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llvm-project/llvm/test/Analysis/ScalarEvolution/trip-count-pow2.ll

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ScalarEvolution: Compute exit counts for loops with a power-of-2 step. If we have a loop of the form for (unsigned n = 0; n != (k & -32); n += 32) {} then we know that n is always divisible by 32 and the loop must terminate. Even if we have a condition where the loop counter will overflow it'll always hold this invariant. PR19183. Our loop vectorizer creates this pattern and it's also occasionally formed by loop counters derived from pointers. llvm-svn: 204728
2014-03-26 00:25:12 +08:00
; RUN: opt < %s -scalar-evolution -analyze | FileCheck %s
define void @test1(i32 %n) {
entry:
%s = mul i32 %n, 96
br label %loop
loop:
%i = phi i32 [ 0, %entry ], [ %i.next, %loop ]
%i.next = add i32 %i, 32
%t = icmp ne i32 %i.next, %s
br i1 %t, label %loop, label %exit
exit:
ret void
; CHECK-LABEL: @test1
; CHECK: Loop %loop: backedge-taken count is ((-32 + (96 * %n)) /u 32)
; CHECK: Loop %loop: max backedge-taken count is ((-32 + (96 * %n)) /u 32)
}
; PR19183
define i32 @test2(i32 %n) {
entry:
%s = and i32 %n, -32
br label %loop
loop:
%i = phi i32 [ 0, %entry ], [ %i.next, %loop ]
%i.next = add i32 %i, 32
%t = icmp ne i32 %i.next, %s
br i1 %t, label %loop, label %exit
exit:
ret i32 %i
; CHECK-LABEL: @test2
; CHECK: Loop %loop: backedge-taken count is ((-32 + (32 * (%n /u 32))) /u 32)
; CHECK: Loop %loop: max backedge-taken count is ((-32 + (32 * (%n /u 32))) /u 32)
}
define void @test3(i32 %n) {
entry:
%s = mul i32 %n, 96
br label %loop
loop:
%i = phi i32 [ 0, %entry ], [ %i.next, %loop ]
%i.next = add i32 %i, 96
%t = icmp ne i32 %i.next, %s
br i1 %t, label %loop, label %exit
exit:
ret void
; CHECK-LABEL: @test3
This patch de-pessimizes the calculation of loop trip counts in ScalarEvolution in the presence of multiple exits. Previously all loops exits had to have identical counts for a loop trip count to be considered computable. This pessimization was implemented by calling getBackedgeTakenCount(L) rather than getExitCount(L, ExitingBlock) inside of ScalarEvolution::getSmallConstantTripCount() (see the FIXME in the comments of that function). The pessimization was added to fix a corner case involving undefined behavior (pr/16130). This patch more precisely handles the undefined behavior case allowing the pessimization to be removed. ControlsExit replaces IsSubExpr to more precisely track the case where undefined behavior is expected to occur. Because undefined behavior is tracked more precisely we can remove MustExit from ExitLimit. MustExit was used to track the case where the limit was computed potentially assuming undefined behavior even if undefined behavior didn't necessarily occur. llvm-svn: 219517
2014-10-11 01:39:11 +08:00
; CHECK: Loop %loop: backedge-taken count is ((-96 + (96 * %n)) /u 96)
; CHECK: Loop %loop: max backedge-taken count is ((-96 + (96 * %n)) /u 96)
ScalarEvolution: Compute exit counts for loops with a power-of-2 step. If we have a loop of the form for (unsigned n = 0; n != (k & -32); n += 32) {} then we know that n is always divisible by 32 and the loop must terminate. Even if we have a condition where the loop counter will overflow it'll always hold this invariant. PR19183. Our loop vectorizer creates this pattern and it's also occasionally formed by loop counters derived from pointers. llvm-svn: 204728
2014-03-26 00:25:12 +08:00
}