[PATCH] D18777: [ValueTracking] An improvement to IR ValueTracking on Non-negative Integers
Li Huang via llvm-commits
llvm-commits at lists.llvm.org
Fri Sep 30 10:06:40 PDT 2016
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
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