[llvm] r305792 - [InstCombine] try to canonicalize xor-of-icmps to and-of-icmps
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Tue Jun 20 05:40:55 PDT 2017
Author: spatel
Date: Tue Jun 20 07:40:55 2017
New Revision: 305792
URL: http://llvm.org/viewvc/llvm-project?rev=305792&view=rev
Log:
[InstCombine] try to canonicalize xor-of-icmps to and-of-icmps
We have a large portfolio of folds for and-of-icmps and or-of-icmps in InstSimplify and InstCombine,
but hardly anything for xor-of-icmps. Rather than trying to rethink and translate all of those folds,
we can use the truth table definition of xor:
X ^ Y --> (X | Y) & !(X & Y)
...to see if we can convert the xor to and/or and then use the existing folds.
http://rise4fun.com/Alive/J9v
Differential Revision: https://reviews.llvm.org/D33342
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
llvm/trunk/test/Transforms/InstCombine/set.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp?rev=305792&r1=305791&r2=305792&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp Tue Jun 20 07:40:55 2017
@@ -2351,6 +2351,30 @@ Value *InstCombiner::foldXorOfICmps(ICmp
}
}
+ // Instead of trying to imitate the folds for and/or, decompose this 'xor'
+ // into those logic ops. That is, try to turn this into an and-of-icmps
+ // because we have many folds for that pattern.
+ //
+ // This is based on a truth table definition of xor:
+ // X ^ Y --> (X | Y) & !(X & Y)
+ if (Value *OrICmp = SimplifyBinOp(Instruction::Or, LHS, RHS, SQ)) {
+ // TODO: If OrICmp is true, then the definition of xor simplifies to !(X&Y).
+ // TODO: If OrICmp is false, the whole thing is false (InstSimplify?).
+ if (Value *AndICmp = SimplifyBinOp(Instruction::And, LHS, RHS, SQ)) {
+ // TODO: Independently handle cases where the 'and' side is a constant.
+ if (OrICmp == LHS && AndICmp == RHS && RHS->hasOneUse()) {
+ // (LHS | RHS) & !(LHS & RHS) --> LHS & !RHS
+ RHS->setPredicate(RHS->getInversePredicate());
+ return Builder->CreateAnd(LHS, RHS);
+ }
+ if (OrICmp == RHS && AndICmp == LHS && LHS->hasOneUse()) {
+ // !(LHS & RHS) & (LHS | RHS) --> !LHS & !RHS
+ LHS->setPredicate(LHS->getInversePredicate());
+ return Builder->CreateAnd(LHS, RHS);
+ }
+ }
+ }
+
return nullptr;
}
Modified: llvm/trunk/test/Transforms/InstCombine/set.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/set.ll?rev=305792&r1=305791&r2=305792&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/set.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/set.ll Tue Jun 20 07:40:55 2017
@@ -164,10 +164,8 @@ define i1 @bool_eq0(i64 %a) {
define i1 @xor_of_icmps(i64 %a) {
; CHECK-LABEL: @xor_of_icmps(
-; CHECK-NEXT: [[B:%.*]] = icmp sgt i64 %a, 0
-; CHECK-NEXT: [[C:%.*]] = icmp eq i64 %a, 1
-; CHECK-NEXT: [[XOR:%.*]] = xor i1 [[C]], [[B]]
-; CHECK-NEXT: ret i1 [[XOR]]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp sgt i64 %a, 1
+; CHECK-NEXT: ret i1 [[TMP1]]
;
%b = icmp sgt i64 %a, 0
%c = icmp eq i64 %a, 1
@@ -179,10 +177,8 @@ define i1 @xor_of_icmps(i64 %a) {
define i1 @xor_of_icmps_commute(i64 %a) {
; CHECK-LABEL: @xor_of_icmps_commute(
-; CHECK-NEXT: [[B:%.*]] = icmp sgt i64 %a, 0
-; CHECK-NEXT: [[C:%.*]] = icmp eq i64 %a, 1
-; CHECK-NEXT: [[XOR:%.*]] = xor i1 [[B]], [[C]]
-; CHECK-NEXT: ret i1 [[XOR]]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp sgt i64 %a, 1
+; CHECK-NEXT: ret i1 [[TMP1]]
;
%b = icmp sgt i64 %a, 0
%c = icmp eq i64 %a, 1
@@ -209,10 +205,10 @@ define i1 @xor_of_icmps_folds_more(i64 %
define i32 @PR2844(i32 %x) {
; CHECK-LABEL: @PR2844(
-; CHECK-NEXT: [[A:%.*]] = icmp eq i32 %x, 0
+; CHECK-NEXT: [[A:%.*]] = icmp ne i32 %x, 0
; CHECK-NEXT: [[B:%.*]] = icmp sgt i32 %x, -638208502
-; CHECK-NEXT: [[NOT_OR:%.*]] = xor i1 [[A]], [[B]]
-; CHECK-NEXT: [[SEL:%.*]] = zext i1 [[NOT_OR]] to i32
+; CHECK-NEXT: [[TMP1:%.*]] = and i1 [[A]], [[B]]
+; CHECK-NEXT: [[SEL:%.*]] = zext i1 [[TMP1]] to i32
; CHECK-NEXT: ret i32 [[SEL]]
;
%A = icmp eq i32 %x, 0
More information about the llvm-commits
mailing list