[InstCombine] Simplify icmp ult/uge (shl %x, C2), C1 iff C1 is power of two -> icmp eq/ne (and %x, (lshr -C1, C2)), 0.

Simplify 'shl' inequality test into 'and' equality test.

This pattern happens in the middle-end while simplifying bitfield access,
Exposed in https://reviews.llvm.org/D63505

https://rise4fun.com/Alive/6uz

Reviewers: lebedev.ri, efriedma

Reviewed By: lebedev.ri

Subscribers: spatel, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63675

llvm-svn: 364348

3 files changed, 47 insertions, 26 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index c62e2ba843c..29ac729682d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2028,6 +2028,27 @@ Instruction *InstCombiner::foldICmpShlConstant(ICmpInst &Cmp,
                         And, Constant::getNullValue(ShType));
   }
 
+  // Simplify 'shl' inequality test into 'and' equality test.
+  if (Cmp.isUnsigned() && Shl->hasOneUse()) {
+    // (X l<< C2) u<=/u> C1 iff C1+1 is power of two -> X & (~C1 l>> C2) ==/!= 0
+    if ((C + 1).isPowerOf2() &&
+        (Pred == ICmpInst::ICMP_ULE || Pred == ICmpInst::ICMP_UGT)) {
+      Value *And = Builder.CreateAnd(X, (~C).lshr(ShiftAmt->getZExtValue()));
+      return new ICmpInst(Pred == ICmpInst::ICMP_ULE ? ICmpInst::ICMP_EQ
+                                                     : ICmpInst::ICMP_NE,
+                          And, Constant::getNullValue(ShType));
+    }
+    // (X l<< C2) u</u>= C1 iff C1 is power of two -> X & (-C1 l>> C2) ==/!= 0
+    if (C.isPowerOf2() &&
+        (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_UGE)) {
+      Value *And =
+          Builder.CreateAnd(X, (~(C - 1)).lshr(ShiftAmt->getZExtValue()));
+      return new ICmpInst(Pred == ICmpInst::ICMP_ULT ? ICmpInst::ICMP_EQ
+                                                     : ICmpInst::ICMP_NE,
+                          And, Constant::getNullValue(ShType));
+    }
+  }
+
   // Transform (icmp pred iM (shl iM %v, N), C)
   // -> (icmp pred i(M-N) (trunc %v iM to i(M-N)), (trunc (C>>N))
   // Transform the shl to a trunc if (trunc (C>>N)) has no loss and M-N.
diff --git a/llvm/test/Transforms/InstCombine/pr17827.ll b/llvm/test/Transforms/InstCombine/pr17827.ll
index 40b050d65b2..7521f819a1e 100644
--- a/llvm/test/Transforms/InstCombine/pr17827.ll
+++ b/llvm/test/Transforms/InstCombine/pr17827.ll
@@ -66,8 +66,8 @@ define <2 x i1> @test_shift_and_cmp_changed1_vec(<2 x i8> %p, <2 x i8> %q) {
 ; Unsigned compare allows a transformation to compare against 0.
 define i1 @test_shift_and_cmp_changed2(i8 %p) {
 ; CHECK-LABEL: @test_shift_and_cmp_changed2(
-; CHECK-NEXT:    [[SHLP:%.*]] = shl i8 [[P:%.*]], 5
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i8 [[SHLP]], 64
+; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[P:%.*]], 6
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[TMP1]], 0
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %shlp = shl i8 %p, 5
@@ -78,8 +78,8 @@ define i1 @test_shift_and_cmp_changed2(i8 %p) {
 
