Allow 0-weight branches in BranchProbabilityInfo.
Summary:
When computing branch weights in BPI, we used to disallow branches with
weight 0. This is a minor nuisance, because a branch with weight 0 is
different to "don't have information". In the context of
instrumentation, it may mean "never executed", in the context of
sampling, it means "never or seldom executed".
In allowing 0 weight branches, I ran into issues with the switch
expansion code in selection DAG. It is currently hardwired to not handle
branches with weight 0. To maintain the current behaviour, I changed it
to use 1 when it finds 0, but perhaps the algorithm needs changes to
tolerate branches with weight zero.
Reviewers: hansw
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D9533
llvm-svn: 236617
diff --git a/llvm/test/Transforms/SampleProfile/calls.ll b/llvm/test/Transforms/SampleProfile/calls.ll
index a6ad344..10f43a1 100644
--- a/llvm/test/Transforms/SampleProfile/calls.ll
+++ b/llvm/test/Transforms/SampleProfile/calls.ll
@@ -52,8 +52,8 @@
store i32 %inc, i32* %i, align 4, !dbg !14
%cmp = icmp slt i32 %0, 400000000, !dbg !14
br i1 %cmp, label %while.body, label %while.end, !dbg !14
-; CHECK: edge while.cond -> while.body probability is 5391 / 5392 = 99.9815% [HOT edge]
-; CHECK: edge while.cond -> while.end probability is 1 / 5392 = 0.018546%
+; CHECK: edge while.cond -> while.body probability is 5391 / 5391 = 100% [HOT edge]
+; CHECK: edge while.cond -> while.end probability is 0 / 5391 = 0%
while.body: ; preds = %while.cond
%1 = load i32, i32* %i, align 4, !dbg !16
@@ -63,8 +63,8 @@
; both branches out of while.body had the same weight. In reality,
; the edge while.body->if.then is taken most of the time.
;
-; CHECK: edge while.body -> if.then probability is 5752 / 5753 = 99.9826% [HOT edge]
-; CHECK: edge while.body -> if.else probability is 1 / 5753 = 0.0173822%
+; CHECK: edge while.body -> if.then probability is 5752 / 5752 = 100% [HOT edge]
+; CHECK: edge while.body -> if.else probability is 0 / 5752 = 0%
if.then: ; preds = %while.body