[PowerPC] Add Branch Hints for Highly-Biased Branches

This branch adds hints for highly biased branches on the PPC architecture. Even
in absence of profiling information, LLVM will mark code reaching unreachable
terminators and other exceptional control flow constructs as highly unlikely to
be reached.

Patch by Tom Jablin!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255398 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 135 insertions, 0 deletions

diff --git a/test/CodeGen/PowerPC/branch-hint.ll b/test/CodeGen/PowerPC/branch-hint.ll
new file mode 100644
index 00000000000..46160507105
--- /dev/null
+++ b/test/CodeGen/PowerPC/branch-hint.ll
@@ -0,0 +1,135 @@
+; RUN: llc < %s -O1 -verify-machineinstrs -mtriple=powerpc64-unknown-linux-gnu -ppc-use-branch-hint=false | FileCheck %s
+; RUN: llc < %s -O1 -verify-machineinstrs -mtriple=powerpc64-unknown-linux-gnu -ppc-use-branch-hint=true | FileCheck %s -check-prefix=CHECK-HINT
+define void @branch_hint_1(i32 %src) {
+entry:
+  %cmp = icmp eq i32 %src, 0
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:
+  tail call void @foo() #0
+  unreachable
+
+if.end:
+  call void @goo()
+  ret void
+
+; CHECK-LABEL: branch_hint_1:
+; CHECK: beq
+
+; CHECK-HINT-LABEL: branch_hint_1:
+; CHECK-HINT: beq-
+}
+
+define void @branch_hint_2(i32 %src) {
+entry:
+  %cmp = icmp eq i32 %src, 0
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:
+  call void @goo()
+  ret void
+
+if.end:
+  tail call void @foo() #0
+  unreachable
+
+; CHECK-LABEL: @branch_hint_2
+; CHECK: bne
+
+; CHECK-HINT-LABEL: @branch_hint_2
+; CHECK-HINT: bne-
+}
+
+declare void @foo()
+attributes #0 = { noreturn }
+
+define void @branch_hint_3(i32 %src) {
+entry:
+  %cmp = icmp eq i32 %src, 0
+  br i1 %cmp, label %if.then, label %if.end, !prof !0
+
+if.then:
+  call void @foo()
+  ret void
+
+if.end:
+  call void @goo()
+  ret void
+
+; CHECK-LABEL: @branch_hint_3
+; CHECK: bne
+
+; CHECK-HINT-LABEL: @branch_hint_3
+; CHECK-HINT: bne
+}
+
+!0 = !{!"branch_weights", i32 64, i32 4}
+
+define void @branch_hint_4(i32 %src) {
+entry:
+  %cmp = icmp eq i32 %src, 0
+  br i1 %cmp, label %if.then, label %if.end, !prof !1
+
+if.then:
+  call void @foo()
+  ret void
+
+if.end:
+  call void @goo()
+  ret void
+
+; CHECK-HINT-LABEL: branch_hint_4
+; CHECK-HINT: bne
+}
+
+!1 = !{!"branch_weights", i32 64, i32 8}
+
+define void @branch_hint_5(i32 %src) {
+entry:
+  %cmp = icmp eq i32 %src, 0
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:
+  ret void
+
+if.end:
+  call void @goo()
+  ret void
+
+; CHECK-HINT-LABEL: branch_hint_5:
+; CHECK-HINT: beq
+}
+
+declare void @goo()
+
+define void @branch_hint_6(i32 %src1, i32 %src2, i32 %src3) {
+entry:
+  %cmp = icmp eq i32 %src1, 0
+  br i1 %cmp, label %if.end.6, label %if.end, !prof !3
+
+if.end:
+  %cmp1 = icmp eq i32 %src2, 0
+  br i1 %cmp1, label %if.end.3, label %if.then.2
+
+if.then.2:
+  tail call void @foo() #0
+  unreachable
+
+if.end.3:
+  %cmp4 = icmp eq i32 %src3, 1
+  br i1 %cmp4, label %if.then.5, label %if.end.6
+
+if.then.5:
+  tail call void @foo() #0
+  unreachable
+
+if.end.6:
+  ret void
+
+; CHECK-HINT-LABEL: branch_hint_6:
+; CHECK-HINT: bne
+; CHECK-HINT: bne-
+; CHECK-HINT: bne+
+}
+
+!3 = !{!"branch_weights", i32 64, i32 4}