 define <2 x i1> @test_shift_and_cmp_changed2_vec(<2 x i8> %p) {
 ; CHECK-LABEL: @test_shift_and_cmp_changed2_vec(
-; CHECK-NEXT:    [[SHLP:%.*]] = shl <2 x i8> [[P:%.*]], <i8 5, i8 5>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult <2 x i8> [[SHLP]], <i8 64, i8 64>
+; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i8> [[P:%.*]], <i8 6, i8 6>
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq <2 x i8> [[TMP1]], zeroinitializer
 ; CHECK-NEXT:    ret <2 x i1> [[CMP]]
 ;
   %shlp = shl <2 x i8> %p, <i8 5, i8 5>
diff --git a/llvm/test/Transforms/InstCombine/shl-unsigned-cmp-const.ll b/llvm/test/Transforms/InstCombine/shl-unsigned-cmp-const.ll
index cd5cd6650c9..db51ccf40d8 100644
--- a/llvm/test/Transforms/InstCombine/shl-unsigned-cmp-const.ll
+++ b/llvm/test/Transforms/InstCombine/shl-unsigned-cmp-const.ll
@@ -9,8 +9,8 @@
 ; C2 Shift amount smaller than C1 trailing zeros.
 define i1 @scalar_i8_shl_ult_const_1(i8 %x) {
 ; CHECK-LABEL: @scalar_i8_shl_ult_const_1(
-; CHECK-NEXT:    [[SHL:%.*]] = shl i8 [[X:%.*]], 5
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i8 [[SHL]], 64
+; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[X:%.*]], 6
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[TMP1]], 0
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %shl = shl i8 %x, 5
@@ -45,8 +45,8 @@ define i1 @scalar_i8_shl_ult_const_3(i8 %x) {
 ; C2 Shift amount smaller than C1 trailing zeros.
 define i1 @scalar_i16_shl_ult_const(i16 %x) {
 ; CHECK-LABEL: @scalar_i16_shl_ult_const(
-; CHECK-NEXT:    [[SHL:%.*]] = shl i16 [[X:%.*]], 8
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i16 [[SHL]], 1024
+; CHECK-NEXT:    [[TMP1:%.*]] = and i16 [[X:%.*]], 252
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i16 [[TMP1]], 0
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %shl = shl i16 %x, 8
@@ -56,8 +56,8 @@ define i1 @scalar_i16_shl_ult_const(i16 %x) {
 
 define i1 @scalar_i32_shl_ult_const(i32 %x) {
 ; CHECK-LABEL: @scalar_i32_shl_ult_const(
-; CHECK-NEXT:    [[SHL:%.*]] = shl i32 [[X:%.*]], 11
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i32 [[SHL]], 131072
+; CHECK-NEXT:    [[TMP1:%.*]] = and i32 [[X:%.*]], 2097088
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[TMP1]], 0
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %shl = shl i32 %x, 11
@@ -67,8 +67,8 @@ define i1 @scalar_i32_shl_ult_const(i32 %x) {
 
 define i1 @scalar_i64_shl_ult_const(i64 %x) {
 ; CHECK-LABEL: @scalar_i64_shl_ult_const(
-; CHECK-NEXT:    [[SHL:%.*]] = shl i64 [[X:%.*]], 25
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i64 [[SHL]], 8589934592
+; CHECK-NEXT:    [[TMP1:%.*]] = and i64 [[X:%.*]], 549755813632
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i64 [[TMP1]], 0
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %shl = shl i64 %x, 25
@@ -79,8 +79,8 @@ define i1 @scalar_i64_shl_ult_const(i64 %x) {
 ; Check 'uge' predicate
 define i1 @scalar_i8_shl_uge_const(i8 %x) {
 ; CHECK-LABEL: @scalar_i8_shl_uge_const(
-; CHECK-NEXT:    [[SHL:%.*]] = shl i8 [[X:%.*]], 5
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i8 [[SHL]], 63
+; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[X:%.*]], 6
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8 [[TMP1]], 0
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %shl = shl i8 %x, 5
@@ -91,8 +91,8 @@ define i1 @scalar_i8_shl_uge_const(i8 %x) {
 ; Check 'ule' predicate
 define i1 @scalar_i8_shl_ule_const(i8 %x) {
 ; CHECK-LABEL: @scalar_i8_shl_ule_const(
-; CHECK-NEXT:    [[SHL:%.*]] = shl i8 [[X:%.*]], 5
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i8 [[SHL]], 64
+; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[X:%.*]], 6
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[TMP1]], 0
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %shl = shl i8 %x, 5
@@ -103,8 +103,8 @@ define i1 @scalar_i8_shl_ule_const(i8 %x) {
 ; Check 'ugt' predicate
 define i1 @scalar_i8_shl_ugt_const(i8 %x) {
 ; CHECK-LABEL: @scalar_i8_shl_ugt_const(
-; CHECK-NEXT:    [[SHL:%.*]] = shl i8 [[X:%.*]], 5
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i8 [[SHL]], 63
+; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[X:%.*]], 6
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8 [[TMP1]], 0
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %shl = shl i8 %x, 5
@@ -116,8 +116,8 @@ define i1 @scalar_i8_shl_ugt_const(i8 %x) {
 
