diff options
Diffstat (limited to 'test/Analysis/BlockFrequencyInfo/irreducible.ll')
-rw-r--r-- | test/Analysis/BlockFrequencyInfo/irreducible.ll | 197 |
1 files changed, 197 insertions, 0 deletions
diff --git a/test/Analysis/BlockFrequencyInfo/irreducible.ll b/test/Analysis/BlockFrequencyInfo/irreducible.ll new file mode 100644 index 0000000000..46a2958700 --- /dev/null +++ b/test/Analysis/BlockFrequencyInfo/irreducible.ll @@ -0,0 +1,197 @@ +; RUN: opt < %s -analyze -block-freq | FileCheck %s + +; A loop with multiple exits should be handled correctly. +; +; CHECK-LABEL: Printing analysis {{.*}} for function 'multiexit': +; CHECK-NEXT: block-frequency-info: multiexit +define void @multiexit(i32 %a) { +; CHECK-NEXT: entry: float = 1.0, int = [[ENTRY:[0-9]+]] +entry: + br label %loop.1 + +; CHECK-NEXT: loop.1: float = 1.333{{3*}}, +loop.1: + %i = phi i32 [ 0, %entry ], [ %inc.2, %loop.2 ] + call void @f(i32 %i) + %inc.1 = add i32 %i, 1 + %cmp.1 = icmp ugt i32 %inc.1, %a + br i1 %cmp.1, label %exit.1, label %loop.2, !prof !0 + +; CHECK-NEXT: loop.2: float = 0.666{{6*7}}, +loop.2: + call void @g(i32 %inc.1) + %inc.2 = add i32 %inc.1, 1 + %cmp.2 = icmp ugt i32 %inc.2, %a + br i1 %cmp.2, label %exit.2, label %loop.1, !prof !1 + +; CHECK-NEXT: exit.1: float = 0.666{{6*7}}, +exit.1: + call void @h(i32 %inc.1) + br label %return + +; CHECK-NEXT: exit.2: float = 0.333{{3*}}, +exit.2: + call void @i(i32 %inc.2) + br label %return + +; CHECK-NEXT: return: float = 1.0, int = [[ENTRY]] +return: + ret void +} + +declare void @f(i32 %x) +declare void @g(i32 %x) +declare void @h(i32 %x) +declare void @i(i32 %x) + +!0 = metadata !{metadata !"branch_weights", i32 3, i32 3} +!1 = metadata !{metadata !"branch_weights", i32 5, i32 5} + +; The current BlockFrequencyInfo algorithm doesn't handle multiple entrances +; into a loop very well. The frequencies assigned to blocks in the loop are +; predictable (and not absurd), but also not correct and therefore not worth +; testing. +; +; There are two testcases below. +; +; For each testcase, I use a CHECK-NEXT/NOT combo like an XFAIL with the +; granularity of a single check. If/when this behaviour is fixed, we'll know +; about it, and the test should be updated. +; +; Testcase #1 +; =========== +; +; In this case c1 and c2 should have frequencies of 15/7 and 13/7, +; respectively. To calculate this, consider assigning 1.0 to entry, and +; distributing frequency iteratively (to infinity). At the first iteration, +; entry gives 3/4 to c1 and 1/4 to c2. At every step after, c1 and c2 give 3/4 +; of what they have to each other. Somehow, all of it comes out to exit. +; +; c1 = 3/4 + 1/4*3/4 + 3/4*3^2/4^2 + 1/4*3^3/4^3 + 3/4*3^3/4^3 + ... +; c2 = 1/4 + 3/4*3/4 + 1/4*3^2/4^2 + 3/4*3^3/4^3 + 1/4*3^3/4^3 + ... +; +; Simplify by splitting up the odd and even terms of the series and taking out +; factors so that the infite series matches: +; +; c1 = 3/4 *(9^0/16^0 + 9^1/16^1 + 9^2/16^2 + ...) +; + 3/16*(9^0/16^0 + 9^1/16^1 + 9^2/16^2 + ...) +; c2 = 1/4 *(9^0/16^0 + 9^1/16^1 + 9^2/16^2 + ...) +; + 9/16*(9^0/16^0 + 9^1/16^1 + 9^2/16^2 + ...) +; +; c1 = 15/16*(9^0/16^0 + 9^1/16^1 + 9^2/16^2 + ...) +; c2 = 13/16*(9^0/16^0 + 9^1/16^1 + 9^2/16^2 + ...) +; +; Since this geometric series sums to 16/7: +; +; c1 = 15/7 +; c2 = 13/7 +; +; If we treat c1 and c2 as members of the same loop, the exit frequency of the +; loop as a whole is 1/4, so the loop scale should be 4. Summing c1 and c2 +; gives 28/7, or 4.0, which is nice confirmation of the math above. +; +; However, assuming c1 precedes c2 in reverse post-order, the current algorithm +; returns 3/4 and 13/16, respectively. LoopInfo ignores edges between loops +; (and doesn't see any loops here at all), and -block-freq ignores the +; irreducible edge from c2 to c1. +; +; CHECK-LABEL: Printing analysis {{.