[llvm] 3fb0d6b - [ValueTracking] add range limits for ctlz

[Sanjay Patel via llvm-commits]

Author: Sanjay Patel
Date: 2020-10-23T08:43:45-04:00
New Revision: 3fb0d6b0d55b52a214a3e5118dda3c7d3422782a

URL: https://github.com/llvm/llvm-project/commit/3fb0d6b0d55b52a214a3e5118dda3c7d3422782a
DIFF: https://github.com/llvm/llvm-project/commit/3fb0d6b0d55b52a214a3e5118dda3c7d3422782a.diff

LOG: [ValueTracking] add range limits for ctlz

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 ctlz to process any "icmp pred ctlz(X), C" pattern (the
min value is initialized to zero automatically).

Follow-up to 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 7124ca8cc7af..e277b02720ea 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -6461,7 +6461,8 @@ static void setLimitsForIntrinsic(const IntrinsicInst &II, APInt &Lower,
   const APInt *C;
   switch (II.getIntrinsicID()) {
   case Intrinsic::ctpop:
-    // Maximum of set bits is the bit width.
+  case Intrinsic::ctlz:
+    // Maximum of set/clear bits is the bit width.
     assert(Lower == 0 && "Expected lower bound to be zero");
     Upper = Width + 1;
     break;

diff  --git a/llvm/test/Transforms/InstSimplify/compare.ll b/llvm/test/Transforms/InstSimplify/compare.ll
index 4e6e286d5c62..d024d7096272 100644
--- a/llvm/test/Transforms/InstSimplify/compare.ll
+++ b/llvm/test/Transforms/InstSimplify/compare.ll
@@ -2166,9 +2166,7 @@ declare <2 x i13> @llvm.ctlz.v2i13(<2 x i13>)
 
 define i1 @ctlz_sgt_bitwidth(i11 %x) {
 ; CHECK-LABEL: @ctlz_sgt_bitwidth(
-; CHECK-NEXT:    [[POP:%.*]] = call i11 @llvm.ctlz.i11(i11 [[X:%.*]], i1 false)
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i11 [[POP]], 11
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %pop = call i11 @llvm.ctlz.i11(i11 %x)
   %cmp = icmp sgt i11 %pop, 11
@@ -2177,9 +2175,7 @@ define i1 @ctlz_sgt_bitwidth(i11 %x) {
 
 define i1 @ctlz_sle_minus1(i11 %x) {
 ; CHECK-LABEL: @ctlz_sle_minus1(
-; CHECK-NEXT:    [[POP:%.*]] = call i11 @llvm.ctlz.i11(i11 [[X:%.*]], i1 false)
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sle i11 [[POP]], -1
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %pop = call i11 @llvm.ctlz.i11(i11 %x)
   %cmp = icmp sle i11 %pop, -1
@@ -2188,9 +2184,7 @@ define i1 @ctlz_sle_minus1(i11 %x) {
 
 define i1 @ctlz_ugt_bitwidth(i73 %x) {
 ; CHECK-LABEL: @ctlz_ugt_bitwidth(
-; CHECK-NEXT:    [[POP:%.*]] = call i73 @llvm.ctlz.i73(i73 [[X:%.*]], i1 false)
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i73 [[POP]], 73
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %pop = call i73 @llvm.ctlz.i73(i73 %x)
   %cmp = icmp ugt i73 %pop, 73
@@ -2212,9 +2206,7 @@ define i1 @ctlz_ugt_bitwidth_minus1(i73 %x) {
 
 define <2 x i1> @ctlz_sgt_bitwidth_splat(<2 x i13> %x) {
 ; CHECK-LABEL: @ctlz_sgt_bitwidth_splat(
-; CHECK-NEXT:    [[POP:%.*]] = call <2 x i13> @llvm.ctlz.v2i13(<2 x i13> [[X:%.*]], i1 false)
-; 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.ctlz.v2i13(<2 x i13> %x)
   %cmp = icmp sgt <2 x i13> %pop, <i13 13, i13 13>
@@ -2223,9 +2215,7 @@ define <2 x i1> @ctlz_sgt_bitwidth_splat(<2 x i13> %x) {
 
 define i1 @ctlz_ult_plus1_bitwidth(i11 %x) {
 ; CHECK-LABEL: @ctlz_ult_plus1_bitwidth(
-; CHECK-NEXT:    [[POP:%.*]] = call i11 @llvm.ctlz.i11(i11 [[X:%.*]], i1 false)
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i11 [[POP]], 12
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %pop = call i11 @llvm.ctlz.i11(i11 %x)
   %cmp = icmp ult i11 %pop, 12
@@ -2234,9 +2224,7 @@ define i1 @ctlz_ult_plus1_bitwidth(i11 %x) {
 
 define i1 @ctlz_ne_big_bitwidth(i73 %x) {
 ; CHECK-LABEL: @ctlz_ne_big_bitwidth(
-; CHECK-NEXT:    [[POP:%.*]] = call i73 @llvm.ctlz.i73(i73 [[X:%.*]], i1 false)
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i73 [[POP]], 75
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %pop = call i73 @llvm.ctlz.i73(i73 %x)
   %cmp = icmp ne i73 %pop, 75
@@ -2245,9 +2233,7 @@ define i1 @ctlz_ne_big_bitwidth(i73 %x) {
 
 define <2 x i1> @ctlz_slt_bitwidth_plus1_splat(<2 x i13> %x) {
 ; CHECK-LABEL: @ctlz_slt_bitwidth_plus1_splat(
-; CHECK-NEXT:    [[POP:%.*]] = call <2 x i13> @llvm.ctlz.v2i13(<2 x i13> [[X:%.*]], i1 false)
-; 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.ctlz.v2i13(<2 x i13> %x)
   %cmp = icmp slt <2 x i13> %pop, <i13 14, i13 14>