[llvm] r356256 - [LSR] Check for signed overflow in NarrowSearchSpaceByDetectingSupersets.

[Florian Hahn via llvm-commits]

Author: fhahn
Date: Fri Mar 15 05:17:36 2019
New Revision: 356256

URL: http://llvm.org/viewvc/llvm-project?rev=356256&view=rev
Log:
[LSR] Check for signed overflow in NarrowSearchSpaceByDetectingSupersets.

We are adding a sign extended IR value to an int64_t, which can cause
signed overflows, as in the attached test case, where we have a formula
with BaseOffset = -1 and a constant with numeric_limits<int64_t>::min().

If the addition would overflow, skip the simplification for this
formula. Note that the target triple is required to trigger the failure.

Reviewers: qcolombet, gilr, kparzysz, efriedma

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D59211

Added:
    llvm/trunk/test/Transforms/LoopStrengthReduce/X86/lsr-overflow.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp?rev=356256&r1=356255&r2=356256&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp Fri Mar 15 05:17:36 2019
@@ -4423,7 +4423,9 @@ void LSRInstance::NarrowSearchSpaceByDet
              I = F.BaseRegs.begin(), E = F.BaseRegs.end(); I != E; ++I) {
           if (const SCEVConstant *C = dyn_cast<SCEVConstant>(*I)) {
             Formula NewF = F;
-            NewF.BaseOffset += C->getValue()->getSExtValue();
+            //FIXME: Formulas should store bitwidth to do wrapping properly.
+            //       See PR41034.
+            NewF.BaseOffset += (uint64_t)C->getValue()->getSExtValue();
             NewF.BaseRegs.erase(NewF.BaseRegs.begin() +
                                 (I - F.BaseRegs.begin()));
             if (LU.HasFormulaWithSameRegs(NewF)) {

Added: llvm/trunk/test/Transforms/LoopStrengthReduce/X86/lsr-overflow.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopStrengthReduce/X86/lsr-overflow.ll?rev=356256&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/LoopStrengthReduce/X86/lsr-overflow.ll (added)
+++ llvm/trunk/test/Transforms/LoopStrengthReduce/X86/lsr-overflow.ll Fri Mar 15 05:17:36 2019
@@ -0,0 +1,38 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -lsr-complexity-limit=50 -loop-reduce -S %s | FileCheck %s
+
+target triple = "x86_64-apple-macosx10.14.0"
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+
+define void @overflow1(i64 %a) {
+; CHECK-LABEL: @overflow1(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    br label [[BB1:%.*]]
+; CHECK:       bb1:
+; CHECK-NEXT:    [[TMP:%.*]] = phi i64 [ [[A:%.*]], [[BB:%.*]] ], [ [[TMP6:%.*]], [[BB1]] ]
+; CHECK-NEXT:    [[TMP0:%.*]] = add i64 [[TMP]], -9223372036854775808
+; CHECK-NEXT:    [[TMP4:%.*]] = icmp ne i64 [[TMP0]], 0
+; CHECK-NEXT:    [[TMP5:%.*]] = and i1 [[TMP4]], true
+; CHECK-NEXT:    [[TMP6]] = add i64 [[TMP]], 1
+; CHECK-NEXT:    br i1 [[TMP5]], label [[BB1]], label [[BB7:%.*]]
+; CHECK:       bb7:
+; CHECK-NEXT:    [[TMP1:%.*]] = add i64 [[TMP6]], -1
+; CHECK-NEXT:    [[TMP9:%.*]] = and i64 [[TMP1]], 1
+; CHECK-NEXT:    [[TMP10:%.*]] = icmp eq i64 [[TMP9]], 0
+; CHECK-NEXT:    unreachable
+;
+bb:
+  br label %bb1
+
+bb1:                                              ; preds = %bb1, %bb
+  %tmp = phi i64 [ %a, %bb ], [ %tmp6, %bb1 ]
+  %tmp4 = icmp ne i64 %tmp, -9223372036854775808
+  %tmp5 = and i1 %tmp4, 1
+  %tmp6 = add i64 %tmp, 1
+  br i1 %tmp5, label %bb1, label %bb7
+
+bb7:                                              ; preds = %bb1
+  %tmp9 = and i64 %tmp, 1
+  %tmp10 = icmp eq i64 %tmp9, 0
+  unreachable
+}