[llvm] r278267 - [ValueTracking] An improvement to IR ValueTracking on Non-negative Integers
Andrew Kaylor via llvm-commits
llvm-commits at lists.llvm.org
Wed Aug 10 11:47:20 PDT 2016
Author: akaylor
Date: Wed Aug 10 13:47:19 2016
New Revision: 278267
URL: http://llvm.org/viewvc/llvm-project?rev=278267&view=rev
Log:
[ValueTracking] An improvement to IR ValueTracking on Non-negative Integers
Patch by Li Huang
Differential Revision: https://reviews.llvm.org/D18777
Added:
llvm/trunk/test/Analysis/ValueTracking/iv-known-sign.ll
Modified:
llvm/trunk/lib/Analysis/ValueTracking.cpp
llvm/trunk/test/Transforms/BBVectorize/loop1.ll
Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=278267&r1=278266&r2=278267&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Wed Aug 10 13:47:19 2016
@@ -1272,7 +1272,9 @@ static void computeKnownBitsFromOperator
unsigned Opcode = LU->getOpcode();
// Check for operations that have the property that if
// both their operands have low zero bits, the result
- // will have low zero bits.
+ // will have low zero bits. Also check for operations
+ // that are known to produce non-negative or negative
+ // recurrence values.
if (Opcode == Instruction::Add ||
Opcode == Instruction::Sub ||
Opcode == Instruction::And ||
@@ -1298,6 +1300,40 @@ static void computeKnownBitsFromOperator
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;
}
}
Added: llvm/trunk/test/Analysis/ValueTracking/iv-known-sign.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ValueTracking/iv-known-sign.ll?rev=278267&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/ValueTracking/iv-known-sign.ll (added)
+++ llvm/trunk/test/Analysis/ValueTracking/iv-known-sign.ll Wed Aug 10 13:47:19 2016
@@ -0,0 +1,97 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+; Induction variable is known to be non-negative
+; when its initial value is non-negative and
+; increments by non-negative value
+define i32 @test_indvar_nonnegative_add() {
+; CHECK-LABEL: @test_indvar_nonnegative_add(
+; CHECK: br i1 true, label %for.end, label %for.body
+entry:
+ br label %for.body
+
+for.body:
+ %i = phi i32 [0, %entry], [%inc, %for.body]
+ %inc = add nsw i32 %i, 1
+ %cmp = icmp sge i32 %i, 0
+ br i1 %cmp, label %for.end, label %for.body
+
+for.end:
+ ret i32 %i
+}
+
+; Induction variable is known to be non-negative
+; when its initial value is non-negative and
+; is multiplied by a non-negative value in each
+; iteration
+define i32 @test_indvar_nonnegative_mul() {
+; CHECK-LABEL: @test_indvar_nonnegative_mul(
+; CHECK: br i1 true, label %for.end, label %for.body
+entry:
+ br label %for.body
+
+for.body:
+ %i = phi i32 [1, %entry], [%inc, %for.body]
+ %inc = mul nsw i32 %i, 3
+ %cmp = icmp sge i32 %i, 0
+ br i1 %cmp, label %for.end, label %for.body
+
+for.end:
+ ret i32 %i
+}
+
+; Induction variable is known to be non-negative,
+; Similar to add
+define i32 @test_indvar_nonnegative_sub(i32 %a) {
+; CHECK-LABEL: @test_indvar_nonnegative_sub(
+; CHECK: br i1 true, label %for.end, label %for.body
+entry:
+ br label %for.body
+
+for.body:
+ %i = phi i32 [0, %entry], [%inc, %for.body]
+ %b = or i32 %a, -2147483648
+ %inc = sub nsw i32 %i, %b
+ %cmp = icmp sge i32 %i, 0
+ br i1 %cmp, label %for.end, label %for.body
+
+for.end:
+ ret i32 %i
+}
+
+; Induction variable is known to be negative when
+; its initial value is negative and decrements by
+; a non-negative value
+define i32 @test_indvar_negative_add() {
+; CHECK-LABEL: @test_indvar_negative_add(
+; CHECK: br i1 true, label %for.end, label %for.body
+entry:
+ br label %for.body
+
+for.body:
+ %i = phi i32 [-1, %entry], [%inc, %for.body]
+ %inc = add nsw i32 %i, -1
+ %cmp = icmp slt i32 %i, 0
+ br i1 %cmp, label %for.end, label %for.body
+
+for.end:
+ ret i32 %i
+}
+
+; Induction variable is known to be negative,
+; similar to add
+define i32 @test_indvar_negative_sub(i32 %a) {
+; CHECK-LABEL: @test_indvar_negative_sub(
+; CHECK: br i1 true, label %for.end, label %for.body
+entry:
+ br label %for.body
+
+for.body:
+ %i = phi i32 [-1, %entry], [%inc, %for.body]
+ %b = and i32 %a, 2147483647
+ %inc = sub nsw i32 %i, %b
+ %cmp = icmp slt i32 %i, 0
+ br i1 %cmp, label %for.end, label %for.body
+
+for.end:
+ ret i32 %i
+}
Modified: llvm/trunk/test/Transforms/BBVectorize/loop1.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/BBVectorize/loop1.ll?rev=278267&r1=278266&r2=278267&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/BBVectorize/loop1.ll (original)
+++ llvm/trunk/test/Transforms/BBVectorize/loop1.ll Wed Aug 10 13:47:19 2016
@@ -83,7 +83,7 @@ for.body:
; 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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