PGO: Scale large counters down to 32-bits

PGO counters are 64-bit and branch weights are 32-bit.  Scale them down
when necessary, instead of just taking the lower 32 bits.

<rdar://problem/16276448>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203592 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 49 insertions, 0 deletions

diff --git a/test/Profile/c-counter-overflows.c b/test/Profile/c-counter-overflows.c
new file mode 100644
index 0000000000..ddbe6d1c97
--- /dev/null
+++ b/test/Profile/c-counter-overflows.c
@@ -0,0 +1,49 @@
+// Test that big branch weights get scaled down to 32-bits, rather than just
+// truncated.
+
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.9 -main-file-name c-counter-overflows.c %s -o - -emit-llvm -fprofile-instr-use=%S/Inputs/c-counter-overflows.profdata | FileCheck %s
+
+#include <stdint.h>
+
+// PGOGEN: @[[MAIN:__llvm_pgo_ctr[0-9]*]] = private global [2 x i64] zeroinitializer
+int main(int argc, const char *argv[]) {
+  // Need counts higher than 32-bits.
+  // CHECK: br {{.*}} !prof ![[FOR:[0-9]+]]
+  // max   = 0xffffffff0
+  // scale = 0xffffffff0 / 0xffffffff + 1 = 17
+  // loop-body: 0xffffffff0 / 17 + 1 = 0xf0f0f0f0 + 1 = 4042322161 => -252645135
+  // loop-exit: 0x000000001 / 17 + 1 = 0x00000000 + 1 =          1 =>          1
+  for (uint64_t I = 0; I < 0xffffffff0; ++I) {
+    // max   = 0xffffffff * 15 = 0xefffffff1
+    // scale = 0xefffffff1 / 0xffffffff + 1 = 16
+    // CHECK: br {{.*}} !prof ![[IF:[0-9]+]]
+    if (I & 0xf) {
+      // 0xefffffff1 / 16 + 1 = 0xefffffff + 1 = 4026531840 => -268435456
+    } else {
+      // 0x0ffffffff / 16 + 1 = 0x0fffffff + 1 =  268435456 =>  268435456
+    }
+
+    // max   = 0xffffffff * 5 = 0x4fffffffb
+    // scale = 0x4fffffffb / 0xffffffff + 1 = 6
+    // CHECK: ], !prof ![[SWITCH:[0-9]+]]
+    switch ((I & 0xf) / 5) {
+    case 0:
+      // 0x4fffffffb / 6 = 0xd5555554 + 1 = 3579139413 => -715827883
+      break;
+    case 1:
+      // 0x4fffffffb / 6 = 0xd5555554 + 1 = 3579139413 => -715827883
+      break;
+    case 2:
+      // 0x4fffffffb / 6 = 0xd5555554 + 1 = 3579139413 => -715827883
+      break;
+    default:
+      // 0x0ffffffff / 6 = 0x2aaaaaaa + 1 =  715827883 =>  715827883
+      break;
+    }
+  }
+  return 0;
+}
+
+// CHECK-DAG: ![[FOR]] = metadata !{metadata !"branch_weights", i32 -252645135, i32 1}
+// CHECK-DAG: ![[IF]]  = metadata !{metadata !"branch_weights", i32 -268435456, i32 268435456}
+// CHECK-DAG: ![[SWITCH]] = metadata !{metadata !"branch_weights", i32 715827883, i32 -715827883, i32 -715827883, i32 -715827883}