[InstCombine] Add range metadata to cttz/ctlz/ctpop intrinsic calls based on known...

Summary:
I noticed that passing known bits across these intrinsics isn't great at capturing the information we really know. Turning known bits of the input into known bits of a count output isn't able to convey a lot of what we really know.

This patch adds range metadata to these intrinsics based on the known bits.

Currently the patch punts if we already have range metadata present.

Reviewers: spatel, RKSimon, davide, majnemer

Reviewed By: RKSimon

Subscribers: sanjoy, hfinkel, llvm-commits

Differential Revision: https://reviews.llvm.org/D32582

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305927 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineCalls.cpp b/lib/Transforms/InstCombine/InstCombineCalls.cpp
index c0830a5..dbed7ad 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1409,6 +1409,47 @@ static Instruction *foldCttzCtlz(IntrinsicInst &II, InstCombiner &IC) {
     }
   }
 
+  // Add range metadata since known bits can't completely reflect what we know.
+  // TODO: Handle splat vectors.
+  auto *IT = dyn_cast<IntegerType>(Op0->getType());
+  if (IT && IT->getBitWidth() != 1 && !II.getMetadata(LLVMContext::MD_range)) {
+    Metadata *LowAndHigh[] = {
+        ConstantAsMetadata::get(ConstantInt::get(IT, DefiniteZeros)),
+        ConstantAsMetadata::get(ConstantInt::get(IT, PossibleZeros + 1))};
+    II.setMetadata(LLVMContext::MD_range,
+                   MDNode::get(II.getContext(), LowAndHigh));
+    return &II;
+  }
+
+  return nullptr;
+}
+
+static Instruction *foldCtpop(IntrinsicInst &II, InstCombiner &IC) {
+  assert(II.getIntrinsicID() == Intrinsic::ctpop &&
+         "Expected ctpop intrinsic");
+  Value *Op0 = II.getArgOperand(0);
+  // FIXME: Try to simplify vectors of integers.
+  auto *IT = dyn_cast<IntegerType>(Op0->getType());
+  if (!IT)
+    return nullptr;
+
+  unsigned BitWidth = IT->getBitWidth();
+  KnownBits Known(BitWidth);
+  IC.computeKnownBits(Op0, Known, 0, &II);
+
+  unsigned MinCount = Known.countMinPopulation();
+  unsigned MaxCount = Known.countMaxPopulation();
+
+  // Add range metadata since known bits can't completely reflect what we know.
+  if (IT->getBitWidth() != 1 && !II.getMetadata(LLVMContext::MD_range)) {
+    Metadata *LowAndHigh[] = {
+        ConstantAsMetadata::get(ConstantInt::get(IT, MinCount)),
+        ConstantAsMetadata::get(ConstantInt::get(IT, MaxCount + 1))};
+    II.setMetadata(LLVMContext::MD_range,
+                   MDNode::get(II.getContext(), LowAndHigh));
+    return &II;
+  }
+
   return nullptr;
 }
 
@@ -1981,6 +2022,11 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
       return I;
     break;
 
+  case Intrinsic::ctpop:
+    if (auto *I = foldCtpop(*II, *this))
+      return I;
+    break;
+
   case Intrinsic::uadd_with_overflow:
   case Intrinsic::sadd_with_overflow:
   case Intrinsic::umul_with_overflow:

diff --git a/test/Transforms/InstCombine/ctpop.ll b/test/Transforms/InstCombine/ctpop.ll
index d49a907..e8e3603 100644 (file)
--- a/test/Transforms/InstCombine/ctpop.ll
+++ b/test/Transforms/InstCombine/ctpop.ll
@@ -3,6 +3,8 @@
 
 declare i32 @llvm.ctpop.i32(i32)
 declare i8 @llvm.ctpop.i8(i8)
+declare i1 @llvm.ctpop.i1(i1)
+declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32>)
 declare void @llvm.assume(i1)
 
 define i1 @test1(i32 %arg) {
@@ -44,7 +46,7 @@ define i1 @test3(i32 %arg) {
 ; Negative test for when we know nothing
 define i1 @test4(i8 %arg) {
 ; CHECK-LABEL: @test4(
-; CHECK-NEXT:    [[CNT:%.*]] = call i8 @llvm.ctpop.i8(i8 [[ARG:%.*]])
+; CHECK-NEXT:    [[CNT:%.*]] = call i8 @llvm.ctpop.i8(i8 [[ARG:%.*]]), !range ![[RANGE:[0-9]+]]
 ; CHECK-NEXT:    [[RES:%.*]] = icmp eq i8 [[CNT]], 2
 ; CHECK-NEXT:    ret i1 [[RES]]
 ;
@@ -55,16 +57,41 @@ define i1 @test4(i8 %arg) {
 
