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/branch.ll b/llvm/test/Transforms/SampleProfile/branch.ll
index aeb3671..25bd455 100644
--- a/llvm/test/Transforms/SampleProfile/branch.ll
+++ b/llvm/test/Transforms/SampleProfile/branch.ll
@@ -36,8 +36,8 @@
tail call void @llvm.dbg.value(metadata i8** %argv, i64 0, metadata !14, metadata !DIExpression()), !dbg !27
%cmp = icmp slt i32 %argc, 2, !dbg !28
br i1 %cmp, label %return, label %if.end, !dbg !28
-; CHECK: edge entry -> return probability is 1 / 2 = 50%
-; CHECK: edge entry -> if.end probability is 1 / 2 = 50%
+; CHECK: edge entry -> return probability is 0 / 1 = 0%
+; CHECK: edge entry -> if.end probability is 1 / 1 = 100%
if.end: ; preds = %entry
%arrayidx = getelementptr inbounds i8*, i8** %argv, i64 1, !dbg !30
@@ -46,8 +46,8 @@
tail call void @llvm.dbg.value(metadata i32 %call, i64 0, metadata !17, metadata !DIExpression()), !dbg !30
%cmp1 = icmp sgt i32 %call, 100, !dbg !35
br i1 %cmp1, label %for.body, label %if.end6, !dbg !35
-; CHECK: edge if.end -> for.body probability is 1 / 2 = 50%
-; CHECK: edge if.end -> if.end6 probability is 1 / 2 = 50%
+; CHECK: edge if.end -> for.body probability is 0 / 1 = 0%
+; CHECK: edge if.end -> if.end6 probability is 1 / 1 = 100%
for.body: ; preds = %if.end, %for.body
%u.016 = phi i32 [ %inc, %for.body ], [ 0, %if.end ]
@@ -65,8 +65,8 @@
tail call void @llvm.dbg.value(metadata i32 %inc, i64 0, metadata !21, metadata !DIExpression()), !dbg !38
%exitcond = icmp eq i32 %inc, %call, !dbg !38
br i1 %exitcond, label %if.end6, label %for.body, !dbg !38
-; CHECK: edge for.body -> if.end6 probability is 1 / 10227 = 0.00977804
-; CHECK: edge for.body -> for.body probability is 10226 / 10227 = 99.9902% [HOT edge]
+; CHECK: edge for.body -> if.end6 probability is 0 / 10226 = 0%
+; CHECK: edge for.body -> for.body probability is 10226 / 10226 = 100% [HOT edge]
if.end6: ; preds = %for.body, %if.end
%result.0 = phi double [ 0.000000e+00, %if.end ], [ %sub, %for.body ]
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
diff --git a/llvm/test/Transforms/SampleProfile/propagate.ll b/llvm/test/Transforms/SampleProfile/propagate.ll
index 8ee1e09..620d125 100644
--- a/llvm/test/Transforms/SampleProfile/propagate.ll
+++ b/llvm/test/Transforms/SampleProfile/propagate.ll
@@ -73,8 +73,8 @@
%5 = load i64, i64* %N.addr, align 8, !dbg !15
%cmp1 = icmp slt i64 %4, %5, !dbg !15
br i1 %cmp1, label %for.body, label %for.end18, !dbg !15
-; CHECK: edge for.cond -> for.body probability is 10 / 11 = 90.9091% [HOT edge]
-; CHECK: edge for.cond -> for.end18 probability is 1 / 11 = 9.09091%
+; CHECK: edge for.cond -> for.body probability is 10 / 10 = 100% [HOT edge]
+; CHECK: edge for.cond -> for.end18 probability is 0 / 10 = 0%
for.body: ; preds = %for.cond
%6 = load i64, i64* %i, align 8, !dbg !18
@@ -119,8 +119,8 @@
%14 = load i64, i64* %i, align 8, !dbg !28
%cmp10 = icmp slt i64 %conv9, %14, !dbg !28
br i1 %cmp10, label %for.body11, label %for.end, !dbg !28
-; CHECK: edge for.cond8 -> for.body11 probability is 16191 / 16192 = 99.9938% [HOT edge]
-; CHECK: edge for.cond8 -> for.end probability is 1 / 16192 = 0.00617589%
+; CHECK: edge for.cond8 -> for.body11 probability is 16191 / 16191 = 100% [HOT edge]
+; CHECK: edge for.cond8 -> for.end probability is 0 / 16191 = 0%
for.body11: ; preds = %for.cond8
%15 = load i32, i32* %j, align 4, !dbg !31