[Guards] Introduce loop-predication pass
This patch introduces guard based loop predication optimization. The new LoopPredication pass tries to convert loop variant range checks to loop invariant by widening checks across loop iterations. For example, it will convert
for (i = 0; i < n; i++) {
guard(i < len);
...
}
to
for (i = 0; i < n; i++) {
guard(n - 1 < len);
...
}
After this transformation the condition of the guard is loop invariant, so loop-unswitch can later unswitch the loop by this condition which basically predicates the loop by the widened condition:
if (n - 1 < len)
for (i = 0; i < n; i++) {
...
}
else
deoptimize
This patch relies on an NFC change to make ScalarEvolution::isMonotonicPredicate public (revision 293062).
Reviewed By: sanjoy
Differential Revision: https://reviews.llvm.org/D29034
llvm-svn: 293064
diff --git a/llvm/test/Transforms/LoopPredication/visited.ll b/llvm/test/Transforms/LoopPredication/visited.ll
new file mode 100644
index 0000000..e9aae77
--- /dev/null
+++ b/llvm/test/Transforms/LoopPredication/visited.ll
@@ -0,0 +1,140 @@
+; RUN: opt -S -loop-predication < %s 2>&1 | FileCheck %s
+; RUN: opt -S -passes='require<scalar-evolution>,loop(loop-predication)' < %s 2>&1 | FileCheck %s
+
+declare void @llvm.experimental.guard(i1, ...)
+
+define i32 @test_visited(i32* %array, i32 %length, i32 %n, i32 %x) {
+; CHECK-LABEL: @test_visited
+entry:
+ %tmp5 = icmp eq i32 %n, 0
+ br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK: [[iteration_count:[^ ]+]] = add i32 %n, -1
+; CHECK-NEXT: [[wide_cond:[^ ]+]] = icmp ult i32 [[iteration_count]], %length
+; CHECK-NEXT: br label %loop
+ br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: %unrelated.cond = icmp eq i32 %x, %i
+; CHECK: [[guard_cond:[^ ]+]] = and i1 %unrelated.cond, [[wide_cond]]
+; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 [[guard_cond]], i32 9) [ "deopt"() ]
+ %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+ %i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
+ %within.bounds = icmp ult i32 %i, %length
+ %unrelated.cond = icmp eq i32 %x, %i
+ %guard.cond.2 = and i1 %within.bounds, %unrelated.cond
+ %guard.cond.3 = and i1 %guard.cond.2, %unrelated.cond
+ %guard.cond.4 = and i1 %guard.cond.3, %guard.cond.2
+ %guard.cond.5 = and i1 %guard.cond.4, %guard.cond.3
+ %guard.cond.6 = and i1 %guard.cond.5, %guard.cond.4
+ %guard.cond.7 = and i1 %guard.cond.6, %guard.cond.5
+ %guard.cond.8 = and i1 %guard.cond.7, %guard.cond.6
+ %guard.cond.9 = and i1 %guard.cond.8, %guard.cond.7
+ %guard.cond.10 = and i1 %guard.cond.9, %guard.cond.8
+ %guard.cond.11 = and i1 %guard.cond.10, %guard.cond.9
+ %guard.cond.12 = and i1 %guard.cond.11, %guard.cond.10
+ %guard.cond.13 = and i1 %guard.cond.12, %guard.cond.11
+ %guard.cond.14 = and i1 %guard.cond.13, %guard.cond.12
+ %guard.cond.15 = and i1 %guard.cond.14, %guard.cond.13
+ %guard.cond.16 = and i1 %guard.cond.15, %guard.cond.14
+ %guard.cond.17 = and i1 %guard.cond.16, %guard.cond.15
+ %guard.cond.18 = and i1 %guard.cond.17, %guard.cond.16
+ %guard.cond.19 = and i1 %guard.cond.18, %guard.cond.17
+ %guard.cond.20 = and i1 %guard.cond.19, %guard.cond.18
+ %guard.cond.21 = and i1 %guard.cond.20, %guard.cond.19
+ %guard.cond.22 = and i1 %guard.cond.21, %guard.cond.20
+ %guard.cond.23 = and i1 %guard.cond.22, %guard.cond.21
+ %guard.cond.24 = and i1 %guard.cond.23, %guard.cond.22
+ %guard.cond.25 = and i1 %guard.cond.24, %guard.cond.23
+ %guard.cond.26 = and i1 %guard.cond.25, %guard.cond.24
+ %guard.cond.27 = and i1 %guard.cond.26, %guard.cond.25
+ %guard.cond.28 = and i1 %guard.cond.27, %guard.cond.26
+ %guard.cond.29 = and i1 %guard.cond.28, %guard.cond.27
+ %guard.cond.30 = and i1 %guard.cond.29, %guard.cond.28
+ %guard.cond.31 = and i1 %guard.cond.30, %guard.cond.29
+ %guard.cond.32 = and i1 %guard.cond.31, %guard.cond.30
+ %guard.cond.33 = and i1 %guard.cond.32, %guard.cond.31
+ %guard.cond.34 = and i1 %guard.cond.33, %guard.cond.32
+ %guard.cond.35 = and i1 %guard.cond.34, %guard.cond.33
+ %guard.cond.36 = and i1 %guard.cond.35, %guard.cond.34
