[PowerPC] Check hot loop exit edge in PPCCTRLoops

PPCCTRLoops transform loops using mtctr/bdnz instructions if loop trip count is known and big enough to compensate for the cost of mtctr.
But if there is a loop exit edge which is known to be frequently taken (by builtin_expect or by PGO), we should not transform the loop to avoid the cost of mtctr instruction. Here is an example of a loop with hot exit edge:

for (unsigned i = 0; i < TripCount; i++) {
  // do something
  if (__builtin_expect(check(), 1))
    break;
  // do something
}

Differential Revision: https://reviews.llvm.org/D42637

llvm-svn: 324229

1 files changed, 187 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/PowerPC/ctrloops-hot-exit.ll b/llvm/test/CodeGen/PowerPC/ctrloops-hot-exit.ll
new file mode 100644
index 00000000000..6bb4113f07e
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/ctrloops-hot-exit.ll
@@ -0,0 +1,187 @@
+; RUN: llc -verify-machineinstrs -mtriple=powerpc64le-unknown-linux-gnu -mcpu=pwr9 < %s | FileCheck %s
+
+; If there is an exit edge known to be frequently taken,
+; we should not transform this loop.
+
+; A loop having a hot exit edge (exit in false branch)
+define signext i64 @func() {
+; CHECK: @func
+; CHECK-NOT: mtctr
+; CHECK-NOT: bdnz
+
+entry:
+  %a = alloca [1000 x i32], align 4
+  %0 = bitcast [1000 x i32]* %a to i8*
+  br label %for.body
+
+for.body:
+  %i.013 = phi i64 [ 0, %entry ], [ %inc, %if.end ]
+  %b.012 = phi i64 [ 0, %entry ], [ %xor, %if.end ]
+  %arrayidx = getelementptr inbounds [1000 x i32], [1000 x i32]* %a, i64 0, i64 %i.013
+  %1 = load i32, i32* %arrayidx, align 4
+  %tobool = icmp eq i32 %1, 0
+  br i1 %tobool, label %if.end, label %cleanup, !prof !1
+
+if.end:
+  %xor = xor i64 %i.013, %b.012
+  %inc = add nuw nsw i64 %i.013, 1
+  %cmp = icmp ult i64 %inc, 1000
+  br i1 %cmp, label %for.body, label %cleanup
+
+cleanup:
+  %res = phi i64 [ %b.012, %for.body ], [ %xor, %if.end ]
+  ret i64 %res
+}
+
+; A loop having a cold exit edge (exit in false branch)
+define signext i64 @func2() {
+; CHECK: @func2
+; CHECK: mtctr
+; CHECK: bdnz
+
+entry:
+  %a = alloca [1000 x i32], align 4
+  %0 = bitcast [1000 x i32]* %a to i8*
+  br label %for.body
+
+for.body:
+  %i.013 = phi i64 [ 0, %entry ], [ %inc, %if.end ]
+  %b.012 = phi i64 [ 0, %entry ], [ %xor, %if.end ]
+  %arrayidx = getelementptr inbounds [1000 x i32], [1000 x i32]* %a, i64 0, i64 %i.013
+  %1 = load i32, i32* %arrayidx, align 4
+  %tobool = icmp eq i32 %1, 0
+  br i1 %tobool, label %if.end, label %cleanup, !prof !2
+
+if.end:
+  %xor = xor i64 %i.013, %b.012
+  %inc = add nuw nsw i64 %i.013, 1
+  %cmp = icmp ult i64 %inc, 1000
+  br i1 %cmp, label %for.body, label %cleanup
+
+cleanup:
+  %res = phi i64 [ %b.012, %for.body ], [ %xor, %if.end ]
+  ret i64 %res
+}
+
+; A loop having an exit edge without profile data  (exit in false branch)
+define signext i64 @func3() {
+; CHECK: @func3
+; CHECK: mtctr
+; CHECK: bdnz
+
+entry:
+  %a = alloca [1000 x i32], align 4
+  %0 = bitcast [1000 x i32]* %a to i8*
+  br label %for.body
+
+for.body:
+  %i.013 = phi i64 [ 0, %entry ], [ %inc, %if.end ]
