[PATCH] D59211: [LSR] Check for signed overflow in NarrowSearchSpaceByDetectingSupersets.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: qcolombet, gilr, kparzysz.
Herald added subscribers: jdoerfert, hiraditya.
Herald added a project: LLVM.

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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D59211

Files:
  llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
  llvm/test/Transforms/LoopStrengthReduce/X86/lsr-overflow.ll


Index: llvm/test/Transforms/LoopStrengthReduce/X86/lsr-overflow.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/LoopStrengthReduce/X86/lsr-overflow.ll
@@ -0,0 +1,22 @@
+; 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"
+
+; CHECK: overflow1
+define void @overflow1(i64 %a) {
+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
+}
Index: llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -74,7 +74,6 @@
 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
 #include "llvm/Analysis/ScalarEvolutionNormalization.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
-#include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Constant.h"
@@ -99,6 +98,7 @@
 #include "llvm/IR/ValueHandle.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/Casting.h"
+#include "llvm/Support/CheckedArithmetic.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Debug.h"
@@ -108,6 +108,7 @@
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/Local.h"
 #include <algorithm>
 #include <cassert>
 #include <cstddef>
@@ -115,8 +116,8 @@
 #include <cstdlib>
 #include <iterator>
 #include <limits>
-#include <numeric>
 #include <map>
+#include <numeric>
 #include <utility>
 
 using namespace llvm;
@@ -4435,7 +4436,14 @@
              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();
+
+            Optional<int64_t> MaybeResult =
+                checkedAdd(NewF.BaseOffset, C->getValue()->getSExtValue());
+            // Skip simplification if addition overflows.
+            if (!MaybeResult)
+              continue;
+
+            NewF.BaseOffset = *MaybeResult;
             NewF.BaseRegs.erase(NewF.BaseRegs.begin() +
                                 (I - F.BaseRegs.begin()));
             if (LU.HasFormulaWithSameRegs(NewF)) {


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