; CHECK: edge entry -> then probability is 0x40000000 / 0x80000000 = 50.00%
+; CHECK: edge entry -> else probability is 0x40000000 / 0x80000000 = 50.00%
 
 then:
 ; AND'ing with other bitmask might be something else, so we still assume the
@@ -229,8 +229,8 @@ then:
   %and2 = and i32 %i, 5
   %tobool2 = icmp eq i32 %and2, 0
   br i1 %tobool2, label %else, label %exit
-; CHECK: edge then -> else probability is 12 / 32
-; CHECK: edge then -> exit probability is 20 / 32
+; CHECK: edge then -> else probability is 0x30000000 / 0x80000000 = 37.50%
+; CHECK: edge then -> exit probability is 0x50000000 / 0x80000000 = 62.50%
 
 else:
   br label %exit