+  %b.012 = phi i64 [ 0, %entry ], [ %xor, %if.end ]
+  %arrayidx = getelementptr inbounds [1000 x i32], [1000 x i32]* %a, i64 0, i64 %i.013
+  %1 = load i32, i32* %arrayidx, align 4
+  %tobool = icmp eq i32 %1, 0
+  br i1 %tobool, label %if.end, label %cleanup
+
+if.end:
+  %xor = xor i64 %i.013, %b.012
+  %inc = add nuw nsw i64 %i.013, 1
+  %cmp = icmp ult i64 %inc, 1000
+  br i1 %cmp, label %for.body, label %cleanup
+
+cleanup:
+  %res = phi i64 [ %b.012, %for.body ], [ %xor, %if.end ]
+  ret i64 %res
+}
+
+; A loop having a hot exit edge (exit in true branch)
+define signext i64 @func4() {
+; CHECK: @func4
+; CHECK-NOT: mtctr
+; CHECK-NOT: bdnz
+
+entry:
+  %a = alloca [1000 x i32], align 4
+  %0 = bitcast [1000 x i32]* %a to i8*
+  br label %for.body
+
+for.body:
+  %i.013 = phi i64 [ 0, %entry ], [ %inc, %if.end ]
+  %b.012 = phi i64 [ 0, %entry ], [ %xor, %if.end ]
+  %arrayidx = getelementptr inbounds [1000 x i32], [1000 x i32]* %a, i64 0, i64 %i.013
+  %1 = load i32, i32* %arrayidx, align 4
+  %tobool = icmp ne i32 %1, 0
+  br i1 %tobool, label %cleanup, label %if.end, !prof !2
+
+if.end:
+  %xor = xor i64 %i.013, %b.012
+  %inc = add nuw nsw i64 %i.013, 1
+  %cmp = icmp ult i64 %inc, 1000
+  br i1 %cmp, label %for.body, label %cleanup
+
+cleanup:
+  %res = phi i64 [ %b.012, %for.body ], [ %xor, %if.end ]
+  ret i64 %res
+}
+
+; A loop having a cold exit edge (exit in true branch)
+define signext i64 @func5() {
+; CHECK: @func5
+; CHECK: mtctr
+; CHECK: bdnz
+
+entry:
+  %a = alloca [1000 x i32], align 4
+  %0 = bitcast [1000 x i32]* %a to i8*
+  br label %for.body
+
+for.body:
+  %i.013 = phi i64 [ 0, %entry ], [ %inc, %if.end ]
+  %b.012 = phi i64 [ 0, %entry ], [ %xor, %if.end ]
+  %arrayidx = getelementptr inbounds [1000 x i32], [1000 x i32]* %a, i64 0, i64 %i.013
+  %1 = load i32, i32* %arrayidx, align 4
+  %tobool = icmp ne i32 %1, 0
+  br i1 %tobool, label %cleanup, label %if.end, !prof !1
+
+if.end:
+  %xor = xor i64 %i.013, %b.012
+  %inc = add nuw nsw i64 %i.013, 1
+  %cmp = icmp ult i64 %inc, 1000
+  br i1 %cmp, label %for.body, label %cleanup
+
+cleanup:
+  %res = phi i64 [ %b.012, %for.body ], [ %xor, %if.end ]
+  ret i64 %res
+}
+
+; A loop having an exit edge without profile data  (exit in true branch)
+define signext i64 @func6() {
+; CHECK: @func6
+; CHECK: mtctr
+; CHECK: bdnz
+
+entry:
+  %a = alloca [1000 x i32], align 4
+  %0 = bitcast [1000 x i32]* %a to i8*
+  br label %for.body
+
+for.body:
+  %i.013 = phi i64 [ 0, %entry ], [ %inc, %if.end ]
+  %b.012 = phi i64 [ 0, %entry ], [ %xor, %if.end ]
+  %arrayidx = getelementptr inbounds [1000 x i32], [1000 x i32]* %a, i64 0, i64 %i.013
+  %1 = load i32, i32* %arrayidx, align 4
+  %tobool = icmp ne i32 %1, 0
+  br i1 %tobool, label %cleanup, label %if.end
+
+if.end:
+  %xor = xor i64 %i.013, %b.012
+  %inc = add nuw nsw i64 %i.013, 1
+  %cmp = icmp ult i64 %inc, 1000
+  br i1 %cmp, label %for.body, label %cleanup
+
+cleanup:
+  %res = phi i64 [ %b.012, %for.body ], [ %xor, %if.end ]
+  ret i64 %res
+}
+
+!1 = !{!"branch_weights", i32 1, i32 2000}
+!2 = !{!"branch_weights", i32 2000, i32 1}