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 ||
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;
}
}
--- /dev/null
+; 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
+}