[llvm] 748ecc6 - [ValueTracking] add range limits for ctpop

[Sanjay Patel via llvm-commits]

Author: Sanjay Patel
Date: 2020-10-23T08:17:54-04:00
New Revision: 748ecc6b326082c72f5d0866fd7cae499516c079

URL: https://github.com/llvm/llvm-project/commit/748ecc6b326082c72f5d0866fd7cae499516c079
DIFF: https://github.com/llvm/llvm-project/commit/748ecc6b326082c72f5d0866fd7cae499516c079.diff

LOG: [ValueTracking] add range limits for ctpop

As discussed in D89952,
instcombine can sometimes find a way to reduce similar patterns,
but it is incomplete.
InstSimplify uses the computeConstantRange() ValueTracking analysis
via simplifyICmpWithConstant(), so we just need to fill in the max
value of ctpop to process any "icmp pred ctpop(X), C" pattern (the
min value is initialized to zero automatically).

Differential Revision: https://reviews.llvm.org/D89976

Added: 
    

Modified: 
    llvm/lib/Analysis/ValueTracking.cpp
    llvm/test/Transforms/InstSimplify/compare.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 9ecc5ce85e65..7124ca8cc7af 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -6460,6 +6460,11 @@ static void setLimitsForIntrinsic(const IntrinsicInst &II, APInt &Lower,
   unsigned Width = Lower.getBitWidth();
   const APInt *C;
   switch (II.getIntrinsicID()) {
+  case Intrinsic::ctpop:
+    // Maximum of set bits is the bit width.
+    assert(Lower == 0 && "Expected lower bound to be zero");
+    Upper = Width + 1;
+    break;
   case Intrinsic::uadd_sat:
     // uadd.sat(x, C) produces [C, UINT_MAX].
     if (match(II.getOperand(0), m_APInt(C)) ||

diff  --git a/llvm/test/Transforms/InstSimplify/compare.ll b/llvm/test/Transforms/InstSimplify/compare.ll
index 5779f78573e6..592e8c6d7cbc 100644
--- a/llvm/test/Transforms/InstSimplify/compare.ll
+++ b/llvm/test/Transforms/InstSimplify/compare.ll
@@ -2073,9 +2073,7 @@ declare <2 x i13> @llvm.ctpop.v2i13(<2 x i13>)
 
 define i1 @ctpop_sgt_bitwidth(i11 %x) {
 ; CHECK-LABEL: @ctpop_sgt_bitwidth(
-; CHECK-NEXT:    [[POP:%.*]] = call i11 @llvm.ctpop.i11(i11 [[X:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i11 [[POP]], 11
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %pop = call i11 @llvm.ctpop.i11(i11 %x)
   %cmp = icmp sgt i11 %pop, 11
@@ -2084,9 +2082,7 @@ define i1 @ctpop_sgt_bitwidth(i11 %x) {
 
 define i1 @ctpop_sle_minus1(i11 %x) {
 ; CHECK-LABEL: @ctpop_sle_minus1(
-; CHECK-NEXT:    [[POP:%.*]] = call i11 @llvm.ctpop.i11(i11 [[X:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sle i11 [[POP]], -1
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %pop = call i11 @llvm.ctpop.i11(i11 %x)
   %cmp = icmp sle i11 %pop, -1
@@ -2095,15 +2091,15 @@ define i1 @ctpop_sle_minus1(i11 %x) {
 
 define i1 @ctpop_ugt_bitwidth(i73 %x) {
 ; CHECK-LABEL: @ctpop_ugt_bitwidth(
-; CHECK-NEXT:    [[POP:%.*]] = call i73 @llvm.ctpop.i73(i73 [[X:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i73 [[POP]], 73
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %pop = call i73 @llvm.ctpop.i73(i73 %x)
   %cmp = icmp ugt i73 %pop, 73
   ret i1 %cmp
 }
 
+; Negative test - does not simplify, but instcombine could reduce this.
+
 define i1 @ctpop_ugt_bitwidth_minus1(i73 %x) {
 ; CHECK-LABEL: @ctpop_ugt_bitwidth_minus1(
 ; CHECK-NEXT:    [[POP:%.*]] = call i73 @llvm.ctpop.i73(i73 [[X:%.*]])
@@ -2117,9 +2113,7 @@ define i1 @ctpop_ugt_bitwidth_minus1(i73 %x) {
 
 define <2 x i1> @ctpop_sgt_bitwidth_splat(<2 x i13> %x) {
 ; CHECK-LABEL: @ctpop_sgt_bitwidth_splat(
-; CHECK-NEXT:    [[POP:%.*]] = call <2 x i13> @llvm.ctpop.v2i13(<2 x i13> [[X:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt <2 x i13> [[POP]], <i13 13, i13 13>
-; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+; CHECK-NEXT:    ret <2 x i1> zeroinitializer
 ;
   %pop = call <2 x i13> @llvm.ctpop.v2i13(<2 x i13> %x)
   %cmp = icmp sgt <2 x i13> %pop, <i13 13, i13 13>
@@ -2128,9 +2122,7 @@ define <2 x i1> @ctpop_sgt_bitwidth_splat(<2 x i13> %x) {
 
 define i1 @ctpop_ult_plus1_bitwidth(i11 %x) {
 ; CHECK-LABEL: @ctpop_ult_plus1_bitwidth(
-; CHECK-NEXT:    [[POP:%.*]] = call i11 @llvm.ctpop.i11(i11 [[X:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i11 [[POP]], 12
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %pop = call i11 @llvm.ctpop.i11(i11 %x)
   %cmp = icmp ult i11 %pop, 12
@@ -2139,9 +2131,7 @@ define i1 @ctpop_ult_plus1_bitwidth(i11 %x) {
 
 define i1 @ctpop_ne_big_bitwidth(i73 %x) {
 ; CHECK-LABEL: @ctpop_ne_big_bitwidth(
-; CHECK-NEXT:    [[POP:%.*]] = call i73 @llvm.ctpop.i73(i73 [[X:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i73 [[POP]], 75
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %pop = call i73 @llvm.ctpop.i73(i73 %x)
   %cmp = icmp ne i73 %pop, 75
@@ -2150,15 +2140,15 @@ define i1 @ctpop_ne_big_bitwidth(i73 %x) {
 
 define <2 x i1> @ctpop_slt_bitwidth_plus1_splat(<2 x i13> %x) {
 ; CHECK-LABEL: @ctpop_slt_bitwidth_plus1_splat(
-; CHECK-NEXT:    [[POP:%.*]] = call <2 x i13> @llvm.ctpop.v2i13(<2 x i13> [[X:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt <2 x i13> [[POP]], <i13 14, i13 14>
-; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+; CHECK-NEXT:    ret <2 x i1> <i1 true, i1 true>
 ;
   %pop = call <2 x i13> @llvm.ctpop.v2i13(<2 x i13> %x)
   %cmp = icmp slt <2 x i13> %pop, <i13 14, i13 14>
   ret <2 x i1> %cmp
 }
 
+; Negative test - does not simplify, but instcombine could reduce this.
+
 define <2 x i1> @ctpop_slt_bitwidth_splat(<2 x i13> %x) {
 ; CHECK-LABEL: @ctpop_slt_bitwidth_splat(
 ; CHECK-NEXT:    [[POP:%.*]] = call <2 x i13> @llvm.ctpop.v2i13(<2 x i13> [[X:%.*]])