 ; Test when the number of possible known bits isn't one less than a power of 2
 ; and the compare value is greater but less than the next power of 2.
-; TODO: The icmp is unnecessary given the known bits of the input.
 define i1 @test5(i32 %arg) {
 ; CHECK-LABEL: @test5(
-; CHECK-NEXT:    [[AND:%.*]] = and i32 [[ARG:%.*]], 3
-; CHECK-NEXT:    [[CNT:%.*]] = call i32 @llvm.ctpop.i32(i32 [[AND]])
-; CHECK-NEXT:    [[RES:%.*]] = icmp eq i32 [[CNT]], 3
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 false
 ;
   %and = and i32 %arg, 3
   %cnt = call i32 @llvm.ctpop.i32(i32 %and)
   %res = icmp eq i32 %cnt, 3
   ret i1 %res
 }
+
+; Test when the number of possible known bits isn't one less than a power of 2
+; and the compare value is greater but less than the next power of 2.
+; TODO: The icmp is unnecessary given the known bits of the input, but range
+; metadata doesn't support vectors
+define <2 x i1> @test5vec(<2 x i32> %arg) {
+; CHECK-LABEL: @test5vec(
+; CHECK-NEXT:    [[AND:%.*]] = and <2 x i32> [[ARG:%.*]], <i32 3, i32 3>
+; CHECK-NEXT:    [[CNT:%.*]] = call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> [[AND]])
+; CHECK-NEXT:    [[RES:%.*]] = icmp eq <2 x i32> [[CNT]], <i32 3, i32 3>
+; CHECK-NEXT:    ret <2 x i1> [[RES]]
+;
+  %and = and <2 x i32> %arg, <i32 3, i32 3>
+  %cnt = call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> %and)
+  %res = icmp eq <2 x i32> %cnt, <i32 3, i32 3>
+  ret <2 x i1> %res
+}
+
+; Make sure we don't add range metadata to i1 ctpop.
+define i1 @test6(i1 %arg) {
+; CHECK-LABEL: @test6(
+; CHECK-NEXT:    [[CNT:%.*]] = call i1 @llvm.ctpop.i1(i1 [[ARG:%.*]])
+; CHECK-NEXT:    ret i1 [[CNT]]
+;
+  %cnt = call i1 @llvm.ctpop.i1(i1 %arg)
+  ret i1 %cnt
+}
+
+; CHECK: ![[RANGE]] = !{i8 0, i8 9}

diff --git a/test/Transforms/InstCombine/intrinsics.ll b/test/Transforms/InstCombine/intrinsics.ll
index 1b1ed60..c294d79 100644 (file)
--- a/test/Transforms/InstCombine/intrinsics.ll
+++ b/test/Transforms/InstCombine/intrinsics.ll
@@ -16,6 +16,8 @@ declare %ov.result.32 @llvm.umul.with.overflow.i32(i32, i32) nounwind readnone
 declare double @llvm.powi.f64(double, i32) nounwind readonly
 declare i32 @llvm.cttz.i32(i32, i1) nounwind readnone
 declare i32 @llvm.ctlz.i32(i32, i1) nounwind readnone
+declare i1 @llvm.cttz.i1(i1, i1) nounwind readnone
+declare i1 @llvm.ctlz.i1(i1, i1) nounwind readnone
 declare i32 @llvm.ctpop.i32(i32) nounwind readnone
 declare <2 x i32> @llvm.cttz.v2i32(<2 x i32>, i1) nounwind readnone
 declare <2 x i32> @llvm.ctlz.v2i32(<2 x i32>, i1) nounwind readnone
@@ -293,6 +295,16 @@ define <2 x i32> @cttz_vec(<2 x i32> %a) {
   ret <2 x i32> %count
 }
 
