From 49064ff7708bcd3b720ce79bc7629c2f3207b8d6 Mon Sep 17 00:00:00 2001
From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Sat, 24 Dec 2011 17:31:53 +0000
Subject: [PATCH] InstCombine: Add a combine that turns (2^n)-1 ^ x back into
(2^n)-1 - x iff x is smaller than 2^n and it fuses with a following add.
This was intended to undo the sub canonicalization in cases where it's not profitable, but it also
finds some cases on it's own.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147256 91177308-0d34-0410-b5e6-96231b3b80d8
---
lib/Transforms/InstCombine/InstCombineAddSub.cpp | 13 +++++++++++++
test/Transforms/InstCombine/sub-xor.ll | 12 ++++++++++++
2 files changed, 25 insertions(+)
diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 604d9c8bb44..f2be01b73be 100644
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -136,6 +136,19 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
Value *NewShl = Builder->CreateShl(XorLHS, ShAmt, "sext");
return BinaryOperator::CreateAShr(NewShl, ShAmt);
}
+
+ // If this is a xor that was canonicalized from a sub, turn it back into
+ // a sub and fuse this add with it.
+ if (LHS->hasOneUse() && (XorRHS->getValue()+1).isPowerOf2()) {
+ IntegerType *IT = cast<IntegerType>(I.getType());
+ APInt Mask = APInt::getAllOnesValue(IT->getBitWidth());
+ APInt LHSKnownOne(IT->getBitWidth(), 0);
+ APInt LHSKnownZero(IT->getBitWidth(), 0);
+ ComputeMaskedBits(XorLHS, Mask, LHSKnownZero, LHSKnownOne);
+ if ((XorRHS->getValue() | LHSKnownZero).isAllOnesValue())
+ return BinaryOperator::CreateSub(ConstantExpr::getAdd(XorRHS, CI),
+ XorLHS);
+ }
}
}
diff --git a/test/Transforms/InstCombine/sub-xor.ll b/test/Transforms/InstCombine/sub-xor.ll
index bfa9f408c6f..279e4aca9de 100644
--- a/test/Transforms/InstCombine/sub-xor.ll
+++ b/test/Transforms/InstCombine/sub-xor.ll
@@ -23,3 +23,15 @@ define i32 @test2(i32 %x) nounwind {
; CHECK-NEXT: xor i32 %count, 31
; CHECK-NEXT: ret
}
+
+define i32 @test3(i32 %x) nounwind {
+ %and = and i32 %x, 31
+ %sub = xor i32 31, %and
+ %add = add i32 %sub, 42
+ ret i32 %add
+
+; CHECK: @test3
+; CHECK-NEXT: and i32 %x, 31
+; CHECK-NEXT: sub i32 73, %and
+; CHECK-NEXT: ret
+}
--
2.34.1