From d8e175bca5919de13fe003cab6b10f23af3d055d Mon Sep 17 00:00:00 2001
From: Roman Lebedev <lebedev.ri@gmail.com>
Date: Sat, 14 Jul 2018 16:44:54 +0000
Subject: [PATCH] [InstCombine] Fold  x u<= x & C  to  x u<= C

https://bugs.llvm.org/show_bug.cgi?id=38123
https://rise4fun.com/Alive/Fqp

This pattern is not commutative. But InstSimplify will
already have taken care of the 'commutative' variant.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337102 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../InstCombine/InstCombineCompares.cpp       |  5 +++
 ...t-low-bit-mask-and-icmp-ule-to-icmp-ule.ll | 34 ++++++++-----------
 2 files changed, 19 insertions(+), 20 deletions(-)

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 1024cbafaaa..2a8d83fde2c 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2907,6 +2907,11 @@ static Value *foldICmpWithLowBitMaskedVal(ICmpInst &I,
     assert(X == I.getOperand(1) && "instsimplify took care of commut. variant");
     DstPred = ICmpInst::Predicate::ICMP_UGT;
     break;
+  case ICmpInst::Predicate::ICMP_ULE:
+    //  x u<= x & (-1 >> y)    ->    x u<= (-1 >> y)
+    assert(X == I.getOperand(0) && "instsimplify took care of commut. variant");
+    DstPred = ICmpInst::Predicate::ICMP_ULE;
+    break;
   // TODO: more folds are possible, https://bugs.llvm.org/show_bug.cgi?id=38123
   default:
     return nullptr;
diff --git a/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-ule-to-icmp-ule.ll b/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-ule-to-icmp-ule.ll
index f29623f171e..0bab709618d 100644
--- a/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-ule-to-icmp-ule.ll
+++ b/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-ule-to-icmp-ule.ll
@@ -20,9 +20,8 @@ declare <3 x i8> @gen3x8()
 define i1 @p0() {
 ; CHECK-LABEL: @p0(
 ; CHECK-NEXT:    [[X:%.*]] = call i8 @gen8()
-; CHECK-NEXT:    [[TMP0:%.*]] = and i8 [[X]], 3
-; CHECK-NEXT:    [[RET:%.*]] = icmp ule i8 [[X]], [[TMP0]]
-; CHECK-NEXT:    ret i1 [[RET]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ult i8 [[X]], 4
+; CHECK-NEXT:    ret i1 [[TMP1]]
 ;
   %x = call i8 @gen8()
   %tmp0 = and i8 %x, 3
@@ -34,9 +33,8 @@ define i1 @pv(i8 %y) {
 ; CHECK-LABEL: @pv(
 ; CHECK-NEXT:    [[X:%.*]] = call i8 @gen8()
 ; CHECK-NEXT:    [[TMP0:%.*]] = lshr i8 -1, [[Y:%.*]]
-; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[TMP0]], [[X]]
-; CHECK-NEXT:    [[RET:%.*]] = icmp ule i8 [[X]], [[TMP1]]
-; CHECK-NEXT:    ret i1 [[RET]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ule i8 [[X]], [[TMP0]]
+; CHECK-NEXT:    ret i1 [[TMP1]]
 ;
   %x = call i8 @gen8()
   %tmp0 = lshr i8 -1, %y
@@ -52,9 +50,8 @@ define i1 @pv(i8 %y) {
 define <2 x i1> @p1_vec_splat() {
 ; CHECK-LABEL: @p1_vec_splat(
 ; CHECK-NEXT:    [[X:%.*]] = call <2 x i8> @gen2x8()
-; CHECK-NEXT:    [[TMP0:%.*]] = and <2 x i8> [[X]], <i8 3, i8 3>
-; CHECK-NEXT:    [[RET:%.*]] = icmp ule <2 x i8> [[X]], [[TMP0]]
-; CHECK-NEXT:    ret <2 x i1> [[RET]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ult <2 x i8> [[X]], <i8 4, i8 4>
+; CHECK-NEXT:    ret <2 x i1> [[TMP1]]
 ;
   %x = call <2 x i8> @gen2x8()
   %tmp0 = and <2 x i8> %x, <i8 3, i8 3>
@@ -65,9 +62,8 @@ define <2 x i1> @p1_vec_splat() {
 define <2 x i1> @p2_vec_nonsplat() {
 ; CHECK-LABEL: @p2_vec_nonsplat(
 ; CHECK-NEXT:    [[X:%.*]] = call <2 x i8> @gen2x8()
-; CHECK-NEXT:    [[TMP0:%.*]] = and <2 x i8> [[X]], <i8 3, i8 15>
-; CHECK-NEXT:    [[RET:%.*]] = icmp ule <2 x i8> [[X]], [[TMP0]]
-; CHECK-NEXT:    ret <2 x i1> [[RET]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ult <2 x i8> [[X]], <i8 4, i8 16>
+; CHECK-NEXT:    ret <2 x i1> [[TMP1]]
 ;
   %x = call <2 x i8> @gen2x8()
   %tmp0 = and <2 x i8> %x, <i8 3, i8 15> ; doesn't have to be splat.
@@ -78,9 +74,8 @@ define <2 x i1> @p2_vec_nonsplat() {
 define <3 x i1> @p3_vec_splat_undef() {
 ; CHECK-LABEL: @p3_vec_splat_undef(
 ; CHECK-NEXT:    [[X:%.*]] = call <3 x i8> @gen3x8()
-; CHECK-NEXT:    [[TMP0:%.*]] = and <3 x i8> [[X]], <i8 3, i8 undef, i8 3>
-; CHECK-NEXT:    [[RET:%.*]] = icmp ule <3 x i8> [[X]], [[TMP0]]
-; CHECK-NEXT:    ret <3 x i1> [[RET]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ult <3 x i8> [[X]], <i8 4, i8 undef, i8 4>
+; CHECK-NEXT:    ret <3 x i1> [[TMP1]]
 ;
   %x = call <3 x i8> @gen3x8()
   %tmp0 = and <3 x i8> %x, <i8 3, i8 undef, i8 3>
@@ -109,9 +104,8 @@ define i1 @cv0(i8 %y) {
 ; CHECK-LABEL: @cv0(
 ; CHECK-NEXT:    [[X:%.*]] = call i8 @gen8()
 ; CHECK-NEXT:    [[TMP0:%.*]] = lshr i8 -1, [[Y:%.*]]
-; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[TMP0]], [[X]]
-; CHECK-NEXT:    [[RET:%.*]] = icmp ule i8 [[X]], [[TMP1]]
-; CHECK-NEXT:    ret i1 [[RET]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ule i8 [[X]], [[TMP0]]
+; CHECK-NEXT:    ret i1 [[TMP1]]
 ;
   %x = call i8 @gen8()
   %tmp0 = lshr i8 -1, %y
@@ -153,8 +147,8 @@ define i1 @oneuse0() {
 ; CHECK-NEXT:    [[X:%.*]] = call i8 @gen8()
 ; CHECK-NEXT:    [[TMP0:%.*]] = and i8 [[X]], 3
 ; CHECK-NEXT:    call void @use8(i8 [[TMP0]])
-; CHECK-NEXT:    [[RET:%.*]] = icmp ule i8 [[X]], [[TMP0]]
-; CHECK-NEXT:    ret i1 [[RET]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ult i8 [[X]], 4
+; CHECK-NEXT:    ret i1 [[TMP1]]
 ;
   %x = call i8 @gen8()
   %tmp0 = and i8 %x, 3
-- 
2.50.1