Make linear loop optimization safe from overflow

In the calcuation of `a * i + b`, `a` itself is calculated by doing:
    `(end - start) + (step - 1) / step`
(Note that we add `step - 1` as a way of doing `ceiling`).
This way of calculating `a` can overflow and produce the wrong result
if end and  start are in opposite sides of the spectrum.

We can force `a` to be a constant to guarantee that the right result
will be generated when doing loop optimization.

Bug: 231415860
Test: art/test/testrunner/testrunner.py --host --64 --optimizing -b
Change-Id: Ic056441f8d672b3c48cbbd2f3e4ebd7528e2c65b

1 files changed, 9 insertions, 0 deletions

diff --git a/compiler/optimizing/induction_var_range.h b/compiler/optimizing/induction_var_range.h
index 552837c044..6555bc2206 100644
--- a/compiler/optimizing/induction_var_range.h
+++ b/compiler/optimizing/induction_var_range.h
@@ -317,6 +317,15 @@ class InductionVarRange {
                                 /*out*/ bool* needs_finite_test,
                                 /*out*/ bool* needs_taken_test) const;
 
+  bool GenerateLastValueLinear(const HBasicBlock* context,
+                               const HLoopInformation* loop,
+                               HInductionVarAnalysis::InductionInfo* info,
+                               HInductionVarAnalysis::InductionInfo* trip,
+                               HGraph* graph,
+                               HBasicBlock* block,
+                               bool is_min,
+                               /*out*/ HInstruction** result) const;
+
   bool GenerateLastValuePolynomial(const HBasicBlock* context,
                                    const HLoopInformation* loop,
                                    HInductionVarAnalysis::InductionInfo* info,