[IRCE] Temporarily disable unsigned latch conditions by default

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

7 files changed, 71 insertions, 5 deletions

diff --git a/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp b/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
index ce318f7d1de..cc0f2c5bb48 100644
--- a/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
@@ -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 =
diff --git a/llvm/test/Transforms/IRCE/clamp.ll b/llvm/test/Transforms/IRCE/clamp.ll
index dbbd336eb2e..c005b0504b3 100644
--- a/llvm/test/Transforms/IRCE/clamp.ll
+++ b/llvm/test/Transforms/IRCE/clamp.ll
@@ -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.
diff --git a/llvm/test/Transforms/IRCE/eq_ne.ll b/llvm/test/Transforms/IRCE/eq_ne.ll
index 7fbed3be0f1..6f63f4cf271 100644
--- a/llvm/test/Transforms/IRCE/eq_ne.ll
+++ b/llvm/test/Transforms/IRCE/eq_ne.ll
@@ -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>
diff --git a/llvm/test/Transforms/IRCE/range_intersect_miscompile.ll b/llvm/test/Transforms/IRCE/range_intersect_miscompile.ll
new file mode 100644
index 00000000000..3a93ad1f396
--- /dev/null
+++ b/llvm/test/Transforms/IRCE/range_intersect_miscompile.ll
@@ -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
+}
diff --git a/llvm/test/Transforms/IRCE/stride_more_than_1.ll b/llvm/test/Transforms/IRCE/stride_more_than_1.ll
index 0918aeb8402..de13a648a51 100644
--- a/llvm/test/Transforms/IRCE/stride_more_than_1.ll
+++ b/llvm/test/Transforms/IRCE/stride_more_than_1.ll
@@ -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>
diff --git a/llvm/test/Transforms/IRCE/unsigned_comparisons_ugt.ll b/llvm/test/Transforms/IRCE/unsigned_comparisons_ugt.ll
index 183706a2e6c..72a56ff17af 100644
--- a/llvm/test/Transforms/IRCE/unsigned_comparisons_ugt.ll
+++ b/llvm/test/Transforms/IRCE/unsigned_comparisons_ugt.ll
@@ -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>
diff --git a/llvm/test/Transforms/IRCE/unsigned_comparisons_ult.ll b/llvm/test/Transforms/IRCE/unsigned_comparisons_ult.ll
index 155b27bb635..34765572e5f 100644
--- a/llvm/test/Transforms/IRCE/unsigned_comparisons_ult.ll
+++ b/llvm/test/Transforms/IRCE/unsigned_comparisons_ult.ll
@@ -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>