+ %guard.cond.37 = and i1 %guard.cond.36, %guard.cond.35
+ %guard.cond.38 = and i1 %guard.cond.37, %guard.cond.36
+ %guard.cond.39 = and i1 %guard.cond.38, %guard.cond.37
+ %guard.cond.40 = and i1 %guard.cond.39, %guard.cond.38
+ %guard.cond.41 = and i1 %guard.cond.40, %guard.cond.39
+ %guard.cond.42 = and i1 %guard.cond.41, %guard.cond.40
+ %guard.cond.43 = and i1 %guard.cond.42, %guard.cond.41
+ %guard.cond.44 = and i1 %guard.cond.43, %guard.cond.42
+ %guard.cond.45 = and i1 %guard.cond.44, %guard.cond.43
+ %guard.cond.46 = and i1 %guard.cond.45, %guard.cond.44
+ %guard.cond.47 = and i1 %guard.cond.46, %guard.cond.45
+ %guard.cond.48 = and i1 %guard.cond.47, %guard.cond.46
+ %guard.cond.49 = and i1 %guard.cond.48, %guard.cond.47
+ %guard.cond.50 = and i1 %guard.cond.49, %guard.cond.48
+ %guard.cond.51 = and i1 %guard.cond.50, %guard.cond.49
+ %guard.cond.52 = and i1 %guard.cond.51, %guard.cond.50
+ %guard.cond.53 = and i1 %guard.cond.52, %guard.cond.51
+ %guard.cond.54 = and i1 %guard.cond.53, %guard.cond.52
+ %guard.cond.55 = and i1 %guard.cond.54, %guard.cond.53
+ %guard.cond.56 = and i1 %guard.cond.55, %guard.cond.54
+ %guard.cond.57 = and i1 %guard.cond.56, %guard.cond.55
+ %guard.cond.58 = and i1 %guard.cond.57, %guard.cond.56
+ %guard.cond.59 = and i1 %guard.cond.58, %guard.cond.57
+ %guard.cond.60 = and i1 %guard.cond.59, %guard.cond.58
+ %guard.cond.61 = and i1 %guard.cond.60, %guard.cond.59
+ %guard.cond.62 = and i1 %guard.cond.61, %guard.cond.60
+ %guard.cond.63 = and i1 %guard.cond.62, %guard.cond.61
+ %guard.cond.64 = and i1 %guard.cond.63, %guard.cond.62
+ %guard.cond.65 = and i1 %guard.cond.64, %guard.cond.63
+ %guard.cond.66 = and i1 %guard.cond.65, %guard.cond.64
+ %guard.cond.67 = and i1 %guard.cond.66, %guard.cond.65
+ %guard.cond.68 = and i1 %guard.cond.67, %guard.cond.66
+ %guard.cond.69 = and i1 %guard.cond.68, %guard.cond.67
+ %guard.cond.70 = and i1 %guard.cond.69, %guard.cond.68
+ %guard.cond.71 = and i1 %guard.cond.70, %guard.cond.69
+ %guard.cond.72 = and i1 %guard.cond.71, %guard.cond.70
+ %guard.cond.73 = and i1 %guard.cond.72, %guard.cond.71
+ %guard.cond.74 = and i1 %guard.cond.73, %guard.cond.72
+ %guard.cond.75 = and i1 %guard.cond.74, %guard.cond.73
+ %guard.cond.76 = and i1 %guard.cond.75, %guard.cond.74
+ %guard.cond.77 = and i1 %guard.cond.76, %guard.cond.75
+ %guard.cond.78 = and i1 %guard.cond.77, %guard.cond.76
+ %guard.cond.79 = and i1 %guard.cond.78, %guard.cond.77
+ %guard.cond.80 = and i1 %guard.cond.79, %guard.cond.78
+ %guard.cond.81 = and i1 %guard.cond.80, %guard.cond.79
+ %guard.cond.82 = and i1 %guard.cond.81, %guard.cond.80
+ %guard.cond.83 = and i1 %guard.cond.82, %guard.cond.81
+ %guard.cond.84 = and i1 %guard.cond.83, %guard.cond.82
+ %guard.cond.85 = and i1 %guard.cond.84, %guard.cond.83
+ %guard.cond.86 = and i1 %guard.cond.85, %guard.cond.84
+ %guard.cond.87 = and i1 %guard.cond.86, %guard.cond.85
+ %guard.cond.88 = and i1 %guard.cond.87, %guard.cond.86
+ %guard.cond.89 = and i1 %guard.cond.88, %guard.cond.87
+ %guard.cond.90 = and i1 %guard.cond.89, %guard.cond.88
+ %guard.cond.91 = and i1 %guard.cond.90, %guard.cond.89
+ %guard.cond.92 = and i1 %guard.cond.91, %guard.cond.90
+ %guard.cond.93 = and i1 %guard.cond.92, %guard.cond.91
+ %guard.cond.94 = and i1 %guard.cond.93, %guard.cond.92
+ %guard.cond.95 = and i1 %guard.cond.94, %guard.cond.93
+ %guard.cond.96 = and i1 %guard.cond.95, %guard.cond.94
+ %guard.cond.97 = and i1 %guard.cond.96, %guard.cond.95
+ %guard.cond.98 = and i1 %guard.cond.97, %guard.cond.96
+ %guard.cond.99 = and i1 %guard.cond.98, %guard.cond.97
+ call void (i1, ...) @llvm.experimental.guard(i1 %guard.cond.99, i32 9) [ "deopt"() ]
+
+ %i.i64 = zext i32 %i to i64
+ %array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
+ %array.i = load i32, i32* %array.i.ptr, align 4
+ %loop.acc.next = add i32 %loop.acc, %array.i
+
+ %i.next = add nuw i32 %i, 1
+ %continue = icmp ult i32 %i.next, %n
+ br i1 %continue, label %loop, label %exit
+
+exit:
+ %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+ ret i32 %result
+}
\ No newline at end of file