Merge pull request swiftlang#5622 from shajrawi/array_bouds_check_false

[SILOptimizer] add support for always false comparisons to ArrayBoundsCheckOpts

Author: Joe Shajrawi

lib/SILOptimizer/LoopTransforms/ArrayBoundsCheckOpts.cpp

@@ -1097,6 +1097,38 @@ static bool isComparisonKnownTrue(BuiltinInst *Builtin, InductionInfo &IndVar) {
                                     m_Specific(IndVar.End)));
 }
 
+/// Based on the induction variable information this comparison is known to be
+/// false.
+static bool isComparisonKnownFalse(BuiltinInst *Builtin,
+                                   InductionInfo &IndVar) {
+  if (!IndVar.IsOverflowCheckInserted ||
+      IndVar.Cmp != BuiltinValueKind::ICMP_EQ)
+    return false;
+
+  // Pattern match a false condition patterns that we can detect and optimize:
+  // Iteration count < 0 (start)
+  // Iteration count + 1 <= 0 (start)
+  // Iteration count + 1 < 0 (start)
+  // Iteration count + 1 == 0 (start)
+  auto MatchIndVarHeader = m_Specific(IndVar.HeaderVal);
+  auto MatchIncrementIndVar = m_TupleExtractInst(
+      m_ApplyInst(BuiltinValueKind::SAddOver, MatchIndVarHeader, m_One()), 0);
+  auto MatchIndVarStart = m_Specific(IndVar.Start);
+
+  if (match(Builtin,
+            m_ApplyInst(BuiltinValueKind::ICMP_SLT,
+                        m_CombineOr(MatchIndVarHeader, MatchIncrementIndVar),
+                        MatchIndVarStart)) ||
+      match(Builtin, m_ApplyInst(BuiltinValueKind::ICMP_EQ,
+                                 MatchIncrementIndVar, MatchIndVarStart)) ||
+      match(Builtin, m_ApplyInst(BuiltinValueKind::ICMP_SLE,
+                                 MatchIncrementIndVar, MatchIndVarStart))) {
+    return true;
+  }
+
+  return false;
+}
+
 /// Analyse the loop for arrays that are not modified and perform dominator tree
 /// based redundant bounds check removal.
 static bool hoistBoundsChecks(SILLoop *Loop, DominanceInfo *DT, SILLoopInfo *LI,
@@ -1200,6 +1232,15 @@ static bool hoistBoundsChecks(SILLoop *Loop, DominanceInfo *DT, SILLoopInfo *LI,
               Changed = true;
               continue;
             }
+            if (isComparisonKnownFalse(Builtin, *IV)) {
+              if (!FalseVal) {
+                FalseVal = SILValue(B.createIntegerLiteral(
+                    Builtin->getLoc(), Builtin->getType(), 0));
+              }
+              Builtin->replaceAllUsesWith(FalseVal);
+              Changed = true;
+              continue;
+            }
             // Check whether a dominating check of the condition let's us
             // replace
             // the condition by false.

test/SILOptimizer/abcopts.sil

@@ -441,6 +441,67 @@ bb3:
   return %23 : $Int32
 }
 
+// HOIST-LABEL: sil @always_false_hoist
+// HOIST: bb4
+// HOIST:   builtin "sadd_with_overflow_Int32"
+// HOIST:   tuple_extract
+// HOIST-NOT: builtin "cmp_slt_Int32"
+// HOIST-NOT: builtin "cmp_sle_Int32"
+// HOIST-NOT: builtin "cmp_eq_Int32"
+// HOIST:   cond_fail
+// HOIST:   cond_fail
+// HOIST:   cond_fail
+// HOIST:   cond_fail
+// HOIST:   builtin "cmp_eq_Int32"
+// HOIST:   cond_br
+// HOIST: }
+sil @always_false_hoist : $@convention(thin) (@owned Array<Int>) -> () {
+bb0(%0 : $Array<Int>):
+  %z0 = integer_literal $Builtin.Int32, 0
+  %f1 = function_ref @getCount2 : $@convention(method) (@owned Array<Int>) -> Int32
+  retain_value %0 : $Array<Int>
+  %t1 = apply %f1(%0) : $@convention(method) (@owned Array<Int>) -> Int32
+  %c1 = struct_extract %t1 : $Int32, #Int32._value
+  %t2 = builtin "cmp_eq_Int32"(%z0 : $Builtin.Int32, %c1 : $Builtin.Int32) : $Builtin.Int1
+  cond_br %t2, bb5, bb1
+
+bb1:
+  br bb2(%z0 : $Builtin.Int32)
+
+bb2(%i0 : $Builtin.Int32):
+  cond_br undef, bb3, bb4
+
+bb3:
+  %f2 = function_ref @checkbounds2 : $@convention(method) (Int32, Bool, @owned Array<Int>) -> _DependenceToken
+  retain_value %0 : $Array<Int>
+  %t3 = struct $Int32(%i0 : $Builtin.Int32)
+
+  br bb4
+
+bb4:
+  %t5 = integer_literal $Builtin.Int1, 0
+  %i2 = integer_literal $Builtin.Int32, 1
+  %t6 = builtin "sadd_with_overflow_Int32"(%i0 : $Builtin.Int32, %i2 : $Builtin.Int32, %t5 : $Builtin.Int1) : $(Builtin.Int32, Builtin.Int1)
+  %t7 = tuple_extract %t6 : $(Builtin.Int32, Builtin.Int1), 0
+  %t8 = tuple_extract %t6 : $(Builtin.Int32, Builtin.Int1), 1
+  cond_fail %t8 : $Builtin.Int1
+  %af1 = builtin "cmp_slt_Int32"(%i0 : $Builtin.Int32, %z0 : $Builtin.Int32) : $Builtin.Int1
+  cond_fail %af1 : $Builtin.Int1
+  %af2 = builtin "cmp_slt_Int32"(%t7 : $Builtin.Int32, %z0 : $Builtin.Int32) : $Builtin.Int1
+  cond_fail %af2 : $Builtin.Int1
+  %af3 = builtin "cmp_sle_Int32"(%t7 : $Builtin.Int32, %z0 : $Builtin.Int32) : $Builtin.Int1
+  cond_fail %af3 : $Builtin.Int1
+  %af4 = builtin "cmp_eq_Int32"(%t7 : $Builtin.Int32, %z0 : $Builtin.Int32) : $Builtin.Int1
+  cond_fail %af4 : $Builtin.Int1
+  %8 = builtin "cmp_eq_Int32"(%t7 : $Builtin.Int32, %c1 : $Builtin.Int32) : $Builtin.Int1
+  cond_br %8, bb5, bb2(%t7 : $Builtin.Int32)
+
+bb5:
+  %r1 = tuple ()
+  return %r1 : $()
+}
+
+
 // HOIST-LABEL: sil @hoistinvariant
 
 // Preheader.