[llvm] r294898 - [InstCombine] fold icmp sgt/slt (add nsw X, C2), C --> icmp sgt/slt X, (C - C2)
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Sun Feb 12 08:40:30 PST 2017
Author: spatel
Date: Sun Feb 12 10:40:30 2017
New Revision: 294898
URL: http://llvm.org/viewvc/llvm-project?rev=294898&view=rev
Log:
[InstCombine] fold icmp sgt/slt (add nsw X, C2), C --> icmp sgt/slt X, (C - C2)
I found one special case of this transform for 'slt 0', so I removed that and added the general transform.
Alive code to check correctness:
Name: slt_no_overflow
Pre: WillNotOverflowSignedSub(C1, C2)
%a = add nsw i8 %x, C2
%b = icmp slt %a, C1
=>
%b = icmp slt %x, C1 - C2
Name: sgt_no_overflow
Pre: WillNotOverflowSignedSub(C1, C2)
%a = add nsw i8 %x, C2
%b = icmp sgt %a, C1
=>
%b = icmp sgt %x, C1 - C2
http://rise4fun.com/Alive/MH
Differential Revision: https://reviews.llvm.org/D29774
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
llvm/trunk/test/Transforms/InstCombine/icmp-add.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=294898&r1=294897&r2=294898&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Sun Feb 12 10:40:30 2017
@@ -2373,6 +2373,22 @@ Instruction *InstCombiner::foldICmpAddCo
Value *X = Add->getOperand(0);
Type *Ty = Add->getType();
CmpInst::Predicate Pred = Cmp.getPredicate();
+
+ // If the add does not wrap, we can always adjust the compare by subtracting
+ // the constants. Equality comparisons are handled elsewhere. SGE/SLE are
+ // canonicalized to SGT/SLT.
+ if (Add->hasNoSignedWrap() &&
+ (Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SLT)) {
+ bool Overflow;
+ APInt NewC = C->ssub_ov(*C2, Overflow);
+ // If there is overflow, the result must be true or false.
+ // TODO: Can we assert there is no overflow because InstSimplify always
+ // handles those cases?
+ if (!Overflow)
+ // icmp Pred (add nsw X, C2), C --> icmp Pred X, (C - C2)
+ return new ICmpInst(Pred, X, ConstantInt::get(Ty, NewC));
+ }
+
auto CR = ConstantRange::makeExactICmpRegion(Pred, *C).subtract(*C2);
const APInt &Upper = CR.getUpper();
const APInt &Lower = CR.getLower();
@@ -2795,12 +2811,6 @@ Instruction *InstCombiner::foldICmpBinOp
D = BO1->getOperand(1);
}
- // icmp (X+cst) < 0 --> X < -cst
- if (NoOp0WrapProblem && ICmpInst::isSigned(Pred) && match(Op1, m_Zero()))
- if (ConstantInt *RHSC = dyn_cast_or_null<ConstantInt>(B))
- if (!RHSC->isMinValue(/*isSigned=*/true))
- return new ICmpInst(Pred, A, ConstantExpr::getNeg(RHSC));
-
// icmp (X+Y), X -> icmp Y, 0 for equalities or if there is no overflow.
