[llvm] r233101 - [IRCE] Fix a regression introduced in r232444.

[Sanjoy Das]

Author: sanjoy
Date: Tue Mar 24 14:29:18 2015
New Revision: 233101

URL: http://llvm.org/viewvc/llvm-project?rev=233101&view=rev
Log:
[IRCE] Fix a regression introduced in r232444.

IRCE should not try to eliminate range checks that check an induction
variable against a loop-varying length.

Added:
    llvm/trunk/test/Transforms/IRCE/bug-loop-varying-upper-limit.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp?rev=233101&r1=233100&r2=233101&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp Tue Mar 24 14:29:18 2015
@@ -122,8 +122,9 @@ class InductiveRangeCheck {
   BranchInst *Branch;
   RangeCheckKind Kind;
 
-  static RangeCheckKind parseRangeCheckICmp(ICmpInst *ICI, ScalarEvolution &SE,
-                                            Value *&Index, Value *&Length);
+  static RangeCheckKind parseRangeCheckICmp(Loop *L, ICmpInst *ICI,
+                                            ScalarEvolution &SE, Value *&Index,
+                                            Value *&Length);
 
   static InductiveRangeCheck::RangeCheckKind
   parseRangeCheck(Loop *L, ScalarEvolution &SE, Value *Condition,
@@ -255,8 +256,18 @@ const char *InductiveRangeCheck::rangeCh
 /// RANGE_CHECK_UPPER.
 ///
 InductiveRangeCheck::RangeCheckKind
-InductiveRangeCheck::parseRangeCheckICmp(ICmpInst *ICI, ScalarEvolution &SE,
-                                         Value *&Index, Value *&Length) {
+InductiveRangeCheck::parseRangeCheckICmp(Loop *L, ICmpInst *ICI,
+                                         ScalarEvolution &SE, Value *&Index,
+                                         Value *&Length) {
+
+  auto IsNonNegativeAndNotLoopVarying = [&SE, L](Value *V) {
+    const SCEV *S = SE.getSCEV(V);
+    if (isa<SCEVCouldNotCompute>(S))
+      return false;
+
+    return SE.getLoopDisposition(S, L) == ScalarEvolution::LoopInvariant &&
+           SE.isKnownNonNegative(S);
+  };
 
   using namespace llvm::PatternMatch;
 
@@ -287,7 +298,7 @@ InductiveRangeCheck::parseRangeCheckICmp
       return RANGE_CHECK_LOWER;
     }
 
-    if (SE.isKnownNonNegative(SE.getSCEV(LHS))) {
+    if (IsNonNegativeAndNotLoopVarying(LHS)) {
       Index = RHS;
       Length = LHS;
       return RANGE_CHECK_UPPER;
@@ -298,7 +309,7 @@ InductiveRangeCheck::parseRangeCheckICmp
     std::swap(LHS, RHS);
   // fallthrough
   case ICmpInst::ICMP_UGT:
-    if (SE.isKnownNonNegative(SE.getSCEV(LHS))) {
+    if (IsNonNegativeAndNotLoopVarying(LHS)) {
       Index = RHS;
       Length = LHS;
       return RANGE_CHECK_BOTH;
@@ -328,8 +339,8 @@ InductiveRangeCheck::parseRangeCheck(Loo
     if (!ICmpA || !ICmpB)
       return InductiveRangeCheck::RANGE_CHECK_UNKNOWN;
 
-    auto RCKindA = parseRangeCheckICmp(ICmpA, SE, IndexA, LengthA);
-    auto RCKindB = parseRangeCheckICmp(ICmpB, SE, IndexB, LengthB);
+    auto RCKindA = parseRangeCheckICmp(L, ICmpA, SE, IndexA, LengthA);
+    auto RCKindB = parseRangeCheckICmp(L, ICmpB, SE, IndexB, LengthB);
 
     if (RCKindA == InductiveRangeCheck::RANGE_CHECK_UNKNOWN ||
         RCKindB == InductiveRangeCheck::RANGE_CHECK_UNKNOWN)
@@ -353,7 +364,7 @@ InductiveRangeCheck::parseRangeCheck(Loo
   if (ICmpInst *ICI = dyn_cast<ICmpInst>(Condition)) {
     Value *IndexVal = nullptr;
 
-    auto RCKind = parseRangeCheckICmp(ICI, SE, IndexVal, Length);
+    auto RCKind = parseRangeCheckICmp(L, ICI, SE, IndexVal, Length);
 
     if (RCKind == InductiveRangeCheck::RANGE_CHECK_UNKNOWN)
       return InductiveRangeCheck::RANGE_CHECK_UNKNOWN;

Added: llvm/trunk/test/Transforms/IRCE/bug-loop-varying-upper-limit.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IRCE/bug-loop-varying-upper-limit.ll?rev=233101&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/IRCE/bug-loop-varying-upper-limit.ll (added)
+++ llvm/trunk/test/Transforms/IRCE/bug-loop-varying-upper-limit.ll Tue Mar 24 14:29:18 2015
@@ -0,0 +1,31 @@
+; RUN: opt -irce-print-changed-loops -S -irce -verify < %s 2>&1 | FileCheck %s
+
+; CHECK-NOT: constrained loop
+
+define void @single_access_no_preloop_no_offset(i32 *%arr, i32 *%a_len_ptr, i32 %n) {
+ entry:
+  %first.itr.check = icmp sgt i32 %n, 0
+  br i1 %first.itr.check, label %loop, label %exit
+
+ loop:
+  %idx = phi i32 [ 0, %entry ] , [ %idx.next, %in.bounds ]
+  %idx.next = add i32 %idx, 1
+  %len = load i32, i32* %a_len_ptr, !range !0
+  %abc = icmp slt i32 %idx, %len
+  br i1 %abc, label %in.bounds, label %out.of.bounds, !prof !1
+
+ in.bounds:
+  %addr = getelementptr i32, i32* %arr, i32 %idx
+  store i32 0, i32* %addr
+  %next = icmp slt i32 %idx.next, %n
+  br i1 %next, label %loop, label %exit
+
+ out.of.bounds:
+  ret void
+
+ exit:
+  ret void
+}
+
+!0 = !{i32 0, i32 2147483647}
+!1 = !{!"branch_weights", i32 64, i32 4}