+; Make sure we don't add range metadata to i1 cttz.
+define i1 @cttz_i1(i1 %arg) {
+; CHECK-LABEL: @cttz_i1(
+; CHECK-NEXT:    [[CNT:%.*]] = call i1 @llvm.cttz.i1(i1 [[ARG:%.*]], i1 false) #2
+; CHECK-NEXT:    ret i1 [[CNT]]
+;
+  %cnt = call i1 @llvm.cttz.i1(i1 %arg, i1 false) nounwind readnone
+  ret i1 %cnt
+}
+
 define i1 @cttz_knownbits(i32 %arg) {
 ; CHECK-LABEL: @cttz_knownbits(
 ; CHECK-NEXT:    ret i1 false
@@ -316,7 +328,7 @@ define <2 x i1> @cttz_knownbits_vec(<2 x i32> %arg) {
 define i1 @cttz_knownbits2(i32 %arg) {
 ; CHECK-LABEL: @cttz_knownbits2(
 ; CHECK-NEXT:    [[OR:%.*]] = or i32 [[ARG:%.*]], 4
-; CHECK-NEXT:    [[CNT:%.*]] = call i32 @llvm.cttz.i32(i32 [[OR]], i1 true)
+; CHECK-NEXT:    [[CNT:%.*]] = call i32 @llvm.cttz.i32(i32 [[OR]], i1 true) #2, !range ![[CTTZ_RANGE:[0-9]+]]
 ; CHECK-NEXT:    [[RES:%.*]] = icmp eq i32 [[CNT]], 2
 ; CHECK-NEXT:    ret i1 [[RES]]
 ;
@@ -339,13 +351,9 @@ define <2 x i1> @cttz_knownbits2_vec(<2 x i32> %arg) {
   ret <2 x i1> %res
 }
 
-; TODO: The icmp is unnecessary given the known bits of the input.
 define i1 @cttz_knownbits3(i32 %arg) {
 ; CHECK-LABEL: @cttz_knownbits3(
-; CHECK-NEXT:    [[OR:%.*]] = or i32 [[ARG:%.*]], 4
-; CHECK-NEXT:    [[CNT:%.*]] = call i32 @llvm.cttz.i32(i32 [[OR]], i1 true) #2
-; CHECK-NEXT:    [[RES:%.*]] = icmp eq i32 [[CNT]], 3
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 false
 ;
   %or = or i32 %arg, 4
   %cnt = call i32 @llvm.cttz.i32(i32 %or, i1 true) nounwind readnone
@@ -387,6 +395,16 @@ define <2 x i8> @ctlz_vec(<2 x i8> %a) {
   ret <2 x i8> %count
 }
 
+; Make sure we don't add range metadata to i1 ctlz.
+define i1 @ctlz_i1(i1 %arg) {
+; CHECK-LABEL: @ctlz_i1(
+; CHECK-NEXT:    [[CNT:%.*]] = call i1 @llvm.ctlz.i1(i1 [[ARG:%.*]], i1 false) #2
+; CHECK-NEXT:    ret i1 [[CNT]]
+;
+  %cnt = call i1 @llvm.ctlz.i1(i1 %arg, i1 false) nounwind readnone
+  ret i1 %cnt
+}
+
 define i1 @ctlz_knownbits(i8 %arg) {
 ; CHECK-LABEL: @ctlz_knownbits(
 ; CHECK-NEXT:    ret i1 false
@@ -410,7 +428,7 @@ define <2 x i1> @ctlz_knownbits_vec(<2 x i8> %arg) {
 define i1 @ctlz_knownbits2(i8 %arg) {
 ; CHECK-LABEL: @ctlz_knownbits2(
 ; CHECK-NEXT:    [[OR:%.*]] = or i8 [[ARG:%.*]], 32
-; CHECK-NEXT:    [[CNT:%.*]] = call i8 @llvm.ctlz.i8(i8 [[OR]], i1 true)
+; CHECK-NEXT:    [[CNT:%.*]] = call i8 @llvm.ctlz.i8(i8 [[OR]], i1 true) #2, !range ![[CTLZ_RANGE:[0-9]+]]
 ; CHECK-NEXT:    [[RES:%.*]] = icmp eq i8 [[CNT]], 2
 ; CHECK-NEXT:    ret i1 [[RES]]
 ;
@@ -433,13 +451,9 @@ define <2 x i1> @ctlz_knownbits2_vec(<2 x i8> %arg) {
   ret <2 x i1> %res
 }
 
-; TODO: The icmp is unnecessary given the known bits of the input.
 define i1 @ctlz_knownbits3(i8 %arg) {
 ; CHECK-LABEL: @ctlz_knownbits3(
-; CHECK-NEXT:    [[OR:%.*]] = or i8 [[ARG:%.*]], 32
-; CHECK-NEXT:    [[CNT:%.*]] = call i8 @llvm.ctlz.i8(i8 [[OR]], i1 true) #2
-; CHECK-NEXT:    [[RES:%.*]] = icmp eq i8 [[CNT]], 3
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 false
 ;
   %or = or i8 %arg, 32
   %cnt = call i8 @llvm.ctlz.i8(i8 %or, i1 true) nounwind readnone
@@ -790,3 +804,6 @@ define void @nearbyint(double *%P) {
   store volatile double %C, double* %P
   ret void
 }
+
+; CHECK: [[CTTZ_RANGE]] = !{i32 0, i32 3}
+; CHECK: [[CTLZ_RANGE]] = !{i8 0, i8 3}