if ((A == Op1 || B == Op1) && NoOp0WrapProblem)
return new ICmpInst(Pred, A == Op1 ? B : A,
Modified: llvm/trunk/test/Transforms/InstCombine/icmp-add.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp-add.ll?rev=294898&r1=294897&r2=294898&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/icmp-add.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/icmp-add.ll Sun Feb 12 10:40:30 2017
@@ -88,8 +88,7 @@ define <2 x i1> @test4vec(<2 x i32> %a)
define i1 @nsw_slt1(i8 %a) {
; CHECK-LABEL: @nsw_slt1(
-; CHECK-NEXT: [[B:%.*]] = add nsw i8 %a, 100
-; CHECK-NEXT: [[C:%.*]] = icmp slt i8 [[B]], -27
+; CHECK-NEXT: [[C:%.*]] = icmp eq i8 %a, -128
; CHECK-NEXT: ret i1 [[C]]
;
%b = add nsw i8 %a, 100
@@ -102,8 +101,7 @@ define i1 @nsw_slt1(i8 %a) {
define i1 @nsw_slt2(i8 %a) {
; CHECK-LABEL: @nsw_slt2(
-; CHECK-NEXT: [[B:%.*]] = add nsw i8 %a, -100
-; CHECK-NEXT: [[C:%.*]] = icmp slt i8 [[B]], 27
+; CHECK-NEXT: [[C:%.*]] = icmp ne i8 %a, 127
; CHECK-NEXT: ret i1 [[C]]
;
%b = add nsw i8 %a, -100
@@ -116,8 +114,7 @@ define i1 @nsw_slt2(i8 %a) {
define i1 @nsw_slt3(i8 %a) {
; CHECK-LABEL: @nsw_slt3(
-; CHECK-NEXT: [[B:%.*]] = add nsw i8 %a, 100
-; CHECK-NEXT: [[C:%.*]] = icmp slt i8 [[B]], -26
+; CHECK-NEXT: [[C:%.*]] = icmp slt i8 %a, -126
; CHECK-NEXT: ret i1 [[C]]
;
%b = add nsw i8 %a, 100
@@ -130,8 +127,7 @@ define i1 @nsw_slt3(i8 %a) {
define i1 @nsw_slt4(i8 %a) {
; CHECK-LABEL: @nsw_slt4(
-; CHECK-NEXT: [[B:%.*]] = add nsw i8 %a, -100
-; CHECK-NEXT: [[C:%.*]] = icmp slt i8 [[B]], 26
+; CHECK-NEXT: [[C:%.*]] = icmp slt i8 %a, 126
; CHECK-NEXT: ret i1 [[C]]
;
%b = add nsw i8 %a, -100
@@ -144,8 +140,7 @@ define i1 @nsw_slt4(i8 %a) {
define i1 @nsw_sgt1(i8 %a) {
; CHECK-LABEL: @nsw_sgt1(
-; CHECK-NEXT: [[B:%.*]] = add nsw i8 %a, -100
-; CHECK-NEXT: [[C:%.*]] = icmp sgt i8 [[B]], 26
+; CHECK-NEXT: [[C:%.*]] = icmp eq i8 %a, 127
; CHECK-NEXT: ret i1 [[C]]
;
%b = add nsw i8 %a, -100
@@ -155,11 +150,11 @@ define i1 @nsw_sgt1(i8 %a) {
; icmp Pred (add nsw X, C2), C --> icmp Pred X, (C - C2), when C - C2 does not overflow.
; Try a vector type to make sure that works too.
+; FIXME: This should be 'eq 127' as above.
define <2 x i1> @nsw_sgt2_splat_vec(<2 x i8> %a) {
; CHECK-LABEL: @nsw_sgt2_splat_vec(
-; CHECK-NEXT: [[B:%.*]] = add nsw <2 x i8> %a, <i8 100, i8 100>
-; CHECK-NEXT: [[C:%.*]] = icmp sgt <2 x i8> [[B]], <i8 -26, i8 -26>
+; CHECK-NEXT: [[C:%.*]] = icmp sgt <2 x i8> %a, <i8 -126, i8 -126>
; CHECK-NEXT: ret <2 x i1> [[C]]
;
%b = add nsw <2 x i8> %a, <i8 100, i8 100>
@@ -180,12 +175,11 @@ define i1 @slt_zero_add_nsw(i32 %a) {
ret i1 %cmp
}
-; FIXME: The same fold should work with vectors.
+; The same fold should work with vectors.
define <2 x i1> @slt_zero_add_nsw_splat_vec(<2 x i8> %a) {
; CHECK-LABEL: @slt_zero_add_nsw_splat_vec(
-; CHECK-NEXT: [[ADD:%.*]] = add nsw <2 x i8> %a, <i8 1, i8 1>
-; CHECK-NEXT: [[CMP:%.*]] = icmp slt <2 x i8> [[ADD]], zeroinitializer
+; CHECK-NEXT: [[CMP:%.*]] = icmp slt <2 x i8> %a, <i8 -1, i8 -1>
; CHECK-NEXT: ret <2 x i1> [[CMP]]
;
%add = add nsw <2 x i8> %a, <i8 1, i8 1>
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