[llvm-commits] [llvm] r147142 - in /llvm/trunk: lib/Analysis/BranchProbabilityInfo.cpp test/Analysis/BranchProbabilityInfo/noreturn.ll

[Chandler Carruth]

Author: chandlerc
Date: Thu Dec 22 03:26:37 2011
New Revision: 147142

URL: http://llvm.org/viewvc/llvm-project?rev=147142&view=rev
Log:
Make the unreachable probability much much heavier. The previous
probability wouldn't be considered "hot" in some weird loop structures
or other compounding probability patterns. This makes it much harder to
confuse, but isn't really a principled fix. I'd actually like it if we
could model a zero probability, as it would make this much easier to
reason about. Suggestions for how to do this better are welcome.

Modified:
    llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp
    llvm/trunk/test/Analysis/BranchProbabilityInfo/noreturn.ll

Modified: llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp?rev=147142&r1=147141&r2=147142&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp (original)
+++ llvm/trunk/lib/Analysis/BranchProbabilityInfo.cpp Thu Dec 22 03:26:37 2011
@@ -65,8 +65,9 @@
 ///
 /// This is the weight for a branch not being taken toward a block that
 /// terminates (eventually) in unreachable. Such a branch is essentially never
-/// taken.
-static const uint32_t UR_NONTAKEN_WEIGHT = 1023;
+/// taken. Set the weight to an absurdly high value so that nested loops don't
+/// easily subsume it.
+static const uint32_t UR_NONTAKEN_WEIGHT = 1024*1024 - 1;
 
 static const uint32_t PH_TAKEN_WEIGHT = 20;
 static const uint32_t PH_NONTAKEN_WEIGHT = 12;

Modified: llvm/trunk/test/Analysis/BranchProbabilityInfo/noreturn.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BranchProbabilityInfo/noreturn.ll?rev=147142&r1=147141&r2=147142&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/BranchProbabilityInfo/noreturn.ll (original)
+++ llvm/trunk/test/Analysis/BranchProbabilityInfo/noreturn.ll Thu Dec 22 03:26:37 2011
@@ -8,8 +8,8 @@
 entry:
   %cond = icmp eq i32 %a, 42
   br i1 %cond, label %exit, label %abort
-; CHECK: edge entry -> exit probability is 1023 / 1024
-; CHECK: edge entry -> abort probability is 1 / 1024
+; CHECK: edge entry -> exit probability is 1048575 / 1048576
+; CHECK: edge entry -> abort probability is 1 / 1048576
 
 abort:
   call void @abort() noreturn
@@ -26,11 +26,11 @@
                               i32 2, label %case_b
                               i32 3, label %case_c
                               i32 4, label %case_d]
-; CHECK: edge entry -> exit probability is 1023 / 1027
-; CHECK: edge entry -> case_a probability is 1 / 1027
-; CHECK: edge entry -> case_b probability is 1 / 1027
-; CHECK: edge entry -> case_c probability is 1 / 1027
-; CHECK: edge entry -> case_d probability is 1 / 1027
+; CHECK: edge entry -> exit probability is 1048575 / 1048579
+; CHECK: edge entry -> case_a probability is 1 / 1048579
+; CHECK: edge entry -> case_b probability is 1 / 1048579
+; CHECK: edge entry -> case_c probability is 1 / 1048579
+; CHECK: edge entry -> case_d probability is 1 / 1048579
 
 case_a:
   br label %case_b
@@ -55,8 +55,8 @@
 entry:
   %cond1 = icmp eq i32 %a, 42
   br i1 %cond1, label %exit, label %dom
-; CHECK: edge entry -> exit probability is 1023 / 1024
-; CHECK: edge entry -> dom probability is 1 / 1024
+; CHECK: edge entry -> exit probability is 1048575 / 1048576
+; CHECK: edge entry -> dom probability is 1 / 1048576
 
 dom:
   %cond2 = icmp ult i32 %a, 42