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llvm-6502/test/Transforms/IRCE/single-access-with-preloop.ll

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Add a new pass "inductive range check elimination" IRCE eliminates range checks of the form 0 <= A * I + B < Length by splitting a loop's iteration space into three segments in a way that the check is completely redundant in the middle segment. As an example, IRCE will convert len = < known positive > for (i = 0; i < n; i++) { if (0 <= i && i < len) { do_something(); } else { throw_out_of_bounds(); } } to len = < known positive > limit = smin(n, len) // no first segment for (i = 0; i < limit; i++) { if (0 <= i && i < len) { // this check is fully redundant do_something(); } else { throw_out_of_bounds(); } } for (i = limit; i < n; i++) { if (0 <= i && i < len) { do_something(); } else { throw_out_of_bounds(); } } IRCE can deal with multiple range checks in the same loop (it takes the intersection of the ranges that will make each of them redundant individually). Currently IRCE does not do any profitability analysis. That is a TODO. Please note that the status of this pass is *experimental*, and it is not part of any default pass pipeline. Having said that, I will love to get feedback and general input from people interested in trying this out. This pass was originally r226201. It was reverted because it used C++ features not supported by MSVC 2012. Differential Revision: http://reviews.llvm.org/D6693 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226238 91177308-0d34-0410-b5e6-96231b3b80d8
2015-01-16 01:03:22 +00:00
; RUN: opt -irce -S < %s | FileCheck %s
define void @single_access_with_preloop(i32 *%arr, i32 *%a_len_ptr, i32 %n, i32 %offset) {
entry:
%len = load i32* %a_len_ptr, !range !0
%first.itr.check = icmp sgt i32 %n, 0
br i1 %first.itr.check, label %loop, label %exit
loop:
%idx = phi i32 [ 0, %entry ] , [ %idx.next, %in.bounds ]
%idx.next = add i32 %idx, 1
%array.idx = add i32 %idx, %offset
%abc.high = icmp slt i32 %array.idx, %len
%abc.low = icmp sge i32 %array.idx, 0
%abc = and i1 %abc.low, %abc.high
Teach IRCE to look at branch weights when recognizing range checks Splitting a loop to make range checks redundant is profitable only if the range check "never" fails. Make this fact a part of recognizing a range check -- a branch is a range check only if it is expected to pass (via branch_weights metadata). Differential Revision: http://reviews.llvm.org/D7192 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227249 91177308-0d34-0410-b5e6-96231b3b80d8
2015-01-27 21:38:12 +00:00
br i1 %abc, label %in.bounds, label %out.of.bounds, !prof !1
Add a new pass "inductive range check elimination" IRCE eliminates range checks of the form 0 <= A * I + B < Length by splitting a loop's iteration space into three segments in a way that the check is completely redundant in the middle segment. As an example, IRCE will convert len = < known positive > for (i = 0; i < n; i++) { if (0 <= i && i < len) { do_something(); } else { throw_out_of_bounds(); } } to len = < known positive > limit = smin(n, len) // no first segment for (i = 0; i < limit; i++) { if (0 <= i && i < len) { // this check is fully redundant do_something(); } else { throw_out_of_bounds(); } } for (i = limit; i < n; i++) { if (0 <= i && i < len) { do_something(); } else { throw_out_of_bounds(); } } IRCE can deal with multiple range checks in the same loop (it takes the intersection of the ranges that will make each of them redundant individually). Currently IRCE does not do any profitability analysis. That is a TODO. Please note that the status of this pass is *experimental*, and it is not part of any default pass pipeline. Having said that, I will love to get feedback and general input from people interested in trying this out. This pass was originally r226201. It was reverted because it used C++ features not supported by MSVC 2012. Differential Revision: http://reviews.llvm.org/D6693 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226238 91177308-0d34-0410-b5e6-96231b3b80d8
2015-01-16 01:03:22 +00:00
in.bounds:
%addr = getelementptr i32* %arr, i32 %array.idx
store i32 0, i32* %addr
%next = icmp slt i32 %idx.next, %n
br i1 %next, label %loop, label %exit
out.of.bounds:
ret void
exit:
ret void
}
; CHECK-LABEL: loop.preheader:
; CHECK: [[safe_start:[^ ]+]] = sub i32 0, %offset
; CHECK: [[safe_end:[^ ]+]] = sub i32 %len, %offset
; CHECK: [[exit_preloop_at_cond:[^ ]+]] = icmp slt i32 %n, [[safe_start]]
; CHECK: [[exit_preloop_at:[^ ]+]] = select i1 [[exit_preloop_at_cond]], i32 %n, i32 [[safe_start]]
; CHECK: [[exit_mainloop_at_cond:[^ ]+]] = icmp slt i32 %n, [[safe_end]]
; CHECK: [[exit_mainloop_at:[^ ]+]] = select i1 [[exit_mainloop_at_cond]], i32 %n, i32 [[safe_end]]
; CHECK-LABEL: in.bounds:
; CHECK: [[continue_mainloop_cond:[^ ]+]] = icmp slt i32 %idx.next, [[exit_mainloop_at]]
; CHECK: br i1 [[continue_mainloop_cond]], label %loop, label %main.exit.selector
; CHECK-LABEL: main.exit.selector:
; CHECK: [[mainloop_its_left:[^ ]+]] = icmp slt i32 %idx.next, %n
; CHECK: br i1 [[mainloop_its_left]], label %main.pseudo.exit, label %exit.loopexit
; CHECK-LABEL: in.bounds.preloop:
; CHECK: [[continue_preloop_cond:[^ ]+]] = icmp slt i32 %idx.next.preloop, [[exit_preloop_at]]
; CHECK: br i1 [[continue_preloop_cond]], label %loop.preloop, label %preloop.exit.selector
; CHECK-LABEL: preloop.exit.selector:
; CHECK: [[preloop_its_left:[^ ]+]] = icmp slt i32 %idx.next.preloop, %n
; CHECK: br i1 [[preloop_its_left]], label %preloop.pseudo.exit, label %exit.loopexit
; CHECK-LABEL: in.bounds.postloop:
; CHECK: %next.postloop = icmp slt i32 %idx.next.postloop, %n
; CHECK: br i1 %next.postloop, label %loop.postloop, label %exit.loopexit
!0 = !{i32 0, i32 2147483647}
Teach IRCE to look at branch weights when recognizing range checks Splitting a loop to make range checks redundant is profitable only if the range check "never" fails. Make this fact a part of recognizing a range check -- a branch is a range check only if it is expected to pass (via branch_weights metadata). Differential Revision: http://reviews.llvm.org/D7192 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227249 91177308-0d34-0410-b5e6-96231b3b80d8
2015-01-27 21:38:12 +00:00
!1 = !{!"branch_weights", i32 64, i32 4}
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