[PATCH] D18777: [ValueTracking] An improvement to IR ValueTracking on Non-negative Integers

[Li Huang via llvm-commits]

lihuang edited reviewers, added: apilipenko; removed: mbodart.
lihuang removed rL LLVM as the repository for this revision.
lihuang updated this revision to Diff 73080.
lihuang added a comment.

Rebase this patch to latest source.

As the performance problem has been fixed by r282650 (https://reviews.llvm.org/D24280), we can re-commit this patch.


https://reviews.llvm.org/D18777

Files:
  lib/Analysis/ValueTracking.cpp
  test/Transforms/BBVectorize/loop1.ll


Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -1300,9 +1300,43 @@
           APInt KnownZero3(KnownZero), KnownOne3(KnownOne);
           computeKnownBits(L, KnownZero3, KnownOne3, Depth + 1, Q);
 
-          KnownZero = APInt::getLowBitsSet(BitWidth,
-                                           std::min(KnownZero2.countTrailingOnes(),
-                                                    KnownZero3.countTrailingOnes()));
+          KnownZero = APInt::getLowBitsSet(
+              BitWidth, std::min(KnownZero2.countTrailingOnes(),
+                                 KnownZero3.countTrailingOnes()));
+
+          auto *OverflowOp = dyn_cast<OverflowingBinaryOperator>(LU);
+          if (OverflowOp && OverflowOp->hasNoSignedWrap()) {
+            // If initial value of recurrence is nonnegative, and we are adding
+            // a nonnegative number with nsw, the result can only be nonnegative
+            // or poison value regardless of the number of times we execute the
+            // add in phi recurrence. If initial value is negative and we are
+            // adding a negative number with nsw, the result can only be
+            // negative or poison value. Similar arguments apply to sub and mul.
+            //
+            // (add non-negative, non-negative) --> non-negative
+            // (add negative, negative) --> negative
+            if (Opcode == Instruction::Add) {
+              if (KnownZero2.isNegative() && KnownZero3.isNegative())
+                KnownZero.setBit(BitWidth - 1);
+              else if (KnownOne2.isNegative() && KnownOne3.isNegative())
+                KnownOne.setBit(BitWidth - 1);
+            }
+
+            // (sub nsw non-negative, negative) --> non-negative
+            // (sub nsw negative, non-negative) --> negative
+            else if (Opcode == Instruction::Sub && LL == I) {
+              if (KnownZero2.isNegative() && KnownOne3.isNegative())
+                KnownZero.setBit(BitWidth - 1);
+              else if (KnownOne2.isNegative() && KnownZero3.isNegative())
+                KnownOne.setBit(BitWidth - 1);
+            }
+
+            // (mul nsw non-negative, non-negative) --> non-negative
+            else if (Opcode == Instruction::Mul && KnownZero2.isNegative() &&
+                     KnownZero3.isNegative())
+              KnownZero.setBit(BitWidth - 1);
+          }
+
           break;
         }
       }
Index: test/Transforms/BBVectorize/loop1.ll
===================================================================
--- test/Transforms/BBVectorize/loop1.ll
+++ test/Transforms/BBVectorize/loop1.ll
@@ -83,7 +83,7 @@
 ; CHECK-UNRL: %add12 = fadd <2 x double> %add7, %mul11
 ; CHECK-UNRL: %4 = bitcast double* %arrayidx14 to <2 x double>*
 ; CHECK-UNRL: store <2 x double> %add12, <2 x double>* %4, align 8
-; CHECK-UNRL: %indvars.iv.next.1 = add nsw i64 %indvars.iv, 2
+; CHECK-UNRL: %indvars.iv.next.1 = add nuw nsw i64 %indvars.iv, 2
 ; CHECK-UNRL: %lftr.wideiv.1 = trunc i64 %indvars.iv.next.1 to i32
 ; CHECK-UNRL: %exitcond.1 = icmp eq i32 %lftr.wideiv.1, 10
 ; CHECK-UNRL: br i1 %exitcond.1, label %for.end, label %for.body


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D18777.73080.patch
Type: text/x-patch
Size: 3263 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20160930/302fb2d3/attachment.bin>