*}} for function 'multientry': +; CHECK-NEXT: block-frequency-info: multientry +define void @multientry(i32 %a) { +; CHECK-NEXT: entry: float = 1.0, int = [[ENTRY:[0-9]+]] +entry: + %choose = call i32 @choose(i32 %a) + %compare = icmp ugt i32 %choose, %a + br i1 %compare, label %c1, label %c2, !prof !2 + +; This is like a single-line XFAIL (see above). +; CHECK-NEXT: c1: +; CHECK-NOT: float = 2.142857{{[0-9]*}}, +c1: + %i1 = phi i32 [ %a, %entry ], [ %i2.inc, %c2 ] + %i1.inc = add i32 %i1, 1 + %choose1 = call i32 @choose(i32 %i1) + %compare1 = icmp ugt i32 %choose1, %a + br i1 %compare1, label %c2, label %exit, !prof !2 + +; This is like a single-line XFAIL (see above). +; CHECK-NEXT: c2: +; CHECK-NOT: float = 1.857142{{[0-9]*}}, +c2: + %i2 = phi i32 [ %a, %entry ], [ %i1.inc, %c1 ] + %i2.inc = add i32 %i2, 1 + %choose2 = call i32 @choose(i32 %i2) + %compare2 = icmp ugt i32 %choose2, %a + br i1 %compare2, label %c1, label %exit, !prof !2 + +; We still shouldn't lose any frequency. +; CHECK-NEXT: exit: float = 1.0, int = [[ENTRY]] +exit: + ret void +} + +; Testcase #2 +; =========== +; +; In this case c1 and c2 should be treated as equals in a single loop. The +; exit frequency is 1/3, so the scaling factor for the loop should be 3.0. The +; loop is entered 2/3 of the time, and c1 and c2 split the total loop frequency +; evenly (1/2), so they should each have frequencies of 1.0 (3.0*2/3*1/2). +; Another way of computing this result is by assigning 1.0 to entry and showing +; that c1 and c2 should accumulate frequencies of: +; +; 1/3 + 2/9 + 4/27 + 8/81 + ... +; 2^0/3^1 + 2^1/3^2 + 2^2/3^3 + 2^3/3^4 + ... +; +; At the first step, c1 and c2 each get 1/3 of the entry. At each subsequent +; step, c1 and c2 each get 1/3 of what's left in c1 and c2 combined. This +; infinite series sums to 1. +; +; However, assuming c1 precedes c2 in reverse post-order, the current algorithm +; returns 1/2 and 3/4, respectively. LoopInfo ignores edges between loops (and +; treats c1 and c2 as self-loops only), and -block-freq ignores the irreducible +; edge from c2 to c1. +; +; Below I use a CHECK-NEXT/NOT combo like an XFAIL with the granularity of a +; single check. If/when this behaviour is fixed, we'll know about it, and the +; test should be updated. +; +; CHECK-LABEL: Printing analysis {{.*}} for function 'crossloops': +; CHECK-NEXT: block-frequency-info: crossloops +define void @crossloops(i32 %a) { +; CHECK-NEXT: entry: float = 1.0, int = [[ENTRY:[0-9]+]] +entry: + %choose = call i32 @choose(i32 %a) + switch i32 %choose, label %exit [ i32 1, label %c1 + i32 2, label %c2 ], !prof !3 + +; This is like a single-line XFAIL (see above). +; CHECK-NEXT: c1: +; CHECK-NOT: float = 1.0, +c1: + %i1 = phi i32 [ %a, %entry ], [ %i1.inc, %c1 ], [ %i2.inc, %c2 ] + %i1.inc = add i32 %i1, 1 + %choose1 = call i32 @choose(i32 %i1) + switch i32 %choose1, label %exit [ i32 1, label %c1 + i32 2, label %c2 ], !prof !3 + +; This is like a single-line XFAIL (see above). +; CHECK-NEXT: c2: +; CHECK-NOT: float = 1.0, +c2: + %i2 = phi i32 [ %a, %entry ], [ %i1.inc, %c1 ], [ %i2.inc, %c2 ] + %i2.inc = add i32 %i2, 1 + %choose2 = call i32 @choose(i32 %i2) + switch i32 %choose2, label %exit [ i32 1, label %c1 + i32 2, label %c2 ], !prof !3 + +; We still shouldn't lose any frequency. +; CHECK-NEXT: exit: float = 1.0, int = [[ENTRY]] +exit: + ret void +} + +declare i32 @choose(i32) + +!2 = metadata !{metadata !"branch_weights", i32 3, i32 1} +!3 = metadata !{metadata !"branch_weights", i32 2, i32 2, i32 2} |