return BinaryOperator::CreateAdd(Add, Builder->CreateMul(C1, CI));
}
}
+
+ // (1 - X) * (-2) -> (x - 1) * 2, for all positive nonzero powers of 2
+ // The "* 2" thus becomes a potential shifting opportunity.
+ {
+ const APInt & Val = CI->getValue();
+ const APInt &PosVal = Val.abs();
+ if (Val.isNegative() && PosVal.isPowerOf2()) {
+ Value *X = 0;
+ if (match(Op0, m_Sub(m_One(), m_Value(X)))) {
+ // ConstantInt::get(Op0->getType(), 2);
+ Value *Sub = Builder->CreateSub(X, ConstantInt::get(X->getType(), 1),
+ "dec1");
+ return BinaryOperator::CreateMul(Sub, ConstantInt::get(X->getType(),
+ PosVal));
+ }
+ }
+ }
}
// Simplify mul instructions with a constant RHS.
--- /dev/null
+; ModuleID = 'test1.c'
+; RUN: opt -S -instcombine < %s | FileCheck %s
+target triple = "x86_64-apple-macosx10.6.6"
+
+define zeroext i16 @foo(i32 %on_off, i16* %puls) nounwind uwtable ssp {
+entry:
+ %on_off.addr = alloca i32, align 4
+ %puls.addr = alloca i16*, align 8
+ %a = alloca i32, align 4
+ store i32 %on_off, i32* %on_off.addr, align 4
+ store i16* %puls, i16** %puls.addr, align 8
+ %tmp = load i32* %on_off.addr, align 4
+; CHECK-NOT: sub
+; CHECK-NOT: mul
+; (1 - %tmp) * (-2) -> (%tmp - 1) * 2
+ %sub = sub i32 1, %tmp
+ %mul = mul i32 %sub, -2
+; CHECK: shl
+; CHECK-NEXT: add
+ store i32 %mul, i32* %a, align 4
+ %tmp1 = load i32* %a, align 4
+ %conv = trunc i32 %tmp1 to i16
+ ret i16 %conv
+}