[PATCH] D30633: [BPI] Unreachable branch has 0 probability

[Serguei Katkov via Phabricator via llvm-commits]

skatkov created this revision.

As unlikely as possible is actually 0 probability.
So let's use 0 as UR_TAKEN_WEIGHT constant.


https://reviews.llvm.org/D30633

Files:
  lib/Analysis/BranchProbabilityInfo.cpp
  test/Analysis/BranchProbabilityInfo/deopt-intrinsic.ll
  test/Analysis/BranchProbabilityInfo/noreturn.ll
  test/CodeGen/X86/switch-order-weight.ll


Index: test/CodeGen/X86/switch-order-weight.ll
===================================================================
--- test/CodeGen/X86/switch-order-weight.ll
+++ test/CodeGen/X86/switch-order-weight.ll
@@ -13,8 +13,8 @@
 ; CHECK-LABEL: test1:
 ; CHECK-NOT: unr
 ; CHECK: cmpl $10
-; CHECK: cmpl $20
 ; CHECK: bar
+; CHECK: cmpl $20
 
 if.then:
   tail call void @unr(i32 23) noreturn nounwind
Index: test/Analysis/BranchProbabilityInfo/noreturn.ll
===================================================================
--- test/Analysis/BranchProbabilityInfo/noreturn.ll
+++ test/Analysis/BranchProbabilityInfo/noreturn.ll
@@ -9,8 +9,8 @@
 entry:
   %cond = icmp eq i32 %a, 42
   br i1 %cond, label %exit, label %abort
-; CHECK: edge entry -> exit probability is 0x7ffff800 / 0x80000000 = 100.00% [HOT edge]
-; CHECK: edge entry -> abort probability is 0x00000800 / 0x80000000 = 0.00%
+; CHECK: edge entry -> exit probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
+; CHECK: edge entry -> abort probability is 0x00000000 / 0x80000000 = 0.00%
 
 abort:
   call void @abort() noreturn
@@ -27,11 +27,11 @@
                               i32 2, label %case_b
                               i32 3, label %case_c
                               i32 4, label %case_d]
-; CHECK: edge entry -> exit probability is 0x7ffff800 / 0x80000000 = 100.00% [HOT edge]
-; CHECK: edge entry -> case_a probability is 0x00000200 / 0x80000000 = 0.00%
-; CHECK: edge entry -> case_b probability is 0x00000200 / 0x80000000 = 0.00%
-; CHECK: edge entry -> case_c probability is 0x00000200 / 0x80000000 = 0.00%
-; CHECK: edge entry -> case_d probability is 0x00000200 / 0x80000000 = 0.00%
+; CHECK: edge entry -> exit probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
+; CHECK: edge entry -> case_a probability is 0x00000000 / 0x80000000 = 0.00%
+; CHECK: edge entry -> case_b probability is 0x00000000 / 0x80000000 = 0.00%
+; CHECK: edge entry -> case_c probability is 0x00000000 / 0x80000000 = 0.00%
+; CHECK: edge entry -> case_d probability is 0x00000000 / 0x80000000 = 0.00%
 
 case_a:
   br label %case_b
@@ -56,8 +56,8 @@
 entry:
   %cond1 = icmp eq i32 %a, 42
   br i1 %cond1, label %exit, label %dom
-; CHECK: edge entry -> exit probability is 0x7ffff800 / 0x80000000 = 100.00% [HOT edge]
-; CHECK: edge entry -> dom probability is 0x00000800 / 0x80000000 = 0.00%
+; CHECK: edge entry -> exit probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
+; CHECK: edge entry -> dom probability is 0x00000000 / 0x80000000 = 0.00%
 
 dom:
   %cond2 = icmp ult i32 %a, 42
@@ -87,8 +87,8 @@
 entry:
   %cmp = icmp sge i32 %idx, %limit
   br i1 %cmp, label %if.then, label %if.end
-; CHECK: edge entry -> if.then probability is 0x00000800 / 0x80000000 = 0.00%
-; CHECK: edge entry -> if.end probability is 0x7ffff800 / 0x80000000 = 100.00% [HOT edge]
+; CHECK: edge entry -> if.then probability is 0x00000000 / 0x80000000 = 0.00%
+; CHECK: edge entry -> if.end probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
 
 if.then:                                          ; preds = %entry
   %exception = call i8* @__cxa_allocate_exception(i64 1) #0
Index: test/Analysis/BranchProbabilityInfo/deopt-intrinsic.ll
===================================================================
--- test/Analysis/BranchProbabilityInfo/deopt-intrinsic.ll
+++ test/Analysis/BranchProbabilityInfo/deopt-intrinsic.ll
@@ -9,8 +9,8 @@
   %cond = icmp eq i32 %a, 42
   br i1 %cond, label %exit, label %deopt
 
-; CHECK:  edge entry -> exit probability is 0x7ffff800 / 0x80000000 = 100.00% [HOT edge]
-; CHECK:  edge entry -> deopt probability is 0x00000800 / 0x80000000 = 0.00%
+; CHECK:  edge entry -> exit probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
+; CHECK:  edge entry -> deopt probability is 0x00000000 / 0x80000000 = 0.00%
 
 deopt:
   %rval = call i32(...) @llvm.experimental.deoptimize.i32() [ "deopt"() ]
Index: lib/Analysis/BranchProbabilityInfo.cpp
===================================================================
--- lib/Analysis/BranchProbabilityInfo.cpp
+++ lib/Analysis/BranchProbabilityInfo.cpp
@@ -62,7 +62,7 @@
 ///
 /// This is the weight for a branch being taken to a block that terminates
 /// (eventually) in unreachable. These are predicted as unlikely as possible.
-static const uint32_t UR_TAKEN_WEIGHT = 1;
+static const uint32_t UR_TAKEN_WEIGHT = 0;
 
 /// \brief Unreachable-terminating branch not-taken weight.
 ///


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