 define <4 x i1> @vector_4xi32_shl_ult_const(<4 x i32> %x) {
 ; CHECK-LABEL: @vector_4xi32_shl_ult_const(
-; CHECK-NEXT:    [[SHL:%.*]] = shl <4 x i32> [[X:%.*]], <i32 11, i32 11, i32 11, i32 11>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult <4 x i32> [[SHL]], <i32 131072, i32 131072, i32 131072, i32 131072>
+; CHECK-NEXT:    [[TMP1:%.*]] = and <4 x i32> [[X:%.*]], <i32 2097088, i32 2097088, i32 2097088, i32 2097088>
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq <4 x i32> [[TMP1]], zeroinitializer
 ; CHECK-NEXT:    ret <4 x i1> [[CMP]]
 ;
   %shl = shl <4 x i32> %x, <i32 11, i32 11, i32 11, i32 11>
@@ -161,8 +161,8 @@ define <4 x i1> @vector_4xi32_shl_ult_const_undef3(<4 x i32> %x) {
 ; Check 'uge' predicate
 define <4 x i1> @vector_4xi32_shl_uge_const(<4 x i32> %x) {
 ; CHECK-LABEL: @vector_4xi32_shl_uge_const(
-; CHECK-NEXT:    [[SHL:%.*]] = shl <4 x i32> [[X:%.*]], <i32 11, i32 11, i32 11, i32 11>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt <4 x i32> [[SHL]], <i32 131071, i32 131071, i32 131071, i32 131071>
+; CHECK-NEXT:    [[TMP1:%.*]] = and <4 x i32> [[X:%.*]], <i32 2097088, i32 2097088, i32 2097088, i32 2097088>
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne <4 x i32> [[TMP1]], zeroinitializer
 ; CHECK-NEXT:    ret <4 x i1> [[CMP]]
 ;
   %shl = shl <4 x i32> %x, <i32 11, i32 11, i32 11, i32 11>
@@ -173,8 +173,8 @@ define <4 x i1> @vector_4xi32_shl_uge_const(<4 x i32> %x) {
 ; Check 'ule' predicate
 define <4 x i1> @vector_4xi32_shl_ule_const(<4 x i32> %x) {
 ; CHECK-LABEL: @vector_4xi32_shl_ule_const(
-; CHECK-NEXT:    [[SHL:%.*]] = shl <4 x i32> [[X:%.*]], <i32 11, i32 11, i32 11, i32 11>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult <4 x i32> [[SHL]], <i32 131072, i32 131072, i32 131072, i32 131072>
+; CHECK-NEXT:    [[TMP1:%.*]] = and <4 x i32> [[X:%.*]], <i32 2097088, i32 2097088, i32 2097088, i32 2097088>
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq <4 x i32> [[TMP1]], zeroinitializer
 ; CHECK-NEXT:    ret <4 x i1> [[CMP]]
 ;
   %shl = shl <4 x i32> %x, <i32 11, i32 11, i32 11, i32 11>
@@ -185,8 +185,8 @@ define <4 x i1> @vector_4xi32_shl_ule_const(<4 x i32> %x) {
 ; Check 'ugt' predicate
 define <4 x i1> @vector_4xi32_shl_ugt_const(<4 x i32> %x) {
 ; CHECK-LABEL: @vector_4xi32_shl_ugt_const(
-; CHECK-NEXT:    [[SHL:%.*]] = shl <4 x i32> [[X:%.*]], <i32 11, i32 11, i32 11, i32 11>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt <4 x i32> [[SHL]], <i32 131071, i32 131071, i32 131071, i32 131071>
+; CHECK-NEXT:    [[TMP1:%.*]] = and <4 x i32> [[X:%.*]], <i32 2097088, i32 2097088, i32 2097088, i32 2097088>
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne <4 x i32> [[TMP1]], zeroinitializer
 ; CHECK-NEXT:    ret <4 x i1> [[CMP]]
 ;
   %shl = shl <4 x i32> %x, <i32 11, i32 11, i32 11, i32 11>