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[IRCE] Temporarily disable unsigned latch conditions by default

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We have found some corner cases connected to range intersection where IRCE makes
a bad thing when the latch condition is unsigned. The fix for that will go as a follow up.
This patch temporarily disables IRCE for unsigned latch conditions until the issue is fixed.

The unsigned latch conditions were introduced to IRCE by rL310027.

Differential Revision: https://reviews.llvm.org/D38529

llvm-svn: 314881
This commit is contained in:
Max Kazantsev 2017-10-04 06:53:22 +00:00
parent 29c5a8da49
commit 01e8d2d5c4
7 changed files with 71 additions and 5 deletions
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21
lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
View File

@ -79,6 +79,9 @@ static cl::opt<int> MaxExitProbReciprocal("irce-max-exit-prob-reciprocal",
static cl::opt<bool> SkipProfitabilityChecks("irce-skip-profitability-checks",
cl::Hidden, cl::init(false));
static cl::opt<bool> AllowUnsignedLatchCondition("irce-allow-unsigned-latch",
cl::Hidden, cl::init(false));
static const char *ClonedLoopTag = "irce.loop.clone";
#define DEBUG_TYPE "irce"
@ -889,6 +892,15 @@ LoopStructure::parseLoopStructure(ScalarEvolution &SE,
IsSignedPredicate =
Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SGT;
// FIXME: We temporarily disable unsigned latch conditions by default
// because of found problems with intersecting signed and unsigned ranges.
// We are going to turn it on once the problems are fixed.
if (!IsSignedPredicate && !AllowUnsignedLatchCondition) {
FailureReason = "unsigned latch conditions are explicitly prohibited";
return None;
}
// The predicate that we need to check that the induction variable lies
// within bounds.
ICmpInst::Predicate BoundPred =
@ -964,6 +976,15 @@ LoopStructure::parseLoopStructure(ScalarEvolution &SE,
IsSignedPredicate =
Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SGT;
// FIXME: We temporarily disable unsigned latch conditions by default
// because of found problems with intersecting signed and unsigned ranges.
// We are going to turn it on once the problems are fixed.
if (!IsSignedPredicate && !AllowUnsignedLatchCondition) {
FailureReason = "unsigned latch conditions are explicitly prohibited";
return None;
}
// The predicate that we need to check that the induction variable lies
// within bounds.
ICmpInst::Predicate BoundPred =

2
test/Transforms/IRCE/clamp.ll
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@ -1,4 +1,4 @@
; RUN: opt -verify-loop-info -irce-print-changed-loops -irce -S < %s 2>&1 | FileCheck %s
; RUN: opt -verify-loop-info -irce-print-changed-loops -irce -irce-allow-unsigned-latch=true -S < %s 2>&1 | FileCheck %s
; The test demonstrates that incorrect behavior of Clamp may lead to incorrect
; calculation of post-loop exit condition.

2
test/Transforms/IRCE/eq_ne.ll
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@ -1,4 +1,4 @@
; RUN: opt -verify-loop-info -irce-print-changed-loops -irce -S < %s 2>&1 | FileCheck %s
; RUN: opt -verify-loop-info -irce-print-changed-loops -irce -irce-allow-unsigned-latch=true -S < %s 2>&1 | FileCheck %s
; CHECK: irce: in function test_01: constrained Loop at depth 1 containing: %loop<header><exiting>,%in.bounds<latch><exiting>
; CHECK: irce: in function test_01u: constrained Loop at depth 1 containing: %loop<header><exiting>,%in.bounds<latch><exiting>

45
test/Transforms/IRCE/range_intersect_miscompile.ll Normal file
View File

@ -0,0 +1,45 @@
; RUN: opt -irce -S < %s 2>&1 | FileCheck %s
; This test demonstrates a miscompile: the outer loop's IV iterates in range of
; [2, 400) and the range check is done against value 331. Due to a bug in range
; intersection IRCE manages to eliminate the range check without inserting a
; postloop, which is incorrect. So far IRCE is prohibited for this case.
define void @test_01() {
; CHECK-LABEL: test_01
; CHECK-NOT: br i1 true
entry:
br label %loop_header
loop_header: ; preds = %loop_latch, %entry
%iv = phi i32 [ 2, %entry ], [ %iv_next, %loop_latch ]
%iv.prev = phi i32 [ 1, %entry ], [ %iv, %loop_latch ]
%tmp2 = icmp sgt i32 %iv.prev, -1
br i1 %tmp2, label %loop_header.split.us, label %exit
loop_header.split.us: ; preds = %loop_header
br label %inner_loop
inner_loop: ; preds = %inner_loop, %loop_header.split.us
%inner_iv = phi i32 [ 1, %loop_header.split.us ], [ %inner_iv_next, %inner_loop ]
%inner_iv_next = add nuw nsw i32 %inner_iv, 1
%inner_cond = icmp ult i32 %inner_iv_next, 31
br i1 %inner_cond, label %inner_loop, label %range_check_block
exit: ; preds = %loop_latch, %loop_header
ret void
range_check_block: ; preds = %inner_loop
%range_check = icmp slt i32 %iv, 331
br i1 %range_check, label %loop_latch, label %deopt
loop_latch: ; preds = %range_check_block
%iv_next = add i32 %iv, 1
%loop_cond = icmp ult i32 %iv_next, 400
br i1 %loop_cond, label %loop_header, label %exit
deopt: ; preds = %range_check_block
ret void
}

2
test/Transforms/IRCE/stride_more_than_1.ll
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@ -1,4 +1,4 @@
; RUN: opt -verify-loop-info -irce-print-changed-loops -irce -S < %s 2>&1 | FileCheck %s
; RUN: opt -verify-loop-info -irce-print-changed-loops -irce -irce-allow-unsigned-latch=true -S < %s 2>&1 | FileCheck %s
; CHECK: irce: in function test_01: constrained Loop at depth 1 containing: %loop<header><exiting>,%in.bounds<latch><exiting>
; CHECK: irce: in function test_02: constrained Loop at depth 1 containing: %loop<header><exiting>,%in.bounds<latch><exiting>

2
test/Transforms/IRCE/unsigned_comparisons_ugt.ll
View File

@ -1,4 +1,4 @@
; RUN: opt -verify-loop-info -irce-print-changed-loops -irce -S < %s 2>&1 | FileCheck %s
; RUN: opt -verify-loop-info -irce-print-changed-loops -irce -irce-allow-unsigned-latch=true -S < %s 2>&1 | FileCheck %s
; CHECK: irce: in function test_01: constrained Loop at depth 1 containing: %loop<header><exiting>,%in.bounds<latch><exiting>
; CHECK: irce: in function test_02: constrained Loop at depth 1 containing: %loop<header><exiting>,%in.bounds<latch><exiting>

2
test/Transforms/IRCE/unsigned_comparisons_ult.ll
View File

@ -1,4 +1,4 @@
; RUN: opt -verify-loop-info -irce-print-changed-loops -irce -S < %s 2>&1 | FileCheck %s
; RUN: opt -verify-loop-info -irce-print-changed-loops -irce -irce-allow-unsigned-latch=true -S < %s 2>&1 | FileCheck %s
; CHECK: irce: in function test_01: constrained Loop at depth 1 containing: %loop<header><exiting>,%in.bounds<latch><exiting>
; CHECK: irce: in function test_02: constrained Loop at depth 1 containing: %loop<header><exiting>,%in.bounds<latch><exiting>